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Pneumonia is an
inflammatory Inflammatory may refer to: * Inflammation, a biological response to harmful stimuli * The word ''inflammatory'' is also used to refer literally to fire and flammability, and figuratively in relation to comments that are Agent provocateur, provocati ...
condition of the
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
primarily affecting the small air sacs known as
alveoli Alveolus (pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Alveolus may refer to: In anatomy and zoology in general * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ...
. Symptoms typically include some combination of
productive Productivity describes various measures of the efficiency Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, i ...
or dry
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an o ...
,
chest pain Chest pain is pain or discomfort in the chest, typically the front of the chest. It may be described as sharp, dull, pressure, heaviness or squeezing. Associated symptoms may include pain in the shoulder, arm, upper abdomen, or jaw, along with na ...
,
fever Fever, also referred to as pyrexia, is defined as having a above the due to an increase in the body's temperature . There is not a single agreed-upon upper limit for normal temperature with sources using values between in humans. The increa ...

fever
, and difficulty breathing. The severity of the condition is variable. Pneumonia is usually caused by
infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of tissues to the infectious agents and the s they produce. An infectious disease, also known as a transmissible disease or communicable disease, i ...

infection
with
virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecu ...

virus
es or
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sm ...

bacteria
, and less commonly by other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
s. Identifying the responsible pathogen can be difficult. Diagnosis is often based on symptoms and
physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient A patient is any recipient of health care Health care, health-care, or healthcare is the maintenance or improvement of health ...

physical examination
.
Chest X-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a Projectional radiography, projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most ...
s, blood tests, and
culture Culture () is an umbrella term which encompasses the social behavior and Norm (social), norms found in human Society, societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, and habits of the individuals i ...
of the
sputum Sputum is mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous an ...
may help confirm the diagnosis. The disease may be classified by where it was acquired, such as community- or hospital-acquired or healthcare-associated pneumonia. Risk factors for pneumonia include
cystic fibrosis Cystic fibrosis (CF) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Johan ...
,
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
(COPD),
sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in ...
,
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
,
diabetes Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorders characterized by a hyperglycemia, high blood sugar level over a prolonged period of time. Symptoms often include frequent urination, Polydipsia, increased th ...

diabetes
,
heart failure Heart failure (HF), also known as congestive heart failure (CHF) and (congestive) cardiac failure (CCF), is a Syndrome, set of manifestations caused by the failure of the heart's function as a pump supporting the Circulatory system, blood flow t ...
, a history of
smoking Smoking is a practice in which a substance is burned and the resulting smoke Smoke is a collection of airborne and es emitted when a material undergoes or , together with the quantity of air that is or otherwise mixed into the ma ...

smoking
, a poor ability to cough (such as following a
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Dis ...

stroke
), and a weak immune system.
Vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed for ...

Vaccine
s to prevent certain types of pneumonia (such as those caused by ''
Streptococcus pneumoniae ''Streptococcus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...

Streptococcus pneumoniae
'' bacteria, linked to
influenza Influenza, commonly known as "the flu", is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), ...

influenza
, or linked to
COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease A contagious disease is a disease A disease is a particular abnormal condition that negatively affects the structure A structure is an arrangement and organization o ...

COVID-19
) are available. Other methods of prevention include
hand washing Hand washing (or handwashing), also known as hand hygiene, is the act of cleaning one's hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the El ...

hand washing
to prevent infection, not smoking, and social distancing. Treatment depends on the underlying cause. Pneumonia believed to be due to bacteria is treated with
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
s. If the pneumonia is severe, the affected person is generally hospitalized.
Oxygen therapy Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

Oxygen therapy
may be used if oxygen levels are low. Each year, pneumonia affects about 450 million people globally (7% of the population) and results in about 4 million deaths. With the introduction of antibiotics and vaccines in the 20th century, survival has greatly improved. Nevertheless, pneumonia remains a
leading cause of death The following is a list of the causes of human deaths worldwide for different years arranged by their associated mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a pa ...
in developing countries, and also among the very old, the very young, and the chronically ill. Pneumonia often shortens the period of suffering among those already close to death and has thus been called "the old man's friend".


Signs and symptoms

People with infectious pneumonia often have a
productive cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an o ...
,
fever Fever, also referred to as pyrexia, is defined as having a above the due to an increase in the body's temperature . There is not a single agreed-upon upper limit for normal temperature with sources using values between in humans. The increa ...

fever
accompanied by shaking chills,
shortness of breath Shortness of breath (SOB), also known as dyspnea (BrE British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificat ...
, sharp or stabbing
chest pain Chest pain is pain or discomfort in the chest, typically the front of the chest. It may be described as sharp, dull, pressure, heaviness or squeezing. Associated symptoms may include pain in the shoulder, arm, upper abdomen, or jaw, along with na ...
during deep breaths, and an increased rate of breathing. In elderly people, confusion may be the most prominent sign. The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing. Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease,
malnutrition Malnutrition is 'a state of nutrition in which a deficiency or excess (or imbalance) of energy, protein and other nutrients causes measurable adverse effect on tissue and body form (body shape, size and composition) and function and clinical ou ...
or in the elderly. In addition, a cough is frequently absent in children less than 2 months old. More severe signs and symptoms in children may include blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness. Bacterial and viral cases of pneumonia usually result in similar symptoms. Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by ''
Legionella ''Legionella'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to ...
'' may occur with abdominal pain,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
, or confusion. Pneumonia caused by ''
Streptococcus pneumoniae ''Streptococcus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...

Streptococcus pneumoniae
'' is associated with rusty colored sputum. Pneumonia caused by ''
Klebsiella ''Klebsiella'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses ...
'' may have bloody sputum often described as "currant jelly". Bloody sputum (known as
hemoptysis Hemoptysis is the coughing up of blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells and transports metabolic waste products away from those s ...

hemoptysis
) may also occur with
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
, Gram-negative pneumonia,
lung abscess Lung abscess is a type of liquefactive necrosisLiquefactive necrosis (or colliquative necrosis) is a type of necrosis which results in a transformation of the tissue into a liquid viscous mass.Robbins and Cotran: Pathologic Basis of Disease, 8th Ed ...
es and more commonly
acute bronchitis Acute bronchitis, also known as a chest cold, is short-term bronchitis Bronchitis is inflammation of the bronchi A bronchus is a passage or airway in the respiratory system The respiratory system (also respiratory apparatus, ventilatory s ...
. Pneumonia caused by ''
Mycoplasma pneumoniae ''Mycoplasma pneumoniae'' is a very small bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typic ...
'' may occur in association with swelling of the lymph nodes in the neck,
joint pain Arthralgia (from Greek ''arthro-'', joint + ''-algos'', pain) literally means ''joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes pa ...
, or a
middle ear infection Otitis media is a group of inflammatory diseases of the middle ear The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. The mammalian middle ear contains three ossicles, which trans ...
. Viral pneumonia presents more commonly with
wheezing A wheeze is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed (for example narrowing of the lower respiratory tract ...
than bacterial pneumonia. Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause. However, evidence has not supported this distinction, therefore it is no longer emphasized.


Cause

Pneumonia is due to infections caused primarily by
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sm ...

bacteria
or
virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecu ...

virus
es and less commonly by
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
and
parasites Parasitism is a symbiotic Symbiosis (from Ancient Greek, Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different Organism, biological or ...
. Although more than 100 strains of infectious agents have been identified, only a few are responsible for the majority of cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults. A causative agent may not be isolated in about half of cases despite careful testing. In an active population-based surveillance for community-acquired pneumonia requiring hospitalization in five hospitals in Chicago and Nashville from January 2010 through June 2012, 2259 patients were identified who had radiographic evidence of pneumonia and specimens that could be tested for the responsible pathogen. Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria. Specifically, 23% had one or more viruses, 11% had one or more bacteria, 3% had both bacterial and viral pathogens, and 1% had a fungal or mycobacterial infection. "The most common pathogens were
human rhinovirus The rhinovirus (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 1 ...
(in 9% of patients), influenza virus (in 6%), and ''Streptococcus pneumoniae'' (in 5%)." The term ''pneumonia'' is sometimes more broadly applied to any condition resulting in
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
of the lungs (caused for example by
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of differe ...

autoimmune disease
s, chemical burns or drug reactions); however, this inflammation is more accurately referred to as
pneumonitis Pneumonitis describes general inflammation of lung tissue. Possible causative agents include radiation therapy of the chest, exposure to medications used during chemo-therapy, the inhalation of debris (e.g., animal dander), aspiration, herbicides o ...

pneumonitis
. Factors that predispose to pneumonia include
smoking Smoking is a practice in which a substance is burned and the resulting smoke Smoke is a collection of airborne and es emitted when a material undergoes or , together with the quantity of air that is or otherwise mixed into the ma ...

smoking
,
immunodeficiency Immunodeficiency, also known as immunocompromisation, is a state in which the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...
,
alcoholism Alcoholism is, broadly, any drinking of alcohol In , alcohol is an that carries at least one (−OH) bound to a atom. The term alcohol originally referred to the primary alcohol (ethyl alcohol), which is and is the main alcoho ...
,
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
,
sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in ...
(SCD),
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
,
chronic kidney disease Chronic kidney disease (CKD) is a type of kidney disease in which there is gradual loss of kidney function over a period of months to years. Initially there are generally no symptoms; later, symptoms may include pedal edema, leg swelling, feeling ...
,
liver disease Liver disease (also called hepatic disease) is a type of damage to or disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any imme ...
, and biological aging. Additional risks in children include not being , exposure to cigarette smoke and other air pollution,
malnutrition Malnutrition is 'a state of nutrition in which a deficiency or excess (or imbalance) of energy, protein and other nutrients causes measurable adverse effect on tissue and body form (body shape, size and composition) and function and clinical ou ...
, and poverty. The use of acid-suppressing medications – such as proton-pump inhibitors or
H2 blockers H2 antagonists, sometimes referred to as H2RAs and also called H2 blockers, are a class of medications A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug File:Aspirine macro shot.jp ...
– is associated with an increased risk of pneumonia. Approximately 10% of people who require
mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilationIntermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses p ...
develop
ventilator-associated pneumonia Ventilator-associated pneumonia (VAP) is a type of lung infection that occurs in people who are on mechanical ventilation breathing machines in hospitals. As such, VAP typically affects critically ill persons that are in an intensive care unit (IC ...
, and people with a gastric feeding tube have an increased risk of developing
aspiration pneumonia Aspiration pneumonia is a type of pneumonia, lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complication ...
. For people with certain variants of the FER gene, the risk of death is reduced in
sepsis Sepsis is a life-threatening condition that arises when the body's response to infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction ...
caused by pneumonia. However, for those with
TLR6 Toll-like receptor 6 is a protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in ...
variants, the risk of getting
Legionnaires' disease Legionnaires' disease is a form of atypical pneumonia Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs kno ...
is increased.


Bacteria

Bacteria are the most common cause of
community-acquired pneumonia Community-acquired pneumonia (CAP) refers to pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of ...
(CAP), with ''
Streptococcus pneumoniae ''Streptococcus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...

Streptococcus pneumoniae
'' isolated in nearly 50% of cases. Other commonly isolated bacteria include ''
Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), b ...

Haemophilus influenzae
'' in 20%, ''
Chlamydophila pneumoniae ''Chlamydia pneumoniae'' is a species of ''Chlamydia (genus), Chlamydia'', an Obligate intracellular parasite, obligate intracellular bacterium that infects humans and is a major cause of pneumonia. It was known as the Taiwan acute respiratory ag ...

Chlamydophila pneumoniae
'' in 13%, and ''
Mycoplasma pneumoniae ''Mycoplasma pneumoniae'' is a very small bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typic ...
'' in 3% of cases; ''
Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive bacteria, Gram-positive coccus, round-shaped bacterium, a member of the Firmicutes, and is a usual member of the microbiota of the body, frequently found in the Respiratory tract, upper respiratory ...
''; ''
Moraxella catarrhalis ''Moraxella'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to ...

Moraxella catarrhalis
''; and ''
Legionella pneumophila ''Legionella pneumophila'' is a thin, aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacteri ...
''. A number of
drug-resistant Drug resistance is the reduction in effectiveness of a medication such as an antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organis ...
versions of the above infections are becoming more common, including drug-resistant ''Streptococcus pneumoniae'' (DRSP) and methicillin-resistant ''Staphylococcus aureus'' (MRSA). The spreading of organisms is facilitated by certain risk factors.
Alcoholism Alcoholism is, broadly, any drinking of alcohol In , alcohol is an that carries at least one (−OH) bound to a atom. The term alcohol originally referred to the primary alcohol (ethyl alcohol), which is and is the main alcoho ...
is associated with ''Streptococcus pneumoniae'',
anaerobic organism An anaerobic organism or anaerobe is any organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a syn ...
s, and ''Mycobacterium tuberculosis''; smoking facilitates the effects of ''Streptococcus pneumoniae'', ''Haemophilus influenzae'', ''Moraxella catarrhalis'', and ''Legionella pneumophila''. Exposure to birds is associated with ''
Chlamydia psittaci ''Chlamydia psittaci'' is a lethal intracellular bacterial species that may cause endemic Endemism is the state of a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of ...
''; farm animals with '' Coxiella burnetti''; aspiration of stomach contents with anaerobic organisms; and
cystic fibrosis Cystic fibrosis (CF) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Johan ...
with ''
Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized ...
'' and ''Staphylococcus aureus''. ''Streptococcus pneumoniae'' is more common in the winter, and it should be suspected in persons aspirating a large number of anaerobic organisms.


Viruses

In adults, viruses account for about one third of pneumonia cases, and in children for about 15% of them. Commonly implicated agents include
rhinovirus The rhinovirus (from the grc, ῥίς, rhis "nose", , romanized: "of the nose", and the la, vīrus) is the most common viral infectious agent in humans and is the predominant cause of the common cold The common cold, also known simply a ...
es,
coronavirus Coronaviruses are a group of related Orthornavirae, RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some ca ...

coronavirus
es,
influenza virus ''Orthomyxoviridae'' (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population ...

influenza virus
,
respiratory syncytial virus Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a common, contagious virus that causes infections of the respiratory tract. It is a Negative-strand RNA virus, negative-sense, ...
(RSV),
adenovirus Adenoviruses (members of the family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to ma ...

adenovirus
, and
parainfluenza Human parainfluenza viruses (HPIVs) are the viruses that cause human parainfluenza. HPIVs are a paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor exclud ...
.
Herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names ''Human alphaherpesvirus 1'' and ''Human alphaherpesvirus 2'', are two members of the Herpesviridae#Human herpesvirus types, human ''Herpesviridae'' family, a ...
rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns. After
organ transplantation Organ transplantation is a medical procedure in which an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co- ...
or in otherwise
immunocompromised Immunodeficiency, also known as immunocompromisation, is a state in which the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...
persons, there are high rates of
cytomegalovirus ''Cytomegalovirus'' (''CMV'') (from ''cyto-'' 'cell' via Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. I ...
pneumonia. Those with viral infections may be secondarily infected with the bacteria ''Streptococcus pneumoniae'', ''Staphylococcus aureus'', or ''Haemophilus influenzae'', particularly when other health problems are present. Different viruses predominate at different times of the year; during
flu season Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemispheres of Earth, hemisphere. Influenza activity can sometimes be ...
, for example, influenza may account for more than half of all viral cases. Outbreaks of other viruses also occur occasionally, including
hantaviruses ''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA virus Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large ...
and coronaviruses.
Severe acute respiratory syndrome coronavirus 2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is the coronavirus Coronaviruses are a group of related that cause diseases in s and s. In humans and birds, they cause s that can range from mild to lethal. Mild illnes ...
(SARS-CoV-2) can also result in pneumonia.


Fungi

Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to
AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of ...
,
immunosuppressive drug Immunosuppressive drugs, also known as immunosuppressive agents, immunosuppressants and antirejection medications, are drugs A drug is any chemical substance A chemical substance is a form of matter In classical physics and genera ...
s, or other medical problems. It is most often caused by ''
Histoplasma capsulatum ''Histoplasma capsulatum'' is a species of dimorphic fungus. Its sexual form is called ''Ajellomyces capsulatus''. It can cause pulmonary and disseminated histoplasmosis Histoplasmosis is a disease caused by the fungus '' Histoplasma capsulat ...

Histoplasma capsulatum
'', '' Blastomyces'', ''
Cryptococcus neoformans ''Cryptococcus neoformans'' is an encapsulated yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species ...

Cryptococcus neoformans
'', ''
Pneumocystis jiroveci ''Pneumocystis jirovecii'' (previously ''P. carinii'') is a yeast-like fungus of the genus ''Pneumocystis''. The causative organism of Pneumocystis pneumonia, ''Pneumocystis'' pneumonia, it is an important human pathogen, particularly among immuno ...
'' (pneumocystis pneumonia, or PCP), and ''Coccidioides immitis''. Histoplasmosis is most common in the Mississippi embayment, Mississippi River basin, and coccidioidomycosis is most common in the Southwestern United States. The number of cases of fungal pneumonia has been increasing in the latter half of the 20th century due to increasing travel and rates of immunosuppression in the population. For people infected with HIV/AIDS, PCP is a common opportunistic infection.


Parasites

A variety of parasites can affect the lungs, including ''Toxoplasma gondii'', ''Strongyloides stercoralis'', ''Ascaris lumbricoides'', and ''Plasmodium malariae''.Murray and Nadel (2010). Chapter 37. These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector. Except for ''Paragonimus westermani'', most parasites do not specifically affect the lungs but involve the lungs secondarily to other sites. Some parasites, in particular those belonging to the ''Ascaris'' and ''Strongyloides'' genera, stimulate a strong eosinophilic reaction, which may result in eosinophilic pneumonia. In other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation. In the developed world, these infections are most common in people returning from travel or in immigrants. Around the world, parasitic pneumonia is most common in the immunodeficient.


Noninfectious

Idiopathic interstitial pneumonia or noninfectious pneumonia is a class of diffuse lung diseases. They include diffuse alveolar damage, organizing pneumonia, nonspecific interstitial pneumonia, lymphocytic interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and usual interstitial pneumonia. Lipoid pneumonia is another rare cause due to lipids entering the lung. These lipids can either be inhaled or spread to the lungs from elsewhere in the body.


Mechanisms

Pneumonia frequently starts as an upper respiratory tract infection that moves into the lower respiratory tract. It is a type of pneumonitis (lung inflammation). The normal flora of the upper airway give protection by competing with pathogens for nutrients. In the lower airways, Cough reflex, reflexes of the glottis, actions of complement proteins and immunoglobulins are important for protection. MicroPulmonary aspiration, aspiration of contaminated secretions can infect the lower airways and cause pneumonia. The progress of pneumonia is determined by the virulence of the organism; the amount of organism required to start an infection; and the body's immune response against the infection.


Bacterial

Most bacteria enter the lungs via small Pulmonary aspiration, aspirations of organisms residing in the throat or nose. Half of normal people have these small aspirations during sleep. While the throat always contains bacteria, virulent, potentially infectious ones reside there only at certain times and under certain conditions. A minority of types of bacteria such as ''Mycobacterium tuberculosis'' and ''
Legionella pneumophila ''Legionella pneumophila'' is a thin, aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacteri ...
'' reach the lungs via contaminated airborne droplets. Bacteria can also spread via the blood. Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the macrophages and neutrophils (defensive white blood cells) attempt to inactivate the bacteria. The neutrophils also release cytokines, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray.


Viral

Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then touch their eyes or nose.Murray and Nadel (2010). Chapter 31. Other viral infections occur when contaminated airborne droplets are inhaled through the nose or mouth. Once in the upper airway, the viruses may make their way into the lungs, where they invade the cells lining the airways, alveoli, or lung parenchyma. Some viruses such as measles and herpes simplex may reach the lungs via the blood. The invasion of the lungs may lead to varying degrees of cell death. When the immune system responds to the infection, even more lung damage may occur. Primarily white blood cells, mainly mononuclear cells, generate the inflammation. As well as damaging the lungs, many viruses simultaneously affect other organ (anatomy), organs and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.


Diagnosis

Pneumonia is typically diagnosed based on a combination of physical signs and often a chest X-ray. In adults with normal vital signs and a normal lung examination, the diagnosis is unlikely. However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial cause. The overall impression of a physician appears to be at least as good as decision rules for making or excluding the diagnosis.


Diagnosis in children

The World Health Organization has defined pneumonia in children clinically based on either a
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an o ...
or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness. A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old. In children, low oxygen levels and lower chest indrawing are more Sensitivity and specificity, sensitive than hearing chest crackles with a stethoscope or increased respiratory rate. Grunting and nasal flaring may be other useful signs in children less than five years old. Lack of wheezing is an indicator of ''
Mycoplasma pneumoniae ''Mycoplasma pneumoniae'' is a very small bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typic ...
'' in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not macrolide treatment should be used. The presence of chest pain in children with pneumonia doubles the probability of ''Mycoplasma pneumoniae''.


Diagnosis in adults

In general, in adults, investigations are not needed in mild cases. There is a very low risk of pneumonia if all vital signs and chest auscultation, auscultation are normal. C-reactive protein (CRP) may help support the diagnosis. For those with CRP less than 20 mg/L without convincing evidence of pneumonia, antibiotics are not recommended. Procalcitonin may help determine the cause and support decisions about who should receive antibiotics. Antibiotics are encouraged if the procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L. In people requiring hospitalization, pulse oximetry, chest radiography and blood tests – including a complete blood count, serum electrolytes, C-reactive protein level, and possibly liver function tests – are recommended. The diagnosis of influenza-like illness can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing. Thus, treatment is frequently based on the presence of influenza in the community or a Rapid influenza diagnostic test, rapid influenza test.


Physical exam

Physical examination may sometimes reveal hypotension, low blood pressure, tachycardia, high heart rate, or low Oxygenation (medical), oxygen saturation. The respiratory rate may be faster than normal, and this may occur a day or two before other signs. Examination of the chest may be normal, but it may show decreased expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchus, bronchial breathing and are heard on auscultation with a stethoscope. Crackles (rales) may be heard over the affected area during inhalation, inspiration. Percussion (medicine), Percussion may be dulled over the affected lung, and increased, rather than decreased, vocal resonation, vocal resonance distinguishes pneumonia from a pleural effusion.


Imaging

A chest radiograph is frequently used in diagnosis. In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain. If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended. Findings do not always match the severity of disease and do not reliably separate between bacterial and viral infection. X-ray presentations of pneumonia may be classified as lobar pneumonia, bronchopneumonia, lobular pneumonia, and interstitial pneumonia. Bacterial, community-acquired pneumonia classically show lung consolidation of one Bronchopulmonary segment, lung segmental lobe, which is known as lobar pneumonia. However, findings may vary, and other patterns are common in other types of pneumonia. Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side. Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation. Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to interpret in the obesity, obese or those with a history of lung disease. Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiographs can increase the diagnostic accuracy of lung consolidation and pleural effusion. A CT scan can give additional information in indeterminate cases. CT scans can also provide more details in those with an unclear chest radiograph (for example occult pneumonia in
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
) and can exclude pulmonary embolism and fungal pneumonia and detect
lung abscess Lung abscess is a type of liquefactive necrosisLiquefactive necrosis (or colliquative necrosis) is a type of necrosis which results in a transformation of the tissue into a liquid viscous mass.Robbins and Cotran: Pathologic Basis of Disease, 8th Ed ...
in those who are not responding to treatments. However, CT scans are more expensive, have a higher dose of radiation, and cannot be done at bedside. Lung ultrasound may also be useful in helping to make the diagnosis. Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings. It may be more accurate than chest X-ray. File:UOTW 34 - Ultrasound of the Week 1.webm, Pneumonia seen by ultrasound File:UOTW 34 - Ultrasound of the Week 2.webm, Pneumonia seen by ultrasound File:UOTW 34 - Ultrasound of the Week 3.jpg, Pneumonia seen by ultrasound File:RtPneuKidMark.png, Right middle lobe pneumonia in a child as seen on plain X-ray


Microbiology

In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management. For people who do not respond to treatment, sputum culture should be considered, and culture for ''Mycobacterium tuberculosis'' should be carried out in persons with a chronic productive cough. Microbiological evaluation is also indicated in severe pneumonia, alcoholism, asplenia, immunosuppression, HIV infection, and those being empirically treated for MRSA of pseudomonas. Although positive blood culture and pleural fluid culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of colonisation (biology), colonisation of respiratory tract. Testing for other specific organisms may be recommended during outbreaks, for public health reasons. In those hospitalized for severe disease, both sputum and blood cultures are recommended, as well as testing the urine for antigens to ''Legionella'' and ''Streptococcus''. Viral infections, can be confirmed via detection of either the virus or its antigens with Viral culture, culture or polymerase chain reaction (PCR), among other techniques. ''Mycoplasma'', ''Legionella'', ''Streptococcus'', and ''Chlamydia'' can also be detected using PCR techniques on bronchoalveolar lavage and nasopharyngeal swab. The causative agent is determined in only 15% of cases with routine microbiological tests.


Classification

Pneumonitis refers to lung
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of pulmonary consolidation. Pneumonia is most commonly classified by where or how it was acquired: Community-acquired pneumonia, community-acquired, aspiration pneumonia, aspiration, healthcare-associated pneumonia, healthcare-associated, hospital-acquired pneumonia, hospital-acquired, and
ventilator-associated pneumonia Ventilator-associated pneumonia (VAP) is a type of lung infection that occurs in people who are on mechanical ventilation breathing machines in hospitals. As such, VAP typically affects critically ill persons that are in an intensive care unit (IC ...
. It may also be classified by the area of the lung affected: lobar pneumonia, bronchial pneumonia and acute interstitial pneumonia; or by the causative organism. Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe. The setting in which pneumonia develops is important to treatment, as it correlates to which pathogens are likely suspects, which mechanisms are likely, which antibiotics are likely to work or fail, and which complications can be expected based on the person's health status.


Community

Community-acquired pneumonia (CAP) is acquired in the community, outside of health care facilities. Compared with healthcare-associated pneumonia, it is less likely to involve multiple drug resistance, multidrug-resistant bacteria. Although the latter are no longer rare in CAP, they are still less likely.


Healthcare

Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system, including hospitals, outpatient clinics, nursing homes, dialysis centers, chemotherapy treatment, or home care. HCAP is sometimes called MCAP (medical care–associated pneumonia). People may become infected with pneumonia in a hospital; this is defined as pneumonia not present at the time of admission (symptoms must start at least 48 hours after admission). It is likely to involve hospital-acquired infections, with higher risk of multidrug-resistant pathogens. People in a hospital often have other medical conditions, which may make them more susceptible to pathogens in the hospital. Ventilator-associated pneumonia occurs in people breathing with the help of
mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilationIntermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses p ...
. Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after endotracheal intubation.


Differential diagnosis

Several diseases can present with similar signs and symptoms to pneumonia, such as:
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
,
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
, pulmonary edema, bronchiectasis, lung cancer, and pulmonary emboli. Unlike pneumonia, asthma and COPD typically present with
wheezing A wheeze is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed (for example narrowing of the lower respiratory tract ...
, pulmonary edema presents with an abnormal electrocardiogram, cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli present with acute onset sharp chest pain and
shortness of breath Shortness of breath (SOB), also known as dyspnea (BrE British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificat ...
. Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from acute heart failure. Pulmonary infiltrates that resolved after giving
mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilationIntermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses p ...
should point to heart failure and atelectasis rather than pneumonia. For recurrent pneumonia, underlying lung cancer, metastasis,
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
, a foreign bodies, immunosuppression, and hypersensitivity should be suspected.


Prevention

Prevention includes vaccination, environmental measures, and appropriate treatment of other health problems. It is believed that, if appropriate preventive measures were instituted globally, mortality among children could be reduced by 400,000; and, if proper treatment were universally available, childhood deaths could be decreased by another 600,000.


Vaccination

Vaccination prevents against certain bacterial and viral pneumonias both in children and adults. Influenza vaccines are modestly effective at preventing symptoms of influenza, The Center for Disease Control and Prevention (CDC) recommends yearly influenza vaccination for every person 6 months and older. Immunizing health care workers decreases the risk of viral pneumonia among their patients. Vaccinations against ''
Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), b ...

Haemophilus influenzae
'' and ''
Streptococcus pneumoniae ''Streptococcus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...

Streptococcus pneumoniae
'' have good evidence to support their use. There is strong evidence for vaccinating children under the age of 2 against ''Streptococcus pneumoniae'' (pneumococcal conjugate vaccine). Vaccinating children against ''Streptococcus pneumoniae'' has led to a decreased rate of these infections in adults, because many adults acquire infections from children. A Pneumococcal polysaccharide vaccine, ''Streptococcus pneumoniae'' vaccine is available for adults, and has been found to decrease the risk of invasive pneumococcal disease by 74%, but there is insufficient evidence to suggest using the pneumococcal vaccine to prevent pneumonia or death in the general adult population. The CDC recommends that young children and adults over the age of 65 receive the pneumococcal vaccine, as well as older children or younger adults who have an increased risk of getting pneumococcal disease. The pneumococcal vaccine has been shown to reduce the risk of community acquired pneumonia in people with
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease The lungs are the primary Organ (anatomy), organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammal ...
, but does not reduce mortality or the risk of hospitalization for people with this condition. People with COPD are recommended by a number of guidelines to have a pneumococcal vaccination. Other vaccines for which there is support for a protective effect against pneumonia include Pertussis vaccine, pertussis, varicella vaccine, varicella, and Measles vaccine, measles.


Medications

When influenza outbreaks occur, medications such as amantadine or rimantadine may help prevent the condition, but they are associated with side effects. Zanamivir or oseltamivir decrease the chance that people who are exposed to the virus will develop symptoms; however, it is recommended that potential side effects are taken into account.


Other

Smoking cessation and reducing indoor air quality, indoor air pollution, such as that from cooking indoors with wood, crop residues or feces, dung, are both recommended. Smoking appears to be the single biggest risk factor for pneumococcal pneumonia in otherwise-healthy adults. Hand hygiene and coughing into one's sleeve may also be effective preventative measures. Wearing surgical masks by the sick may also prevent illness. Appropriately treating underlying illnesses (such as HIV/AIDS, diabetes mellitus, and
malnutrition Malnutrition is 'a state of nutrition in which a deficiency or excess (or imbalance) of energy, protein and other nutrients causes measurable adverse effect on tissue and body form (body shape, size and composition) and function and clinical ou ...
) can decrease the risk of pneumonia. In children less than 6 months of age, exclusive breast feeding reduces both the risk and severity of disease. In people with HIV/AIDS and a CD4 count of less than 200 cells/uL the antibiotic trimethoprim/sulfamethoxazole decreases the risk of ''Pneumocystis pneumonia'' and is also useful for prevention in those that are immunocompromised but do not have HIV. Testing pregnant women for Group B Streptococcus and ''Chlamydia trachomatis'', and administering
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
treatment, if needed, reduces rates of pneumonia in infants; preventive measures for HIV transmission from mother to child may also be efficient. Suctioning the mouth and throat of infants with meconium-stained amniotic fluid has not been found to reduce the rate of
aspiration pneumonia Aspiration pneumonia is a type of pneumonia, lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complication ...
and may cause potential harm, thus this practice is not recommended in the majority of situations. In the frail elderly good oral health care may lower the risk of aspiration pneumonia. Zinc supplementation in children 2 months to five years old appears to reduce rates of pneumonia. For people with low levels of vitamin C in their diet or blood, taking vitamin C supplements may be suggested to decrease the risk of pneumonia, although there is no strong evidence of benefit. There is insufficient evidence to recommend that the general population take vitamin C to prevent pneumonia. For adults and children in the hospital who require a respirator, there is no strong evidence indicating a difference between heat and moisture exchangers and Humidifier, heated humidifiers for preventing pneumonia. There is no good evidence that one approach to mouth care is better than others in preventing nursing home acquired pneumonia. There is tentative evidence that laying flat on the back compared to semi-raised increases pneumonia risks in people who are intubated.


Management

Antibiotics by mouth, rest, simple analgesics, and fluids usually suffice for complete resolution. However, those with other medical conditions, the elderly, or those with significant trouble breathing may require more advanced care. If the symptoms worsen, the pneumonia does not improve with home treatment, or complications occur, hospitalization may be required. Worldwide, approximately 7–13% of cases in children result in hospitalization, whereas in the developed world between 22 and 42% of adults with community-acquired pneumonia are admitted. The CURB-65 score is useful for determining the need for admission in adults. If the score is 0 or 1, people can typically be managed at home; if it is 2, a short hospital stay or close follow-up is needed; if it is 3–5, hospitalization is recommended. In children those with Dyspnea, respiratory distress or oxygen saturations of less than 90% should be hospitalized. The utility of chest physiotherapy in pneumonia has not yet been determined. Over-the-counter cough medicine has not been found to be effective, nor has the use of zinc supplementation, zinc in children. There is insufficient evidence for mucolytics. There is no strong evidence to recommend that children who have non-measles related pneumonia take vitamin A supplements. Vitamin D, as of 2018 is of unclear benefit in children. Pneumonia can cause severe illness in a number of ways, and pneumonia with evidence of organ dysfunction may require intensive care unit admission for observation and specific treatment. The main impact is on the respiratory and the circulatory system. Respiratory failure not responding to normal oxygen therapy may require heated humidified high-flow therapy delivered through nasal cannulae, non-invasive ventilation, or in severe cases Mechanical ventilation, invasive ventilation through an endotracheal tube. Regarding circulatory problems as part of
sepsis Sepsis is a life-threatening condition that arises when the body's response to infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction ...
, evidence of poor blood flow or low blood pressure is initially treated with 30 ml/kg of crystalloid solution, crystalloid infused intravenously. In situations where fluids alone are ineffective, Antihypotensive agent, vasopressor medication may be required. For adults with moderate or severe acute respiratory distress syndrome (ARDS) undergoing mechanical ventilation, there is a reduction in mortality when people proning, lay on their front for at least 12 hours a day. However, this increases the risk of endotracheal tube obstruction and pressure sores.


Bacterial

Antibiotics improve outcomes in those with bacterial pneumonia. The first dose of antibiotics should be given as soon as possible. Increased use of antibiotics, however, may lead to the development of Antimicrobial resistance, antimicrobial resistant strains of bacteria. Antibiotic choice depends initially on the characteristics of the person affected, such as age, underlying health, and the location the infection was acquired. Antibiotic use is also associated with side effects such as nausea, diarrhea, dizziness, taste distortion, or headaches. In the UK, Empiric therapy, treatment before culture results with amoxicillin is recommended as the first line for
community-acquired pneumonia Community-acquired pneumonia (CAP) refers to pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of ...
, with doxycycline or clarithromycin as alternatives. In North America, amoxicillin, doxycycline, and in some areas a macrolide (such as azithromycin or erythromycin) is the first-line outpatient treatment in adults. In children with mild or moderate symptoms, amoxicillin taken by mouth is the first line. The use of fluoroquinolones in uncomplicated cases is discouraged due to concerns about side-effects and generating resistance in light of there being no greater benefit. For those who require hospitalization and caught their pneumonia in the community the use of a β-lactam such as cephazolin plus macrolide such as azithromycin is recommended. A fluoroquinolone may replace azithromycin but is less preferred. Antibiotics by mouth and by injection appear to be similarly effective in children with severe pneumonia. The duration of treatment has traditionally been seven to ten days, but increasing evidence suggests that shorter courses (3–5 days) may be effective for certain types of pneumonia and may reduce the risk of antibiotic resistance. For pneumonia that is associated with a ventilator caused by non-fermenting Gram-negative bacilli (NF-GNB), a shorter course of antibiotics increases the risk that the pneumonia will return. Recommendations for hospital-acquired pneumonia include third- and fourth-generation cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and vancomycin. These antibiotics are often given intravenous therapy, intravenously and used in combination. In those treated in hospital, more than 90% improve with the initial antibiotics. For people with ventilator-acquired pneumonia, the choice of antibiotic therapy will depend on the person's risk of being infected with a strain of bacteria that is Multi-drug resistant bacteria, multi-drug resistant. Once clinically stable, intravenous antibiotics should be switched to oral antibiotics. For those with ''Methicillin resistant Staphylococcus aureus'' (MRSA) or ''Legionella'' infections, prolonged antibiotics may be beneficial. The addition of corticosteroids to standard antibiotic treatment appears to improve outcomes, reducing death and morbidity for adults with severe community acquired pneumonia, and reducing death for adults and children with non-severe community acquired pneumonia. A 2017 review therefore recommended them in adults with severe community acquired pneumonia. A 2019 guideline however recommended against their general use, unless refractory shock was present. Side effects associated with the use of corticosteroids include high blood sugar. There is some evidence that adding corticosteroids to the standard PCP pneumonia treatment may be beneficial for people who are infected with HIV. The use of granulocyte colony stimulating factor (G-CSF) along with antibiotics does not appear to reduce mortality and routine use for treating pneumonia is not supported by evidence.


Viral

Neuraminidase inhibitors may be used to treat viral pneumonia caused by influenza viruses (influenza A and influenza B). No specific antiviral drug, antiviral medications are recommended for other types of community acquired viral pneumonias including SARS, SARS coronavirus,
adenovirus Adenoviruses (members of the family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to ma ...

adenovirus
, hantavirus, and
parainfluenza Human parainfluenza viruses (HPIVs) are the viruses that cause human parainfluenza. HPIVs are a paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor exclud ...
virus. Influenza A may be treated with rimantadine or amantadine, while influenza A or B may be treated with oseltamivir, zanamivir or peramivir. These are of most benefit if they are started within 48 hours of the onset of symptoms. Many strains of H5N1 influenza A, also known as avian influenza or "bird flu", have shown resistance to rimantadine and amantadine. The use of antibiotics in viral pneumonia is recommended by some experts, as it is impossible to rule out a complicating bacterial infection. The British Thoracic Society recommends that antibiotics be withheld in those with mild disease. The use of corticosteroids is controversial.


Aspiration

In general, Chemical pneumonitis, aspiration pneumonitis is treated conservatively with antibiotics indicated only for
aspiration pneumonia Aspiration pneumonia is a type of pneumonia, lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complication ...
. The choice of antibiotic will depend on several factors, including the suspected causative organism and whether pneumonia was acquired in the community or developed in a hospital setting. Common options include clindamycin, a combination of a beta-lactam antibiotic and metronidazole, or an aminoglycoside. Corticosteroids are sometimes used in aspiration pneumonia, but there is limited evidence to support their effectiveness.


Follow-up

The British Thoracic Society recommends that a follow-up chest radiograph be taken in people with persistent symptoms, smokers, and people older than 50. American guidelines vary, from generally recommending a follow-up chest radiograph to not mentioning any follow-up.


Prognosis

With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. It often takes a few weeks before most symptoms resolve. X-ray findings typically clear within four weeks and mortality is low (less than 1%). In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%. Pneumonia is the most common nosocomial infection, hospital-acquired infection that causes death.Murray and Nadel (2010). Chapter 32. Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis. If pneumonia deteriorates after 72 hours, it could be due to nosocomial infection or excerbation of other underlying comorbidities. About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurological disorders, or due to new onset of pneumonia. Complications may occur in particular in the elderly and those with underlying health problems. This may include, among others: empyema,
lung abscess Lung abscess is a type of liquefactive necrosisLiquefactive necrosis (or colliquative necrosis) is a type of necrosis which results in a transformation of the tissue into a liquid viscous mass.Robbins and Cotran: Pathologic Basis of Disease, 8th Ed ...
, bronchiolitis obliterans, acute respiratory distress syndrome,
sepsis Sepsis is a life-threatening condition that arises when the body's response to infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction ...
, and worsening of underlying health problems.Cunha (2010). pp. 6–18.


Clinical prediction rules

Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia. These rules are often used to decide whether to hospitalize the person. * Pneumonia severity index (or ''PSI Score'') * CURB-65 score, which takes into account the severity of symptoms, any underlying diseases, and age


Pleural effusion, empyema, and abscess

In pneumonia, a pleural effusion, collection of fluid may form in the pleural cavity, space that surrounds the lung. Occasionally, microorganisms will infect this fluid, causing an pleural empyema, empyema. To distinguish an empyema from the more common simple parapneumonic effusion, the fluid may be collected with a needle (thoracentesis), and examined. If this shows evidence of empyema, complete drainage of the fluid is necessary, often requiring a chest tube, drainage catheter. In severe cases of empyema, Decortication, surgery may be needed. If the infected fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity. If the fluid is sterile, it must be drained only if it is causing symptoms or remains unresolved. In rare circumstances, bacteria in the lung will form a pocket of infected fluid called a
lung abscess Lung abscess is a type of liquefactive necrosisLiquefactive necrosis (or colliquative necrosis) is a type of necrosis which results in a transformation of the tissue into a liquid viscous mass.Robbins and Cotran: Pathologic Basis of Disease, 8th Ed ...
. Lung abscesses can usually be seen with a chest X-ray but frequently require a chest CT scan to confirm the diagnosis. Abscesses typically occur in
aspiration pneumonia Aspiration pneumonia is a type of pneumonia, lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complication ...
, and often contain several types of bacteria. Long-term antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a surgery, surgeon or Interventional radiology, radiologist.


Respiratory and circulatory failure

Pneumonia can cause respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response. The lungs quickly fill with fluid and become stiff. This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, may require long periods of
mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilationIntermittent Mandatory Ventilation (IMV) refers to any mode of mechanical ventilation where a regular series of breaths are scheduled but the ventilator senses p ...
for survival. Other causes of circulatory failure are hypoxemia,
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
, and increased coagulability. Sepsis is a potential complication of pneumonia but usually occurs in people with poor immunity or hyposplenism. The organisms most commonly involved are ''Streptococcus pneumoniae'', ''Haemophilus influenzae'', and ''Klebsiella pneumoniae''. Other causes of the symptoms should be considered such as a myocardial infarction or a pulmonary embolism.Cunha (2010). pp. 250–51.


Epidemiology

Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world. It is a major cause of death among all age groups resulting in 4 million deaths (7% of the world's total death) yearly. Rates are greatest in children less than five, and adults older than 75 years. It occurs about five times more frequently in the developing world than in the developed world. Viral pneumonia accounts for about 200 million cases. In the United States, as of 2009, pneumonia is the 8th leading cause of death.


Children

In 2008, pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world). In 2010, it resulted in 1.3 million deaths, or 18% of all deaths in those under five years, of which 95% occurred in the developing world. Countries with the greatest burden of disease include India (43 million), China (21 million) and Pakistan (10 million). It is the leading cause of death among children in low income countries. Many of these deaths occur in the neonatal, newborn period. The World Health Organization estimates that one in three newborn infant deaths is due to pneumonia. Approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available. In 2011, pneumonia was the most common reason for admission to the hospital after an emergency department visit in the U.S. for infants and children.


History

Pneumonia has been a common disease throughout human history. The word is from Greek πνεύμων (pneúmōn) meaning "lung". The symptoms were described by Hippocrates (c. 460–370 BC): "Peripneumonia, and pleuritic affections, are to be thus observed: If the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... When pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand."Hippocrates ''On Acute Diseases'' s:On Regimen in Acute Diseases, wikisource link However, Hippocrates referred to pneumonia as a disease "named by the ancients". He also reported the results of surgical drainage of empyemas. Maimonides (1135–1204 AD) observed: "The basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking pleuritic pain in the side, short rapid breaths, serrated pulse and cough."Maimonides, ''Fusul Musa'' ("''Pirkei Moshe''"). This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the Middle Ages into the 19th century. Edwin Klebs was the first to observe bacteria in the airways of persons having died of pneumonia in 1875. Initial work identifying the two common bacterial causes, ''Streptococcus pneumoniae'' and ''Klebsiella pneumoniae'', was performed by Carl Friedländer and Albert Fraenkel (1848–1916), Albert Fraenkel in 1882 and 1884, respectively. Friedländer's initial work introduced the Gram staining, Gram stain, a fundamental laboratory test still used today to identify and categorize bacteria. Christian Gram's paper describing the procedure in 1884 helped to differentiate the two bacteria, and showed that pneumonia could be caused by more than one microorganism. In 1887, Jaccond demonstrated pneumonia may be caused by opportunistic bacteria always present in the lung. Sir William Osler, known as "the father of modern medicine", appreciated the death and disability caused by pneumonia, describing it as the "captain of the men of death" in 1918, as it had overtaken
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
as one of the leading causes of death in this time. This phrase was originally coined by John Bunyan in reference to "consumption" (tuberculosis). Osler also described pneumonia as "the old man's friend" as death was often quick and painless when there were much slower and more painful ways to die. Viral pneumonia was first described by Hobart Reimann in 1938. Reimann, Chairman of the Department of Medicine at Thomas Jefferson University, Jefferson Medical College, had established the practice of routinely typing the pneumococcal organism in cases where pneumonia presented. Out of this work, the distinction between viral and bacterial strains was noticed. Several developments in the 1900s improved the outcome for those with pneumonia. With the advent of penicillin and other antibiotics, modern surgical techniques, and intensive care in the 20th century, mortality from pneumonia, which had approached 30%, dropped precipitously in the developed world. Vaccination of infants against ''
Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), b ...

Haemophilus influenzae
'' type B began in 1988 and led to a dramatic decline in cases shortly thereafter. Vaccination against ''Streptococcus pneumoniae'' in adults began in 1977, and in children in 2000, resulting in a similar decline.


Society and culture


Awareness

Due to the relatively low awareness of the disease, 12 November was declared as the annual World Pneumonia Day, a day for concerned citizens and policy makers to take action against the disease, in 2009.


Costs

The global economic cost of community-acquired pneumonia has been estimated at $17 billion annually. Other estimates are considerably higher. In 2012 the estimated aggregate costs of treating pneumonia in the United States were $20 billion; the median cost of a single pneumonia-related hospitalization is over $15,000. According to data released by the Centers for Medicare and Medicaid Services, average 2012 hospital charges for inpatient treatment of uncomplicated pneumonia in the U.S. were $24,549 and ranged as high as $124,000. The average cost of an emergency room consult for pneumonia was $943 and the average cost for medication was $66. Aggregate annual costs of treating pneumonia in Europe have been estimated at €10 billion.


References

Footnotes Citations


Bibliography

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External links

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