Health Department

CONTACT INFORMATION: Our administration office at 10777 Main Street in Fairfax is open during regular business hours 8 a.m. - 4:30 p.m., Monday - Friday. Clinic services are not offered at this location.
703-246-2411 TTY 711
10777 Main Street
Fairfax, VA 22030
Gloria Addo-Ayensu, M.D., M.P.H.
Director of Health

Department Resources

COVID-19 Laboratory Updates

Health Advisory

Summary

RT-PCR is the gold-standard viral diagnostic test for SARS-CoV-2, the virus that causes COVID-19. FDA has issued Emergency Use Authorizations (EUA) for four test systems to detect SARS-CoV-2 antigens from respiratory swab specimens. These tests offer rapid, point-of-care diagnosis. The CDC recently released interim guidance for rapid antigen testing for SARS-CoV-2 (https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html). Healthcare providers who use these assays need to be aware of test characteristics and reporting requirements to ensure appropriate diagnosis and public health follow-up of COVID-19 cases in Fairfax County.

Suggested Actions

  • Healthcare providers who use SARS-CoV-2 antigen detection as a component of their COVID-19 diagnostic testing strategy should develop a plan, consistent with CDC and Virginia Department of Health (VDH) guidance, that benefits from the availability of rapid, point-of-care results while appropriately using RT-PCR testing in defined settings to confirm antigen results.
    • Use of rapid antigen tests may be most helpful in the following scenarios: 1) as a diagnostic test for someone who recently has become symptomatic when the viral load generally is highest or for someone who has known exposure to a person with confirmed COVID-19; 2) as a screening test for persons in high-risk congregate settings in which periodic testing can quickly identify persons with SARS-CoV-2 infection to inform prevention and control measures (specific guidance exists for use of point-of-care antigen tests in nursing homes). 
    • A patient with a positive rapid antigen result should be treated as a presumptive case and should be told to stay at home and away from others (self-isolate). Due to the high specificity of these assays, false positive results, particularly in persons who are symptomatic or have a higher probability of infection (e.g., someone exposed to a case), would be uncommon and no confirmation of a positive result is needed. By contrast, a positive test result in someone who is asymptomatic and has a low probability of infection may more likely be a false positive and RT-PCR confirmation may be warranted. Patients should self-isolate pending the result of the confirmatory test.
    • A negative rapid antigen result in a patient who has a higher probability of COVID-19 should be confirmed with an RT-PCR test. Confirmation of a negative test should be done if the result is inconsistent with the clinical context (e.g., a patient who expresses more specific clinical symptoms such as loss of taste or smell) or epidemiologic situation (e.g., household contact with a confirmed case). Again, patients should self-isolate pending the result of the confirmatory test. 
  • As required by law (CARES Act), all SARS-CoV-2 antigen test result must be reported to the local health department. Unlike for RT-PCR, where results are directly transmitted to public health by the laboratory that performs the testing, no such mechanism exists for point-of-care tests. Therefore, healthcare providers should establish reporting processes that ensure rapid antigen test results (both positive and negative) are sent to the Fairfax County Health Department using the following reporting portal through the Virginia Department of Health within 24 hours: https://apps.vdh.virginia.gov/pocreporting/login/login.aspx. Further guidance on this reporting portal can be found in the attached Commissioner’s letter. 

Additional Information

  • Four SARS-CoV-2 antigen diagnostic tests have been authorized by FDA under an EUA (https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency-use-authorizations-medical-devices/vitro-diagnostics-euas#individual-antigen). In data submitted to FDA, test sensitivity varied between 84% and 98% and specificity varied between 97% and 100%. Performance in a clinical setting may differ depending on the quality of the swab, delay between obtaining the swab and testing, and the performance of the test. 
  • Testing can be performed by any CLIA certified lab operating under a Certificate of Waiver, a Certificate of Compliance or Certificate of Accreditation.   
  • Regardless of the viral diagnostic test utilized (RT-PCR or antigen detection), all patients who are tested for SARS-CoV-2 should be told to stay at home and away from others until they receive test results. Further guidance will be provided by public health if the test result is positive.
  • Household contacts of a tested patient whose results are pending should be advised to be alert for subjective fever or other COVID-19 symptoms. If they feel feverish or develop cough or other symptoms during this self-observation period, they should take their temperature, self-isolate, limit contact with others, and seek advice by telephone from their healthcare provider to determine whether medical evaluation and testing are needed.
  • Laboratory testing for SARS-CoV-2 is now recommended for all close contacts (symptomatic and asymptomatic) of confirmed and probable COVID-19 patients. Testing is most effective 5-7 days after exposure to the case. If exposure occurred over several days, test 5-7 days after the most significant exposure following onset of symptoms in the case. Contacts who test negative should still be directed to complete their 14-day quarantine.
  • Healthcare providers who are unable to safely collect specimens for testing can refer patients to the following resource for testing information/locations: https://www.fairfaxcounty.gov/health/novel-coronavirus/coronavirus-covid-19-testing.
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