A CDC investigation revealed that over a single 2.5-hour choir practice, a single symptomatic person infected up to 86.7% of the people in the choir.

In mid-March, a member of a choir in Skagit County, Washington informed the public health council that several of the 122 choir members had become ill. Three of them had already positive tests for SARS-CoV-2, and another 25 people had symptoms.

The choir met for a 2.5-hour practice every Tuesday evening through March 10, with 61 members attending the March 10 session. A single symptomatic person was present at that session.

In total, 53 cases were confirmed, and another 20 developed symptoms without being tested for COVID-19. Out of the total cases, 3 people were hospitalized, and 2 did not survive.

This case highlights just how much the disease can spread, even from a single case, if the environment is favorable for the virus.

The choir members sat close to each other, shared snacks, and arranged the chairs at the beginning and the end. The act of singing itself might have contributed to the transmission through the emission of aerosols.

This demonstrates the high transmissibility of SARS-CoV-2 and the possibility of super-emitters that contribute to broad transmission in certain circumstances. The potential for superspreader events underscores the importance of physical distancing, including avoiding gathering in large groups, to control spread of COVID-19. The CDC writes that this underlines the importance of maintaining distancing:

“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. This underscores 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 during this pandemic.”

Here’s the very unfortunate part, however: all this could have been avoided. The choir respected the guidance that was in place at the time. Now, the guidance recommends that face-to-face contact is avoided, but at the time, it was within guidance.

It is recommended that persons avoid face-to-face contact with others, not gather in groups, avoid crowded places, maintain physical distancing of at least 6 feet to reduce transmission, and wear cloth face coverings in public settings where other social distancing measures are difficult to maintain.

Although the epidemic was in full force in Europe at the time, most places in the US delayed strict guidance. The problem was further exacerbated by the fact that among the 61 choir members who attended the March 10 practice, the median age was 69 years.

Current CDC recommendations, including maintaining physical distancing of at least 6 feet and wearing cloth face coverings if this is not feasible, washing hands often, covering coughs and sneezes, staying home when ill, and frequently cleaning and disinfecting high-touch surfaces remain critical to reducing transmission. Additional information is available at CDC’s page.