Multiple reports have documented events involving superspreading of COVID-19; however, few have documented a community-based point-source exposure. This CDC report details a cluster of 52 secondary cases of COVID-19 following a 2.5 hour choir practice attended by 61 people, where 1 person was symptomatic.
Following the choir practice, there were 32 confirmed and 20 probable secondary COVID-19 cases (attack rate = 53.3% to 86.7%) stemming from the index case; in addition, 3 patients were hospitalized, and 2 died. The median interval from exposure during the March 10 practice to onset of illness was 3 days, which is shorter that the median incubation period of COVID-19 estimated from other studies. Transmission was likely facilitated by close proximity (within 6 feet) during practice and augmented by the act of singing.
The authors conclude that this outbreak of COVID-19 with a high secondary attack rate indicates that SARS-CoV-2 might be highly transmissible in certain settings, including group singing events. The findings underscore the importance of physical distancing, including maintaining at least 6 feet between persons, avoiding group gatherings and crowded places, and wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain. Enhancing community awareness can also encourage symptomatic persons and contacts of ill persons to isolate or self-quarantine to prevent ongoing transmission.