THURSDAY, Sept. 3, 2020 (HealthDay News) -- You tested positive for COVID-19 and dutifully quarantined yourself for two weeks to avoid infecting others. Now, you're feeling better and you think you pose no risk to friends or family, right?
Not necessarily, claims a new study that shows it takes roughly a month to completely clear the coronavirus from your body. To be safe, COVID-19 patients should be retested after four weeks or more to be certain the virus isn't still active, Italian researchers say.
Whether you are still infectious during the month after you are diagnosed is a roll of the dice: The test used in the study, an RT-PCR nasal swab, had a 20% false-negative rate. That means one in five results that are negative for COVID-19 are wrong and patients can still sicken others.
"The timing of retesting people with COVID-19 in isolation is relevant for the identification of the best protocol of follow-up," said lead researcher Dr. Francesco Venturelli, from the epidemiology unit at Azienda Unita Sanitaria Locale--IRCCS in di Reggio Emilia.
"Nevertheless, the results of this study clearly highlight the importance of producing evidence on the duration of SARS-CoV-2 infectivity to avoid unnecessary isolation without increasing the risk of viral spread from clinically recovered people," he added.
For the study, the researchers tracked nearly 4,500 people who had COVID-19 between Feb. 26 and April 22, 2020, in the Reggio Emilia province in Italy.
Among these patients, nearly 1,260 cleared the virus and more than 400 died. It took an average of 31 days for someone to clear the virus after the first positive test.
Each patient was tested an average of three times: 15 days after the first positive test; 14 days after the second; and nine days after the third.
The investigators found that about 61% of the patients cleared the virus. But there was a false-negative rate of slightly under one-quarter of the tests.
The average time to clearance was 30 days after the first positive test and 36 days after symptoms began. With increasing age and severity of the infection, it took slightly longer to clear the infection, the researchers noted.
"In countries in which the testing strategy for the follow-up of people with COVID-19 requires at least one negative test to end isolation, this evidence supports the assessment of the most efficient and safe retesting timing -- namely 30 days after disease onset," Venturelli said.
The report was published online Sept. 3 in the BMJ Open.
Dr. Marc Siegel, a professor of medicine at NYU Langone Medical Center in New York City, agreed that retesting is needed to be sure that the virus is no longer present.
"The advice to patients is to get tested again a month after your initial test," he said. "What's new here is the finding that the speed of viral clearance doesn't happen in a day, but in 30 days."
Siegel said that when a blood test for COVID-19 is perfected, it would be the best option to use to reduce the possibility of false-negative results.
The one caveat to retesting, he said, is that it shouldn't take tests away from people who need one to diagnose COVID-19. With tests still in short supply, massive retesting may have to wait until new antigen tests are widely available, he noted.
For more on COVID-19, head to the U.S. Centers for Disease Control and Prevention.
SOURCES: Francesco Venturelli, MD, epidemiology unit, Azienda Unita Sanitaria Locale--IRCCS di Reggio Emilia, Italy; Marc Siegel, MD, professor, medicine, NYU Langone Medical Center, New York City; BMJ Open, Sept. 3, 2020, online