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 Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

tests, serological tests and antigen tests.

History

COVID-19

In March 2020, Abbott received emergency use authorization (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 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

. They typically use

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobi ...

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

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 (; acronym of clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. Each sequence within an individual prokaryotic CRISPR is d ...

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) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

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 and IgG.

Rapid antigen tests

rapid antigen test A rapid antigen test (RAT), sometimes called a rapid antigen detection test (RADT), antigen rapid test (ART), or wikt:Appendix:Glossary#loosely, loosely just a rapid test, is a rapid diagnostic test suitable for point-of-care testing that directl ...

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 spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs along a sing ...

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 sympto ...

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 be ...

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 in ...

and ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

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

Imaging

Imaging such as

computerized tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

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 A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test res ...

(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 not 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