Chorale Investigation

This graphic from the Centers for Disease Control and Prevention shows how the coronavirus spread during a March practice of the Skagit Valley Chorale.

A cluster of COVID-19 cases in Skagit County is presenting a unique opportunity to study the illness, according to a report from Skagit County Public Health.

The report, prepared for the U.S. Centers for Disease Control and Prevention, details a cluster of cases in members of the Skagit Valley Chorale singing group that emerged in mid-March and led to 52 members developing symptoms.

Of the 61 members who attended the March 10 practice, 32 tested positive for the virus, and 20 had symptoms and were probably positive, according to the report. Three of the members were hospitalized, and two died.

While documented clusters of COVID-19 cases nationwide aren’t unique, few others have had a single documented point of exposure, and this presents a rare opportunity to better study how the virus spreads, according to the report.

Howard Leibrand, the county’s health officer, said the county’s report will be referred to globally, as researchers race to study the virus and governments mull reopening their economies.

“This article will be referenced hundreds of times in the next six months,” he said.

Lea Hamner, communicable disease and epidemiology lead for Public Health, said the average infected person spreads the virus to two or three others, much lower than the 52 infections documented in this case.

She said this shows how quickly the virus spreads, and is the reason for recommendations to stay home, wear face coverings and practice social distancing.

“Those recommendations are incredibly important in the wake of these findings,” she said.

The report indicates the nature of the meeting likely had some bearing on the spread of the virus.

“The 2.5-hour singing practice provided several opportunities for droplet ... transmission, including members sitting close to one another, sharing snacks, and stacking chairs at the end of the practice,” the report reads.

With members singing in close proximity to each other, the spread of saliva droplets that serve as a vector for infection was likely higher, the report states.

Leibrand said this incident doesn’t provide evidence that the virus can spread via aerosol — the suspension of fine solid particles or liquid droplets in air — but said the distinction is minimal considering small enough droplets essentially mimic the behavior of aerosol transmission.

The county had issued social distancing recommendations earlier on the day of the choir practice, but the information hadn’t reached members by practice that evening, the report states.

A member reached out to the county on March 17 to report that members had developed symptoms, and informed Public Health that many were already self-isolating or quarantining.

— Reporter Brandon Stone:, 360-416-2112, Twitter: @Brandon_SVH

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