Asymptomatic Transmission During the Coronavirus Disease 2019 Pandemic and Implications for Public Health Strategies

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread rapidly in a few months despite global public health strategies to curb transmission by testing symptomatic patients and social distancing. This review summarizes evidence that highlights transmission by asymptomatic and presymptomatic individuals. Viral load of asymptomatic and symptomatic cases is comparable. Viral shedding is highest before symptom onset, suggesting high transmissibility before symptoms. Within universally tested subgroups, high percentages of SARS-CoV-2 infected asymptomatic individuals were found. Asymptomatic transmission was reported in several clusters, including a Wuhan study showing an alarming rate of intrahospital transmission. Several countries reported higher prevalence among healthcare workers than general population raising concern that healthcare workers could act as silent vectors. Therefore, current strategies that rely solely on "symptom onset" for infection identification need urgent reassessment. Extensive universal testing irrespective of symptoms may be considered, with priority placed on groups with high frequency exposure to positive patients.