(MENAFN – The Peninsula) QNA Edinburgh: A new study shows that COVID-19 is most contagious in the first five days after symptom onset, underscoring 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 on 7,997 patients infected with coronaviruses that cause COVID-19, severe acute respiratory syndrome (SARS-CoV-1), or Middle East respiratory syndrome (MERS-CoV). Seventy-nine of the studies (81%) involved COVID-19 patients.
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 stool, and 16.6 days in serum. The longest times of shedding were 83 days in the upper respiratory tract, 59 in the lower respiratory tract, 35 days in stool, and 60 days in serum.
Eight studies that used respiratory samples from patients in their first week of illness successfully cultured live virus, but no live virus was found in any sample collected after 9 days after symptom onset, despite persistent high viral loads.
SARS-CoV-2 viral load peaked in the upper respiratory tract, believed to be the primary source of transmission, in the first 5 days after symptom onset. SARS-CoV-1 peaked at 10 to 14 days, and MERS-CoV peaked at 7 to 10 days, which the researchers said may be why COVID-19 spreads more quickly in the community and is more difficult to contain.
The study found no difference between viral load peaks in COVID-19 patients with and without symptoms, but indications are that asymptomatic patients clear the virus faster and therefore could be contagious for a shorter time
While the authors said that they can’t recommend an optimal duration for quarantine because their study involved only confirmed cases rather than possible exposures, the results appear to indicate that people with COVID-19 can infect others for about 9 days. Most countries currently recommend that COVID-19 patients quarantine for 10 days.
But the researchers caution that many patients in the studies they analyzed were hospitalized and received different therapies that may have altered the course of their infection and therefore their period of infectiousness.
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