Viral disease testing is the use of a variety of testing techniques for a variety of purposes, including diagnosing conditions, assessing immunity and understanding disease prevalence. The primary approaches include DNA/

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

tests, serological tests and antigen tests.

History

COVID-19

In March 2020, Abbott received

emergency use authorization An Emergency Use Authorization (EUA) in the United States is an authorization granted to the Food and Drug Administration (FDA) under sections of the Federal Food, Drug, and Cosmetic Act as added to and amended by various Act of Congress, Acts of ...

(EUA) for its isothermal nucleic acid test for COVID-19. It produces test results in 5 minutes using its ID NOW portable testing system. It also received EUA for its m2000-based laboratory nucleic acid test for COVID-19. In April 2020, Abbott received EUA for its ARCHITECT IgG laboratory antibody test for COVID-19. Also in April, Abbott's ID NOW test was reported to have sensitivity of 85.2%. A later study found sensitivity of only 52%, inducing the FDA to issue an alert. A different study found sensitivity of 91%. The UK spent $20 million for antibody tests that proved flawed. In May 2020, a rapid antigen test from Quidel Corporation received EUA for detecting SARS-CoV-2. Test results were said to be available at

point of care Clinical point of care (POC) is the point in time when clinicians deliver healthcare products and services to patients at the time of care. Clinical documentation Clinical documentation is a record of the critical thinking and judgment of a health ...

within 15 minutes. Sensitivity is 85%. Also in May 2020, a CRISPR genetic test was approved for emergency use that claimed 100% selectivity and 97.5% sensitivity. That month Abbott received EUA for its Alinity antibody test for COVID-19. The company claimed 100% sensitivity and 99.6% specificity for patients tested 14 days after symptoms began. Another review found that the accuracy of PCR tests depended on the interval between the infection and the test. Immediately after infection, the sensitivity was 0, rising to 80% after three days and then declining thereafter. In May 2020 the FDA withdrew approval for 29 of 41 antibody tests for which it had given EUAs.

Types

DNA/RNA tests

Tests for viral DNA can look for either DNA or

. They typically use

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, ...

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) t ...

s to multiply the amount of genetic material in a small sample into an amount that is measurable. The genetic material is generally taken from the nose/sinus. One study found clinical sensitivity was found to range from 66 to 80%. Another found accuracy of 70%. A newer form uses

CRISPR CRISPR () (an acronym for clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. These sequences are derived from DNA fragments of bacte ...

to produce a test result without requiring lab equipment. The test reacts with genetic material to produce a visible signal without requiring amplification.

Serological tests

Serological tests look for the presence of

antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

in a test sample. Antibodies are materials that the body produces to fight off an infection. The primary antibodies sought in viral testing are

IgE Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isotype") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε c ...

and

IgG Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG ...

Rapid antigen tests

A rapid antigen test quickly searches for antigens, protein fragments that are found on the surface of or within a virus. Antigen tests can be analyzed within a few minutes. Antigen tests are less accurate than PCR tests. It has a low false positive rate, but a higher false negative rate. A negative test result may require confirmation with a PCR test. Advocates claim that antigen tests are less expensive and can be scaled up more rapidly than PCR tests. Antigen tests are available for a variety of conditions, including

streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs ...

influenza Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms ...

giardia ''Giardia'' ( or ) is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada that colonise and reproduce in the small intestines of several vertebrates, causing the disease giardiasis. Their life cycle alternates between ...

Ebola Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after becom ...

and ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is though ...

''. Antigens can be detected via blood, urine or stool.

Imaging

Imaging such as computerized tomography can be used to inform a diagnostic process. CT scans are considerably more expensive than nucleic acid tests and involve a small dose of radiation. For COVID-19, they are seen as the most accurate diagnostic tool, because the disease creates patchy "ground glass" areas in the lungs that are revealed by a scan. One study found 97% sensitivity.

Accuracy

Accuracy is measured in terms of specificity and selectivity. Test errors can come false positives (the test is positive, but the virus is not present) or false negatives, (the test is negative, but the virus is present).

Sensitivity

Sensitivity indicates whether the test accurately identifies whether the virus is or is present. A 90% sensitive test will correctly identify 90% of infections, leaving 10% with a false negative result.

Specificity

Specificity indicates how well-targeted the test is to the virus in question. Highly specific tests pick up only the virus in question. Non-selective tests pick up other viruses as well. A 90% specific test will correctly identify 90% of those who are uninfected, leaving 10% with a false positive result.

References

External links

* {{Cite web, title=Comparing RT-PCR and Chest CT for Diagnosing COVID-19, url=https://www.mdmag.com/medical-news/comparing-rt-pcr-and-chest-ct-for-diagnosing-covid19, website=HCPLive®, access-date=2020-05-31 Viral diseases Infectious disease blood tests COVID-19 testing