This page provides a brief overview of COVID-19 testing to inform decision-making for first responders, including emergency medical service (EMS), fire and rescue, law enforcement, and 911 telecommunicators.
SARS-CoV-2 is the virus that causes the disease COVID-19. The Food and Drug Administration (FDA) is the U.S. government entity responsible for regulating medical devices, including tests and devices like those being used to detect SARS-CoV-2.
Because of the public health emergency caused by a novel coronavirus, the FDA has issued multiple Emergency Use Authorizations (EUA) for various types of medical devices, including tests. Final validation of these tests still needs to be completed through normal FDA clearance processes and receive approval by the FDA under the traditional marketing pathways approval processes. A list of tests with EUAs is available at EUA Information: FDA.gov.
Molecular diagnostic tests look for evidence of an active infection by detecting either the genetic material of the pathogen or a unique marker of it. This type of test detects signs of the virus's genetic material.
One type of molecular testing uses a reverse transcriptase polymerase chain reaction (RT-PCR) for pathogen detection. This method requires only a small sample size of the pathogen. It amplifies segments of the virus' genetic code and replicates it in order to show its presence and allow it to be more easily detected. A positive result indicates the presence of actual infectious viral material in the body. Test samples are usually obtained from humans using a special nasal swab designed for this purpose.
These results, however, cannot alone determine if the pathogen remains viable or is dead and no longer infective. The presence of such material does not necessarily indicate if the patient is infectious but simply that such material is there. For provider safety, patients with a positive test should be presumed infectious.
The antigen diagnostic tests quickly detect fragments of pathogen proteins found on or within the virus from human testing samples, often from a swab of the nasopharyngeal cavity. Antigen tests may not detect all active infections. These tests are very specific for the virus but are often not as sensitive as molecular RT-PCR tests because of the certainty of positive samples used to develop the actual test.
Positive results from antigen tests are highly accurate but there is also a higher chance of false negatives. As a result, negative results do not rule out infection. Until well-validated antigen testing is available, negative results from this approach may warrant confirmatory testing using a molecular test. An antigen test may need to be confirmed with a RT-PCR test prior to making treatment decisions to help prevent the possible spread of the virus due to a false negative.
Serology tests look for the presence of antibodies, which are specific proteins made in response to an infection as part of the body's attempt to fight that infection. A serology test does not specifically indicate current (active) disease.
It is important to remember that development of antibodies takes some time, usually weeks, after exposure to the infection. There are also different types of antibodies (IgG and IgM) that are developed and can be tested for individually.
Depending on when someone was infected and the timing of the test, antibodies may not have developed in sufficient quantities to be detected by the test. We currently don't know if detection of antibodies, and at what level, indicates immunity and/or protection, from a future exposure. Similarly, there is another concern that any detected antibodies may instead reflect other strains of more commonly occurring coronaviruses, such as variations of the common cold.
No test is 100% accurate 100% of the time.
Specificity is a measure of a test's ability to correctly generate a negative result for people who don't have the condition that's being tested for. This is known as the “true negative” rate.
A high-specificity test will correctly rule out almost everyone who doesn't have the disease when the test is negative and won't generate a high percentage of false-positive results. For example, a test with 90% specificity will correctly return a negative result for 90% of people who don't have the disease but will return a positive result – a false-positive – for 10% of the people who don't have the disease and should have tested negative.
Sensitivity is a measure of how often a test correctly generates a positive result for people who have the condition that's being tested for. This is known as the “true positive” rate.
A test that's highly sensitive will identify almost everyone who has the disease and not generate many false-negative results. For example, a test with 90% sensitivity will correctly return a positive result for 90% of people who have the disease but will return a negative result – a false-negative – for 10% of the people who have the disease.
A variety of tests have not been reviewed by FDA but may be purchased to test for COVID-19. The concern with false negatives from these tests relates to the higher potential for future transmissions whereas the concern for false positives relates to unnecessary diagnostic or medical procedures for the patent and wasted PPE use for the provider. A false negative result could lead to additional exposure to contacts of the patient, including first responders and EMS personnel.
This guidance was developed by the Federal Healthcare Resilience Task Force (HRTF). The HRTF is leading the development of a comprehensive strategy for the U.S. healthcare system to facilitate resiliency and responsiveness to the threats posed by COVID-19. The Task Force's EMS/Pre-Hospital Team is comprised of public and private-sector EMS and 911 experts from a wide variety of agencies and focuses on responding to the needs of the pre-hospital community. This team is composed of subject matter experts from NHTSA OEMS, CDC, FEMA, USFA, U.S. Army, USCG and non-federal partners representing stakeholder groups and areas of expertise. Through collaboration with experts in related fields, the team develops practical resources for field providers, supervisors, administrators, medical directors and associations to better respond to the COVID-19 pandemic.
Primary Point of Contact: NHTSA Office of EMS, email@example.com, 202-366-5440