Choir practice may have facilitated the quick transmission of Covid-19 to members of a church choir, most likely through close proximity of choir members during practices and the act of singing itself within such close quarters, according to a recently report published in Morbidity and Mortality Weekly Report.
“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,” wrote Lea Hamner, MPH, Skagit County Public Health, Mount Vernon, WA, and colleagues.
Through March 10, the 122-member choir met each week for a 2.5-hour practice. For the March 10 practice, chairs for the 61 members attending had been arranged in 6 rows of 20 chairs each that were spaced 6 to 10 inches apart with a center aisle.
By March 11 or 12, the choir director emailed the group warning that at least six members had developed a fever, and two had been tested for SARS-CoV-2 and were waiting for test results. By March 16, three members had tested positive for SARS-CoV-2, without indicating a common source of exposure. By March 17, the choir director informed the group that 24 members reported having developed flu-like symptoms since March 10, and that at least one tested positive for SARS-CoV-2. The two emails from the choir director caused many of the choir members to self-isolate/quarantine before Skagit Country Public Health (SCPH) was informed on March 17.
There was an initial investigation of the cluster on March 18-20, and all 122 members were interviewed either during this or a follow-up interview on April 7-10. Most participated in both interviews, in which choir practice attendance on March 3 and March 10 was established. Choir members were also asked about their attendance at other church events during March, other potential exposures, and symptoms of Covid-19. Even those without symptoms were instructed to quarantine for 14 days from their last choir practice.
In all, 78 choir members attended the March 3 practice, and 61 attended the March 10 practice. Subsequently, 86.7% (n=52) became ill. Among the 21 members who attended only the March 3 practice, only one became ill. Among three members who attended only the March 10 practice, two became ill, and one was laboratory-confirmed positive for Covid-19.
For a full 92.5% of patients, onset of illness began March 11 through 15. Median time to symptom onset was 10 days from the March 3 practice (range: 4-19 days), and three days from the March 10 practice (range: 1-12 days).
Odds of illness after the March 3 practice were 17.0 times higher for those who attended the practice compared with those who did not (95% CI: 5.5-52.8). After the March 10 practice, these odds were 125.7 times higher (95% CI: 31.7-498.9).
“The clustering of symptom onsets, odds of becoming ill according to practice attendance, and known presence of a symptomatic contagious case at the March 10 practice strongly suggest that date as the more likely point-source exposure event. Therefore, that practice was the focus of the rest of the investigation,” noted the authors. “Members had an intense and prolonged exposure, singing while sitting 6–10 inches from one another, possibly emitting aerosols,” they added.
The choir member who became ill on March 7 was identified as the index patient.
Among the 61 members in attendance at the March 10 practice, the median age was 69 years and 84% were women. The median age of those who became ill was 69 years, and 85% were women. In all, 86.7% of these choir members became ill (n=52), 61.5% were RT-PCR confirmed, and 38.5% were considered as having probable infection. Those in attendance at this practice developed symptoms a median of three days after the practice (range: 1-12 days).
The first SARS-CoV-2 test was performed on March 13, and the last on March 26. Three of the 53 patients were hospitalized (5.7%), and 3.8% (n=2) died. Mean time from onset of illness to hospitalization was 12 days. In the two patients who died, time from illness onset to death was 14 and 15 days, respectively.
The most commonly reported signs and symptoms at the time of illness onset and at any time during the course of illness among choir members with confirmed infection included cough (54.5% and 90.9%, respectively), fever (45.5% and 75.8%, respectively), myalgia (27.3% and 75.0%, respectively), and headache (21.2% and 60.6%, respectively).
Gastrointestinal symptoms developed in several patients, including diarrhea (18.8%), nausea (9.4%), and abdominal cramps/pain (6.3%). Only one person exhibited only loss of smell and taste.
The most severe complications included viral pneumonia in 18.2% and severe hypoxemic respiratory failure in 9.1%.
The most common risk factor for severe illness was age, with 75.5% of those who were aged ≥ 65 years infected. Most patients (67.7%) had no underlying medical conditions. Only a few (9.4%) had one underlying medical condition and 22.6% had two or more. All three patients who were hospitalized had two or more underlying medical conditions.
Fortunately, because of the speed of communications about the infections to members and timely notification to SCPH of a cluster of cases (on March 18), further spreading of Covid-19 was contained. All persons attending the March 10 practice had already begun self-isolation or quarantining by the time SCPH first contacted them March 18-20 as a result of two timely emails from the choir director informing them about the number of illnesses in members and proper social distancing and symptom awareness measures.
Limitations of this report include the non-reporting of the seating chart and the failure of 19 choir members with probable infection to seek confirmatory testing.
“Transmission was likely facilitated by close proximity (within 6 feet) during practice and augmented by the act of singing. 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,” concluded Hamner and fellow authors.
Almost 90% of choir members became infected with SARS-CoV-2 following a single choir practice.
This superspreader event highlights the importance of physical distancing in preventing transmission of SARS-CoV-2.
E.C. Meszaros, Contributing Writer, BreakingMED™
No conflicts of interest were reported by Hamner.
This report was funded through a Public Health Emergency Preparedness grant from the Washington State department of Health.
Cat ID: 125
Topic ID: 79,125,730,933,125,190,520,926,192,927,151,928