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While the U.S. Centers for Disease Control and Prevention recommends at least five days of isolation for COVID-19 patients, some people continue to test positive beyond those five days, raising questions about whether they may still be contagious.
According to a Wall Street Journal special report, researchers are not entirely sure how long COVID-19 patients can remain infectious. Nathaniel Hafer, director of operations for the University of Massachusetts Center for Clinical and Translational Science told the newspaper: “It’s still up for debate.”
Jasmine Reed, a CDC spokeswoman, says most COVID-19 patients test positive at five days, and a ”fairly large” percentage test positive after 10 days. But she says infectiousness drops significantly at eight days, with few people remaining contagious at 10 days.
Chart by Nature Communications shows the probability of post-quarantine transmission and optimal day to conduct the test when an infected individual enters quarantine uniformly within the incubation or asymptomatic period, for no testing and three testing strategies, and durations of quarantine from 1 to 14 days, with an incubation period of 8.29 days, 30.8% asymptomatic infections and perfect self-isolation of symptomatic infections. Wells, C.R., Townsend, J.P., Pandey, A. et al. Optimal COVID-19 quarantine and testing strategies. Nat Commun 12, 356 (2021). https://doi.org/10.1038/s41467-020-20742-8
How can you tell if you are infectious or not after the five days of isolation?
The CDC recommends taking precautions and wearing a well-fitting mask until day 10. If there are no symptoms after five days, isolation is no longer necessary but mask-wearing should continue. No test can say for sure whether someone is contagious or not, though studies suggest that a positive result on rapid home antigen test can be indicative of infectiousness since these tests show positive when a person is carrying large amounts of the virus.
What about Long-COVID-19 patients?
A recent study out of China found that more than half of the COVID-19 patients discharged from a Wuhan hospital in 2020 still had at least one symptom two years later.
While the patients in the study did report some symptom improvement over time, most experienced poorer health than the general population. According to the U.S. CDC, some people who have recovered from COVID-19 can continue to test positive for the virus for up to three months, but those patients are not likely infectious.
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