The isolation period for people with Covid-19 may need to increase to 30 days to avoid the risk of secondary infection, a study has suggested.
Italian researchers followed over 4,500 Covid-positive patients in early coronavirus hotspot Reggio Emilia province, in the Emilia-Romagna region of Italy, between 26 February and 22 April.
Using regular swab testing, they found that the average time to viral clearance was 30 days after the first positive swab, and 36 days after the start of symptoms.
They further noted it took slightly longer in older patients and in those with more severe infection for the virus to clear.
They conclude that people with Covid-19 symptoms should be re-tested for the virus after four or more weeks to check whether they could still infect others.
However the did concede that previously published experimental research has indicated that a person is probably not infectious during convalescence even if they test positive.
The researchers said: ‘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 paper, published in BMJ Open, said: ‘Our data indicate that testing at 14 days from diagnosis, as many regional surveillance protocols recommend, will result in most cases still being positive. So that at least half of these tests are negative, testing should be done after more than four weeks once patients are symptom-free.
‘What’s more, given the high probability a priori of viral persistence, negative tests three weeks from diagnosis have a high probability of being false negatives.’
The paper concluded: ‘Postponing follow-up testing of clinically recovered Covid-19 patients could increase the efficiency and performance of testing protocols.
‘Understanding viral shedding duration also has implications for containment measures of paucisymptomatic subjects.’
In the UK, people are advised to self-isolate for just seven days after first experiencing Covid-19 symptoms.