A choir practice that took place in early March in Skagit County, Washington turned out to be a super-spreading event in which 45 out of 60 people became infected with the coronavirus. No one was showing symptoms at the time, and no one hugged or shook hands, but they did spend two and a half hours in an enclosed space singing.

The Skagit Valley Chorale practice took place on March 10, and in the ensuing days, 75 percent of the choir members present that evening have fallen ill, with three hospitalized and two already dead. As the Los Angeles Times reports, this cluster of cases has epidemiologists concerned that six feet of distance is not sufficient, and that the accepted wisdom that the virus is spread primarily through droplets from coughs and sneezes is, at the very least, an incomplete picture of how this highly infectious virus spreads.

Members of the choir were already aware of the COVID-19 outbreak in their state, particularly around the Seattle area, which is about an hour south of Skagit County by car. Hand sanitizer was dispensed at the door of the practice that night in March, no one shared sheet music, and people were conscious not to stand too close to one another or engage in their huggy greetings. Also, no one remembers anyone coughing or sneezing, and no one present felt ill at the time. Nonetheless, a huge percentage of people present later tested positive for the virus.

While the World Health Organization has downplayed the role that the aerosolized droplets play in the spread of COVID-19, scientists have continued to explore the possibility of the airborne spread of this coronavirus. A small-scale study published on March 17 in the New England Journal of Medicine — which was cited in a Reddit AMA with two Boston ER doctors two weeks ago — suggests that live, viable virus can hang in the air for up to three hours.

And the Skagit County outbreak suggests that just singing — and forcefully expressing breath — might be enough to transmit virus into the air and spread it widely around you, even if you are not showing symptoms. Experts have previously warned that individuals are likely contagious for several days before showing symptoms, and some percentage of those infected never show symptoms at all.

The case brings echoes of the recent cruise ship outbreaks, as well as outbreaks in New Rochelle — which involved synagogue services with singing, and likely hugging — and a church in South Korea.

Linsey Marr, a researcher at Virginia Tech who's an expert in the airborne transmission of viruses, tells the LA Times that this outbreak should be a wakeup call for those who feel that social distancing measures are overblown. She cites the case of a 1977 Alaska Airlines flight in which three quarters of the passengers later came down with the flu — the plane was trapped on the tarmac in Homer, Alaska for four hours with engine trouble, with the ventilation system turned off, and one woman on the flight who was not yet symptomatic later fell ill. The case helped inform epidemiologists about how influenza can be spread through the air in an enclosed space.

Marr also tells the LA Times that certain people simply have "super-spreader" abilities in their lungs — capable of exhaling 1,000 times more fine material than most people.

While this case, which remains under investigation, should not scare people into hoarding N95 masks that will be key to saving healthcare workers from infection, it should give people pause about entering any enclosed space with strangers, whether they're coughing or not.

And, as the Boston doctors and others have suggested, homemade masks and standard surgical masks will provide some protection, especially for those at high risk who are nervous about being in public. The Chinese Center for Disease Control and the Czech Republic's health officials have both advocated for everyone wearing masks of some kind in public. And last week, the New York Times acknowledged that some health experts are coming around to the recommendation as well, especially for frontline workers who continue to ride public transportation.

Update: According to the Washington Post, the CDC is considering issuing a new advisory to the general public about wearing non-medical masks when in public spaces, however officials continue to say that this is to prevent the asymptomatic from spreading the virus, and that such masks do not protect the wearer from being infected.

Previously: Don't Hoard N95 Masks, But Surgical and Homemade Masks May Help If Your Roommate Is Coughing