Sept 16, 2020
Reviewed by Kelly Cawcutt, M.D., MS
The COVID-19 pandemic has brought unprecedented attention to contract tracing and risk factors for increased viral transmission, specifically of SARS-CoV-2. More epidemiologic research, like the large study from Luo et al. recently published in Annals of Internal Medicine, is critical to increasing our understanding in these areas.
In this study of 3,410 close contacts of persons infected with COVID-19 in China, only 127 (3.7%) of these contacts were secondarily infected. Settings where the contacts were exposed were divided into several categories: households, public transportation, health care settings, entertainment venues or workplaces, and multiple settings (indicating exposure in more than one contact setting). Of note, among those secondarily infected, only 8 (6.3%) were asymptomatic. Further analysis found that households had the highest rate of transmission (10.3%), including compared to health care settings (1.0%). Rates of secondary attack were also higher with more severe index case exposures and expectoration.
Key takeaways from the study are that risks for secondary transmission were highest among those in shared households and those exposed to sicker index cases. This further strengthens the fact that public transmission of SARS-CoV-2, among mask wearers, is not the primary driver of secondary infections.