COVID-19: Health Alert #7
Antibody Testing for SARS-CoV-2 in Wisconsin:
Recommendations and Reporting Requirements
Bureau of Communicable Diseases, May 1, 2020
A growing number of serologic tests for detection of IgG and/or IgM antibodies against SARS-CoV-2 have received FDA approval under an Emergency Use Authorization and are now commercially available. The sensitivity and specificity of these tests are variable, and the results should be interpreted with caution.
While SARS-CoV-2 antibody tests can provide evidence of past COVID-19 infection, DHS recommends against using these tests for diagnosis of active infection. Diagnosis of acute infection should be based on molecular detection methods such as PCR.
If antibody testing is obtained for the purpose of documenting past infection, all positive anti-SARS-CoV-2 IgM, IgG or total antibody test results should be reported to public health via the Wisconsin Electronic Disease Surveillance System (WEDSS). Negative antibody test results should not be reported to public health.
It is not currently known whether or to what degree the presence of SARS-CoV-2 antibodies confers protection from future infection. As such, it is inappropriate to use the results of antibody testing for the basis of any decisions related to returning to work or infection control practices within health care or other workplace settings.
The Wisconsin Department of Health Services has been reviewing emerging data and international guidance related to the use of serologic (antibody-based) testing for COVID-19. Over the past month the market has flooded with a multitude of different antibody tests for COVID-19; they have variable performance, target different viral antigens, and may not be comparable to each other.
As more data are gathered in the coming months and the performance characteristics of approved tests are better understood, serologic tests will play an important role in determining the prevalence of COVID-19 on a population level, and may inform local and state wide epidemiologic studies and future modeling efforts.
Except in limited situations, antibody testing should not play a role in making a diagnosis of COVID-19. SARS-CoV-2 antibody tests have a low sensitivity in early infection which makes serologic testing unhelpful in ruling out COVID-19 in symptomatic patients. There may be a role for supporting diagnosis for patients who present late in the course of illness who have a very low viral load below the detection limit of RT-PCR assays, or when lower respiratory tract sampling is not possible.
While antibody tests should not be relied on for diagnosis, positive SARS-CoV-2 antibody test results must be reported to public health. The preferred mechanism for reporting is the Wisconsin Electronic Disease Surveillance System (WEDSS). Patients who have pending antibody tests do NOT need to be reported to public health while results are pending. However, positive antibody test results must be reported, negative test results do not need to be reported.
As a reminder, all patients with suspected COVID-19 infections must be reported to public health. This means patients with a pending molecular amplification test (e.g. PCR, NAAT) should be reported to public health while laboratory results are pending and both positive and negative test results should be reported.
There is understandable interest in the topic of SARS-CoV-2 antibodies as a possible marker of immunity and protection from future infection. Unfortunately, at this point in time, we do not know whether or not the presence of detectable antibodies equates to immunity, and even if it does, what level of antibody is needed or how long the immunity lasts. Until these questions are answered, serologic testing should not be used as a gate-keeper for employment, and should not be used to modify any practices related to personal protective equipment in health care settings.
Several online resources are now available for further information on this topic:
Ryan Westergaard, MD, PhD, MPH Chief Medical Officer and State Epidemiologist for Communicable Diseases Wisconsin Department of Health Services