Following updated guidance that recommends people who have tested positive for COVID-19 isolate for five days rather than the previously suggested 10, the U.S. Centers for Disease Control now has a message regarding re-testing: Do it if you want to but be prepared to act based on the result.
According to the CDC, anyone who is suspected or confirmed to have COVID-19 should avoid contact with others for a minimum of five days following the positive test or symptom onset, with “day one” the day following either occurrence. (If you test positive on a Monday, for example, your five-day isolation period would begin on Tuesday and last through Saturday, presuming symptoms have improved and you are without fever for at least 24 hours. Sunday would be the first day out of isolation.)
Less clear was whether someone should wait until they test negative before resuming their normal activities. The CDC does not explicitly endorse re-testing, but now suggests that if the test is positive, people should extend their isolation period to 10 days in total. If it’s negative (or no test is done), people can end isolation but should continue wearing a mask regardless of circumstances (i.e. being in the same household as others) until day 10.
Guidance on re-testing remains ambiguous in large part due to the questions concerning the sensitivity of the rapid at-home test kits, which are believed to be less accurate than the lab-based PCR tests administered by health care providers—and PCR tests can demonstrate a positive result even after a person stops being infectious. The updated guidance seems pointed at people who aren’t comfortable with a five-day isolation period and want to assess their status before resuming normal activities. According to the CDC, people are likely most infectious in the first five days following onset of symptoms or a positive test.
The agency’s isolation guidance has faced criticism for being opaque and the lack of firm recommendation on re-testing is likely to invite more, though rapid at-home kits can be difficult to locate in some regions. Their limited availability may be another reason the CDC has stopped short of advising people use them.