TAG's Q&A: False Negatives Likely in COVID-19 Tests within 3 Days of Exposure

 

Q. I have a worker who had a known exposure to COVID-19. The worker was tested the day after the exposure and results came back negative. Additionally, they do not have any symptoms. Can they come back to work?

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A. No. This is a question that we have been getting more frequently at TAG and we thought it was a good time to revisit a study initially published in pre-print in May 2020.  This widely cited study which looked at data in symptomatic cases, shows that persons tested within two days of exposure are almost 100% likely to test negative using a PCR-based test. This probability of false negatives drops only slightly on Day 3. Unfortunately, a negative test during this time cannot be trusted as accurate. As shown in the diagram, the potential for a false negative (when a test identifies a person as not having COVID-19 but they actually do) drops significantly at Day 4; but, it is still likely to give a false negative. The greatest potential for a true negative is on Day 8, which is 3 days after the typical/average time of symptom onset (Day 5). (In fact, if a person does test positive within a couple days of the supposed exposure, it is likely that that were exposed earlier!)

 

While the data in this study is based on an assessment of symptomatic cases, TAG highly recommends that businesses continue the practice of requiring workers to quarantine for 14 days after an exposure. If they still have no symptoms and test negative on Day 8 following their suspected exposure, TAG recommends that the worker get a medical opinion prior to returning to the workplace.