People who have had coronavirus should be tested again four weeks later says study
The researchers who operated in one of Italy’s former coronavirus hotspots, say this is because SARS-CoV-2, the virus responsible for Covid-19 infection, 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.
And it’s not yet known how infectious a person may be in the recovery phase, warn the scientists.
What’s more, the findings indicate that the rate of false negative test results--whereby people are falsely reassured they no longer have active (shedding) virus in their bodies--is relatively high (1 in 5) in early convalescence, so putting them at risk of unwittingly passing on the infection.
An accurate assessment of how long it takes the body to clear SARS-CoV-2 is key to curbing the risk of onward infection and minimising the enforced isolation period for patients who no longer have symptoms, say the researchers.
They tracked the progress of 4538 residents of the Reggio Emilia province , all of whom tested positive for the virus between February 26 and April 22 this year.
Italy was the first Western country to be badly affected by Covid-19.
Because of missing data, 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 time to viral clearance was 31 days from the first positive swab test.
Based on their findings, the researchers suggest retesting 14 days after a positive swab will, in most cases produce the same result, and there’s still a relatively high rate of false negative results when retesting up to 3 weeks later.
They point out experimental research indicates that during convalescence a person is probably not infectious, even if they test positive, prompting the WHO to recommend a period of up to 13 days of isolation for those with symptoms and 10 days for those without.