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A study published yesterday in The Lancet microbe shows that COVID-19 is most contagious within the first 5 days of symptom onset, highlighting the importance of early case identification and quarantine.
Led by researchers at the University of St. Andrews in Scotland, the systematic review and meta-analysis included 98 studies of 7,997 patients infected with coronaviruses that cause COVID-19 (SARS-CoV-2), acute respiratory syndrome severe (SARS-CoV -1) or Middle East respiratory syndrome (MERS-CoV). Seventy-nine of the studies (81%) involved patients with COVID-19.
The duration of viral RNA shedding was on average 17 days in the upper respiratory tract, 14.6 days in the lower respiratory tract, 17.2 days in the stool and 16.6 days in the serum. The longest shedding periods were 83 days in the upper respiratory tract, 59 in the lower respiratory tract, 35 days in the stool and 60 days in the serum.
Eight studies that used respiratory samples from patients during their first week of illness were successful in growing the virus live, but no live virus was found in any sample taken 9 days after symptom onset, despite persistent high viral loads.
The viral load of SARS-CoV-2 peaked in the upper respiratory tract, believed to be the main source of transmission, within the first 5 days of onset of symptoms. SARS-CoV-1 peaked between 10 and 14 days and MERS-CoV peaked between 7 and 10 days, which researchers believe could explain why COVID-19 is spreading faster in the community and is more difficult to contain.
Infectious for about 9 days
The study found no difference between peaks in viral load in patients with COVID-19 with and without symptoms, but the indications are that asymptomatic patients clear the virus more quickly and therefore could be contagious for a longer period. short.
Although the authors said they could not recommend an optimal quarantine time because their study looked only at confirmed cases rather than possible exposures, the results seem to indicate that people with COVID-19 may infect other people for about 9 days. Most countries currently recommend that patients with COVID-19 be quarantined for 10 days.
But the researchers warn that many patients in the studies they analyzed were hospitalized and received different therapies that may have changed the course of their infection and therefore their period of infectivity.
“In addition, the growing deployment of treatments, such as dexamethasone, remdesivir as well as other antivirals and immunomodulators in clinical trials, is likely to influence viral shedding in hospitalized patients,” co-author Antonia Ho , PhD, MBChB, MRes, of MRC-University of Glasgow Center for Virus Research, said in a press release from The Lancet. “Further studies on viral shedding in this context are needed.”
Immediate quarantine, contact tracing
Understanding the contagious pattern of COVID-19 is important for public health officials who are developing measures to control its transmission, the researchers said.
“Our results are consistent with contact tracing studies which suggest that the majority of viral transmission events occur very early, and particularly within the first 5 days after symptom onset, indicating the importance of self – isolation immediately after onset of symptoms, ”senior author Muge Cevik, MD, MSc, of the University of St. Andrews, said. “We also need to educate the public about the range of symptoms related to the disease, including mild symptoms that may occur earlier in the infection than larger ones like cough or fever.”
Cevik also said repeat diagnostic testing for COVID-19 may not be necessary to decide whether a patient is no longer contagious, “because that could stay positive for much longer and does not necessarily indicate that he could transmit the virus to others.In patients with non-severe symptoms, their period of infectivity could instead be counted as 10 days from the onset of symptoms.
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