![Difference between outbreak, endemic, epidemic and pandemic-en](https://upload.wikimedia.org/wikipedia/commons/c/c1/Difference_between_outbreak%2C_endemic%2C_epidemic_and_pandemic-en.png)
In
epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evidenc ...
, an outbreak is a sudden increase in occurrences of a
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 immediately due to any external injury. Diseases are often known to be medical conditions that a ...
when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire continent. The number of cases varies according to the disease-causing agent, and the size and type of previous and existing exposure to the agent. Outbreaks include many
epidemics
An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time.
Epidemics of infectious d ...
, which term is normally only for
infectious diseases
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
, as well as diseases with an environmental origin, such as a water or
foodborne disease
Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food,
as well as prions (the agents of mad cow disease) ...
. They may affect a region in a country or a group of countries.
Pandemics
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic disease with a stable number of in ...
are near-global disease outbreaks when multiple and various countries around the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
are soon infected.
Definition
The terms "outbreak" and "epidemic" have often been used interchangeably. Researchers Manfred S. Green and colleagues propose that the latter term be restricted to larger events, pointing out that ''
Chambers Concise Dictionary'' and ''
Stedman's Medical Dictionary
''Stedman's Medical Dictionary'' is a professional medical dictionary developed for medical students, physicians, researchers, and medical language specialists. Entries include medical terms, abbreviation, acronyms, measurements, and more. Pronunc ...
'' acknowledge this distinction.
Outbreak investigation
![Epidemic curves](https://upload.wikimedia.org/wikipedia/commons/1/15/Epidemic_curves.jpg)
When investigating disease outbreaks, the epidemiology profession has developed a number of widely accepted steps. As described by the United States
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
, these include the following:
* Identify the existence of the outbreak (Is the group of ill persons normal for the time of year, geographic area, etc.?)
* Verify the diagnosis related to the outbreak
* Create a
case definition
In epidemiology, a clinical case definition, a clinical definition, or simply a case definition lists the clinical criteria by which public health professionals determine whether a person's illness is included as a ''case'' in an outbreak investiga ...
to define who/what is included as a case
* Map the spread of the outbreak using
Information technology
Information technology (IT) is the use of computers to create, process, store, retrieve, and exchange all kinds of data . and information. IT forms part of information and communications technology (ICT). An information technology system (I ...
as diagnosis is reported to insurance
* Develop a hypothesis (What appears to be causing the outbreak?)
* Study hypotheses (collect data and perform analysis)
* Refine hypothesis and carry out further study
* Develop and implement control and prevention systems
* Release findings to greater communities
The order of the above steps and relative amount of effort and resources used in each varies from outbreak to outbreak. For example, prevention and control measures are usually implemented very early in the investigation, often before the causative agent is known. In many situations, promoting good hygiene and hand-washing is one of the first things recommended. Other interventions may be added as the investigation moves forward and more information is obtained. Waiting until the end of an investigation to implement prevention and control measures is a sure way to lose ones job. In outbreaks identified through notifiable disease surveillance, reports are often linked to laboratory results and verifying the diagnosis is straight forward. In outbreaks of unknown etiology, determining and verifying the diagnosis can be a significant part of the investigation with respect to time and resources. Several steps are usually going on at any point in time during the investigation. Steps may be repeated. For example, initial case definitions are often established to be intentionally broad but later refined as more is learned about the outbreak. The above list has 9 steps, others have more. Implementing active surveillance to identify additional cases is often added.
Outbreak debriefing and review has also been recognized as an additional final step and iterative process by the Public Health Agency of Canada.
Types
There are several outbreak patterns, which can be useful in identifying the transmission method or source, and predicting the future rate of infection. Each has a distinctive
epidemic curve
An epidemic curve, also known as an epi curve or epidemiological curve, is a statistical chart used in epidemiology to visualise the onset of a disease outbreak. It can help with the identification of the mode of transmission of the disease. It ca ...
, or
histogram
A histogram is an approximate representation of the distribution of numerical data. The term was first introduced by Karl Pearson. To construct a histogram, the first step is to " bin" (or "bucket") the range of values—that is, divide the ent ...
of case infections and deaths.
* Common source – All victims acquire the infection from the same source (e.g. a contaminated water supply).
** Continuous source – Common source outbreak where the exposure occurs over multiple incubation periods
** Point source – Common source outbreak where the exposure occurs in less than one incubation period
* Propagated – Transmission occurs from person to person.
Outbreaks can also be:
* Behavioral risk related (e.g.,
sexually transmitted disease
Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs) and the older term venereal diseases, are infections that are spread by sexual activity, especially vaginal intercourse, anal sex, and oral ...
s, increased risk due to
malnutrition
Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues a ...
)
*
Zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
– The infectious agent is endemic to an animal population, infection is transferred to humans.
Patterns of occurrence are:
*
Endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
– a communicable disease, such as influenza, measles, mumps, pneumonia, colds, viruses, and smallpox, which is characteristic of a particular place, or among a particular group, or area of interest or activity.
*
Epidemic
An epidemic (from Ancient Greek, Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time.
Epidemics ...
– when this disease is found to infect a significantly larger number of people at the same time than is common at that time, and among that population, and may spread through one or several communities.
*
Pandemic
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...
– occurs when an epidemic spreads worldwide.
Condition for Declaring an Outbreak Over
By convention, a communicable disease outbreak is declared over when a period of twice the
incubation period
Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the i ...
of the infectious disease has elapsed without identification of any new case, however, for organisms with a short incubation period (e.g. fewer than ten days), a period of three times the incubation period is preferred.
Outbreak legislation
Outbreak legislation is still in its infancy and not many countries have had a direct and complete set of the provisions.
However, some countries do manage the outbreaks using relevant acts, such as
public health law
Public health law examines the authority of the government at various jurisdictional levels to improve public health, the health of the general population within societal limits and norms. Public health law focuses on the duties of the government ...
.
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
member states are obligated by
International Health Regulations
The International Health Regulations (IHR), first adopted by the World Health Assembly in 1969 and last revised in 2005, are a legally binding rules that only apply to the WHO that is an instrument that aims for international collaboration "to pre ...
to
report outbreaks. WHO member states are holding a special session in November 2021 to consider the
International Treaty for Pandemic Preparedness and Response
International is an adjective (also used as a noun) meaning "between nations".
International may also refer to:
Music Albums
* ''International'' (Kevin Michael album), 2011
* ''International'' (New Order album), 2002
* ''International'' (The T ...
to establish further legal obligations in managing disease outbreaks.
See also
*
1947 New York City smallpox outbreak
The 1947 New York City smallpox outbreak occurred in March 1947 and was declared ended on April 24, 1947. The outbreak marked the largest mass vaccination effort ever conducted for smallpox in America. Within three weeks of the discovery of the o ...
*
1993 Four Corners hantavirus outbreak
The 1993 Four Corners hantavirus outbreak was an outbreak of hantavirus that caused the first known human cases of hantavirus disease in the United States. It occurred within the Four Corners region – the geographic intersection of the U.S. sta ...
*
2003 Midwest monkeypox outbreak
Beginning in May 2003, by July a total of 71 cases of human monkeypox were found in six Midwestern states including Wisconsin (39 cases), Indiana (16), Illinois (12), Kansas (1), Missouri (2), and Ohio (1). The cause of the outbreak was traced ...
*
2007 Yap Islands Zika virus outbreak
*
2014 Democratic Republic of the Congo Ebola virus outbreak
In 2014, an outbreak of Ebola virus disease in the Democratic Republic of the Congo (DRC) occurred. Whole genome sequencing, Genome sequencing has shown that this outbreak was not related to the West Africa Ebola virus epidemic, 2014–15 West Afr ...
*
2019–present coronavirus pandemic by country and territory
*
Superspreading event
A superspreading event (SSEV) is an event in which an infectious disease is spread much more than usual, while an unusually contagious organism infected with a disease is known as a superspreader. In the context of a human-borne illness, a super ...
References
External links
Plague of Suspicion audio hour on media coverage of outbreaks and epidemics
{{Natural disasters
Epidemiology