According to a population study based in Italy, people who have had COVID-19 should be retested 4 or more weeks after symptoms appear for the first time. This is because 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.
However, the percentage of how infectious a person may be in the recovery phase is not yet known. The findings indicate that the rate of false-negative test results is relatively high (1 in 5) in early convalescence. This puts people at risk of unwittingly infecting others. An accurate assessment of how long it takes the body to clear SARS-CoV-2 is the key to curbing the risk of onward infection.
Around 4480 people were included in the preliminary analysis; 1259 achieved viral clearance, determined by at least one negative swab test after the initial positive test, and 428 died. The average viral clearance time taken was 31 days post the positive test. To understand the speeds of viral clearance, 1162 people out of the original 4480 were retested an average of three times: around 15 days post the first positive swab; 14 days post the second, and 9 days post the third. Viral clearance was detected in 704 and confirmed in just fewer than 79% of those tested again after the first negative swab. The average time taken by a patient to viral clearance in this group was 30 days after the first positive swab and 36 days after the start of symptoms but took a little longer depending on age and severity of the infection.
Based on their findings, researchers suggested that to avoid generating secondary cases, either the isolation period should be longer i.e. 30 days from the start of symptoms or at least one follow-up test should be done before ceasing isolation.