A surprising way you may risk getting Covid-19

Much of what we understand about the transmission of infectious diseases is derived from odd outbreaks in far-flung places. For example, we learned more about measles from its rapid spread on an isolated Polynesian island in 1911 and about influenza from people stuck on a grounded plane in Alaska in 1979.

Add to this important list a startling and revealing outbreak of Covid-19 affecting as many as 52 of 61 people at a choir practice in March. The story was detailed this week in a new report from the US Centers for Disease Control and Prevention.

Public health officials in Skagit County, Washington, which lies between Seattle and the Canadian border, meticulously reconstructed the outbreak. The area had already seen a nursing home outbreak in nearby Kirkland, and testing and local expertise were therefore available.

After interviewing everyone involved in the March 10 choir practice, and determining precisely how the chairs been arranged and where each choir member had been sitting, standing and later mingling, the investigators determined that one person with mild respiratory symptoms (and who later tested positive for Covid-19) had likely triggered the outbreak.

They found that, at the start of the practice, all 61 members sang together in a room for 40 minutes. Then they split into two groups in two rooms for an additional 50 minutes. Next came a 15-minute break, where the whole group chatted and snacked on cookies and oranges.

Finally, the large group returned to their seats in the main room and practiced for another 45 minutes before re-stacking their chairs and leaving.

Within the next five days, 49 people developed symptoms of Covid-19. The early development of symptoms was remarkable (at a median of 3 days versus 5 days in most other reports) and may relate to the intensity of the exposure. Three additional cases developed symptoms over the next week.

The choir members were almost all women (84%) with an average age of 69 years. Of those with symptoms, 32 tested positive for Covid-19. Another 20 were not tested but were considered probable cases based on symptoms and association with the lab-proven cases. Three of the 52 were hospitalized, including two who died from the infection about two weeks after developing symptoms. As with other reports, the three hospitalized patients had at least two pre-existing health conditions.

According to the report, the choir members risked infection when moving and stacking the chairs, sharing snacks and touching common areas.

But the most likely way the virus spread was through singing and chatting while sitting close together.

The possibility that singing might help transmit infectious diseases is not a new concept. A 1968 article, “Singing and the Dissemination of Tuberculosis,” described an elaborate box that volunteers could talk, sing and cough into, allowing investigators to measure the number, size and length of time airborne of individual infectious droplets they breathed out. And a few TB outbreaks have featured singing, including one in a New Jersey church choir in 1995.

The public health implications of this report are considerable. First, additional respect emerges for the highly contagious nature of Covid-19, with so many exposed persons being infected after a single, intensive exposure. Second, despite the older age of those infected, hospitalization was rare probably because of the overall good health of the group.

The outbreak also provides strong if indirect support for continued adherence to current CDC guidelines that emphasize physical distancing as well as active screening with self-isolation of those with even mild symptoms. Until we have capacity for accurate testing with rapid results, we will be left with this sturdy, grandmotherly advice that saw countless generations in the pre-vaccine era through countless other epidemics.

The report of this outbreak also includes an important limitation. The authors decided not to map out where each of the 32 confirmed, 20 probable and 8 uninfected persons sat, though they had constructed a complete seating chart. This weakened the article a small amount, but the decision was made to protect patient privacy, an extremely important but sometimes overlooked aspect of any outbreak investigation.

Indeed, the relentless pursuit and exposure of a culpable so-called “patient zero” is not only of little value in an epidemiological context. It’s also vindictive and potentially life-altering for anyone correctly — or, worse, incorrectly — identified as the putative “source” of the misery for so many in the community. As with other aspects of this complex epidemic, the maintenance of our humanity first and foremost must remain the everyone’s highest priority.