New Delhi: Patients suffering from Covid-19 are most infectious during their first week of illness, and therefore, it is important to isolate them early, researchers from the UK and Italy have said.
Shedding of the SARS-CoV-2 virus has been one of the areas of intense research from the start of the pandemic to understand the dynamics of the disease transmission in order to limit its spread.
“Although SARS-CoV-2 RNA shedding in respiratory and stool samples can be prolonged, duration of viable virus is relatively short-lived. SARS-CoV-2 titres in the upper respiratory tract peak in the first week of illness. Early case finding and isolation, and public education on the spectrum of illness and period of infectiousness are key to the effective containment of SARS-CoV-2,” researchers from the University of Edinburgh, University of St Andrews, and Cotugno Hospital in Naples reported in The Lancet Microbe journal Friday.
“This is the first systematic review and meta-analysis that has comprehensively examined and compared viral load and shedding for these three human coronaviruses. It provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more difficult to contain,” said lead author, Dr Muge Cevik, of the University of St Andrews, UK.
“Our findings are in line with contact tracing studies, which suggest the majority of viral transmission events occur very early, and especially within the first five days after symptom onset, indicating the importance of self-isolation immediately after symptoms start,” he added.
The researchers further said there’s a need to raise public awareness about the range of symptoms linked with the disease, including mild symptoms that may occur early on in the course of the infection than those that are more prominent like cough or fever.
Also read: Asymptomatic children with Covid can shed virus for weeks, finds South Korean study
Patients shed virus for upto 83 days
The meta-analysis, which looked at published research on viral shedding, came to the conclusion that Covid patients shed the virus for a very long time, but are infectious for only for a short period.
“Our findings suggest that, although patients with SARS-CoV-2 infection might have prolonged RNA shedding of up to 83 days in upper respiratory tract infection, no live virus was isolated from culture beyond day 9 of symptoms, despite persistently high viral RNA loads,” the researchers wrote.
“This finding is supported by several studies demonstrating an association between viral load and viability of virus, with no successful culture from samples below a certain viral load threshold. These findings indicate that, in clinical practice, repeat testing might not be indicated to deem patients no longer infectious. Duration of infectiousness and subsequent isolation timelines could reflect viral load dynamics and could be counted from symptom onset for 10 days in non-severe cases,” they added.
The viral load in the upper respiratory tract — which is a key indicator of how likely a person is to spread the virus when they cough, sneeze or talk loudly — peaked in the first week of symptom onset, the researchers said.
Later, it shifted to the lower respiratory tract. In stool samples though, the virus can be detected for upto three weeks though these are basically viral fragments and not the whole virus that can cause infection, they added.
Also read: Coronavirus patients shed virus even after their symptoms subside, says German study