A single person in the US infected 52 other people with Covid-19 – two of whom later died – after meeting for a church choir practice, according to a new report by the US Centers for Disease Control and Prevention (CDC).
The case study shows how relentlessly Covid-19 can spread throughout a group, especially among older populations, due to a single “superspreader”. However, it also demonstrates the power of tracking cases and self-quarantining; the outbreak was largely contained from the wider community thanks to the choir members swiftly isolating themselves after they became infected.
The outbreak began on the evening of March 10, 2020, when a large group met for choir practice at a church in Skagit County, Washington State. The virus was already killing people in the Seattle area, so there was a reluctance to meet up for that week’s practice, according to the Los Angeles Times, who reported on the outbreak in March before the CDC'S report.
Despite some unease, 61 of the usual 122 choir members showed up and the practice went ahead. Due to the rising concern of Covid-19, members did not greet each other with hugs and handshakes, while hand sanitizer was offered to people as they entered the building.
Over the course of the 2.5-hour practice, the group sang together in a large multipurpose room – seats had been separated but were still just 15-25 centimeters (6-10 inches) apart – before splitting into two smaller groups for a further 50-minute singalong. They also had a 15-minute break, in which cookies and oranges were laid out to eat, although many did not partake. When the practice finished, each member returned their chair, causing a congregation around the chair racks, before parting ways.
According to the report, which interviewed all 122 members of the choir, only one person who attended that night had reported feeling sick with cold-like symptoms for at least three days. They later tested positive for Covid-19. As such, this is being documented as a “superspreading event” because all infections appear to have emerged from this single infected person.
Between March 11-15, a number of other choir members started to experience coughs and fever. Eventually, 52 (86.7 percent) others of the 60 attendees became infected with Covid-19. Three of the total 53 patients were hospitalized, two of whom died. The choir members ranged in age from 31 to 83, but the median age was 69 years, meaning many of them are considered “at higher risk” according to CDC guidelines. A member of the choir contacted the local health authorities to notify them, while the choir director emailed the members, leading many to self-isolate or quarantine.
The route of transmission is not clear. Although there were multiple opportunities for surface-to-surface transmission, the report speculates that the virus most likely spread by aerosolized transmission through the act of singing and loudly vocalizing thrusting a mist of virus-loaded droplets into the surrounding air.
There is some hope in this story, however. Within days of the meeting, all members of the choir were traced and contacted by health authorities, who issued them with self-isolation guidelines. While the report did not explicitly look to see how these measures prevented further outbreaks, local health authorities believe the choir members' prompt actions saved a lot of people from the infection.
“If they hadn’t initiated their own isolation and quarantine before we got involved, you can conceive of a situation where every one of those people would have infected another three people each,” Dr Howard Leibrand, the Skagit County health officer, told the New York Times. "You would have had a huge change in our viral curve based on this one episode.”