FRIDAY, April 3, 2020 (HealthDay News) -- Presymptomatic transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been observed in epidemiological clusters in Singapore, with transmission occurring one to three days before symptom onset, according to research published in the April 1 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.
Wycliffe E. Wei, M.P.H., from the Ministry of Health in Singapore, and colleagues reviewed clinical and epidemiological findings of all COVID-19 cases in Singapore through March 16 to examine whether presymptomatic transmission had occurred.
The researchers identified seven COVID-19 epidemiologic clusters in which presymptomatic transmission likely occurred; within these clusters, 10 cases of presymptomatic transmission accounted for 6.4 percent of the 157 locally acquired cases. Presymptomatic transmission occurred one to three days before symptom onset in the presymptomatic source patient in the four clusters for which the date of exposure could be determined. Officials developing contact tracing protocols should strongly consider including a period before symptom onset to account for the possibility of presymptomatic transmission.
"The possibility of presymptomatic transmission of SARS-CoV-2 increases the challenges of COVID-19 containment measures, which are predicated on early detection and isolation of symptomatic persons," the authors write. "These findings underscore the importance of social distancing in the public health response to the COVID-19 pandemic, including the avoidance of congregate settings."