A report published online by the Centers for Disease Control and Prevention on Friday found that one symptomatic coronavirus patient infected 86.7 percent of the 60 attendees at a 2.5-hour choir practice.
- On March 17, a member of a choir in Skagit County, Washington, reported to Skagit County Public Health that several people in the 122-member choir had become ill, with three testing positive for COVID-19 and another 25 showing related symptoms.
- SCPH found that after a choir practice on March 10 attended by one symptomatic person, 53 coronavirus cases were identified, where 33 were confirmed and 20 were probable.
- The practice had an 86.7 percent overall infection rate and a 5.7 percent hospitalization rate as three members were taken to the hospital. Two people died, resulting in a 3.7 percent death rate.
- SCPH observed that the virus was transmitted through the air and touching contaminated surfaces, as choir members sat close to each other, sang together, shared snacks and stacked chairs at the end of practice.
- The March 10 practice attendees were instructed by SCPH via telephone, email and post mail to self-isolate. Contact tracing was used to identify others exposed to the patients, who were then directed to quarantine.
- Before the choir outbreak, Skagit County only had seven confirmed COVID-19 cases.
The CDC warned in its report that:
The potential for superspreader events underscores the importance of physical distancing, including avoiding gathering in large groups, to control spread of COVID-19. Enhancing community awareness can encourage symptomatic persons and contacts of ill persons to isolate or self-quarantine to prevent ongoing transmission.