Milia-Romagna, Italy—
Even patients who appear to have recovered from COVID-19 might not have cleared the virus from their bodies after several weeks, according to a new study.

A report in BMJ Open explains that SARS-CoV-2 takes an average of 30 days to clear from the body after the first positive test result and an average of 36 days after symptoms first appear. Furthermore, according to the article, is still is not known how infectious patients are in the recovery phase.

Azienda USL-IRCCS di Reggio Emilia–led researchers caution that those who have had COVID-19 should be swab tested again 4 or more weeks after symptoms first appear. Their large population-based study conducted in one of Italy’s former coronavirus hotspots suggests that will minimize the risk of spreading infection.

Also an issue, according to the authors, is that a relatively high rate of false negative tests results—one in five—in early convalescence increase the risk of infecting others.

To try to develop an accurate assessment of how long it takes the body to clear SARS-CoV-2, researchers tracked 4,538 residents of the Reggio Emilia province in the Emilia-Romagna region of Italy, all of whom tested positive for the virus between February 26 and April 22, 2020.

Emilia-Romagna was one of the country's three coronavirus regional hotspots.

Because of missing data, 4,480 people were included in the preliminary analysis; 1,259 achieved viral clearance, as determined by at least one negative swab test after the initial positive test, and 428 died. The average time to viral clearance was 31 days from the first positive swab test.

Researchers then focused on the speed of viral clearance in 1,162 people out of the original 4,480 for whom sufficient time had passed since the first positive swab—at least 30 days. They retested each surviving patient an average of three times: around 15 days after the first positive swab; 14 days after the second; and 9 days after the third.

The authors report that viral clearance was detected in 704 (60.5%) and confirmed in slightly less than 79% of those tested again after the first negative swab (436/554). They assumed a rate of one false negative out of every five negative test results.

Results indicate that the average time to viral clearance in this group was 30 days after the first positive swab and 36 days after the start of symptoms, but it took longer in some cases depending on age and severity of the infection.

“To avoid generating secondary cases, either the isolation period should be longer (30 days from the start of symptoms) or at least one follow-up test should be done before ceasing isolation,” the researchers advise.

The World Health Organization recommends 13 days of isolation for those with symptoms and 10 days for those without, based on previously published experimental research indicating that, during convalescence, a patient is probably not infectious, even if they test positive.

“But the evidence on the risk of transmission during the convalescent phase characterized by a positive [swab test] is weak, and current serological data have not provided any additional insight. Furthermore, current epidemiological evidence of transmission has been influenced by how quarantine has been managed thus far,” the researchers for this study caution.

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