A study published yesterday in The Lancet Microbe shows that COVID-19 is most contagious in the first 5 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 (SARS-CoV-2), 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.

 

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