High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice - Skagit County, Washington, March 2020

Area of Science:

• Epidemiology
• Infectious Disease Transmission
• Public Health

Background:

• A cluster of SARS-CoV-2 infections was identified following a choir practice in Skagit County, Washington.
• Several choir members reported illness, with initial cases testing positive for SARS-CoV-2, the virus causing COVID-19.

Purpose of the Study:

• To investigate the transmission dynamics of SARS-CoV-2 within a choir group.
• To assess the secondary attack rate and identify risk factors associated with the observed COVID-19 outbreak.

Main Methods:

• Public health officials investigated the outbreak by obtaining a choir member list and identifying symptomatic individuals.
• Case definitions for confirmed and probable COVID-19 cases were applied to attendees of a specific choir practice.
• Transmission rates were calculated based on the number of attendees and identified cases.

Main Results:

• Out of 61 attendees at a March 10 practice, 53 cases of COVID-19 were identified (33 confirmed, 20 probable), resulting in a high secondary attack rate.
• Hospitalization occurred in 5.7% of ill individuals, and 3.7% died.
• The 2.5-hour practice involved close proximity, shared items, and singing, creating opportunities for droplet, fomite, and aerosol transmission.

Conclusions:

• The study demonstrates the high transmissibility of SARS-CoV-2, particularly in group settings involving singing.
• Superemitters may play a role in amplifying transmission during such events.
• Recommendations include avoiding gatherings, maintaining physical distancing, and wearing face coverings to mitigate SARS-CoV-2 spread.