The ban arose out of reports in the United States in March 2020 that 52 of 61 singers who attended a rehearsal of the Skagit Valley Chorale, in Mount Vernon, Washington, had subsequently contracted Covid. The source was judged to have been a chorister at the practice who later tested positive for the virus, and was considered the super-spreader.
The Los Angeles Times carried the headline: “A choir decided to go ahead with rehearsal. Now dozens of members have Covid-19 and two are dead.” An investigation by the county’s public-health officials was referred to in other scientific papers and widely disseminated, and, with a growing consensus that airborne droplets were spreading the virus, all indoor singing was banned (Comment, 4 June 2020).
It dealt a serious blow to many choirs, both professional and amateur (News, 29 May 2020, 19 June 2020, 26 May 2021). Scientific study accelerated. Two lay vicars from Salisbury Cathedral took part in rigorous trials at Porton Down, the MOD’s Science and Technology laboratory, to test how far airborne droplets could travel. These, and other studies commissioned by the Department for Digital, Media, Culture and Sport, were reported eventually to have given the Government confidence to reconsider appropriate mitigations.
Now a review of the Skagit case by scientists at Nottingham Trent University (NTU), Brunel University, and Brighton and Sussex Medical School, has concluded that many of the choristers’ symptoms had started too early to have been caused by the rehearsal.
In a paper entitled The Skagit County Choir COVID-19 Outbreak: Have we got it wrong? they review and analyse the original outbreak data in relation to published data on incubation. They conclude that it was “vanishingly unlikely that this was a single point source outbreak as has been widely claimed and on which modelling has been based”.
An unexamined assumption led to “erroneous policy conclusions about the risks of singing, and indoor spaces more generally, and the benefits of increased levels of ventilation”, the paper says.
“Although never publicly identified, one individual bears a moral burden of knowing what health outcomes have been attributed to their actions. We call for these claims to be re-examined and for greater ethical responsibility in the assumption of a point source in outbreak investigations.”
A graph from the report showing that the outbreak largely pre-dated the expected pattern (the curve) had there been a super-spreader at the rehearsal
One of the co-authors, Professor Robert Dingwall, of NTU, said on Wednesday that the speed with which the choristers were being infected and displaying symptoms was implausible, and did not fit the epidemic curve.
“All the ‘mights’ got turned into definite findings by the people who quoted [the original study],” he said. “We looked at it and saw the distribution of days on which the symptoms appeared, and realised they just couldn’t all have been affected at that rehearsal — the symptoms were just appearing too quickly.”
The research established that there were several people present who had been infected earlier, and two were incubating symptoms. “It’s wrong to say that this was uniquely dangerous,” Professor Dingwall said. “We looked up the church on Google Maps to see the layout. . . You would have to be there for something like 44 hours before there was any question of re-breathing anyone else’s air.”
The paper concludes that the epidemic curve was not consistent with a single source. It emphasises that it is not a criticism of the original outbreak investigation, which, it says, “was clearly carried out in a professional manner and with appropriate restraint in its conclusions, given the state of knowledge at the time”.
The space that the 61 singers used that night would easily have accommodated the full complement of 120. It was a church space, with a vaulted ceiling, doors opening and constant air movement; so it did not make sense to imagine that there were clouds of fine droplets drifting around and being inhaled. There was solid evidence, too, the researchers suggest, that in normal circumstances, breath typically travelled only 20cm.
The researchers conclude: “To the extent that this outbreak report has been misused as a template, it is likely that other events have been wrongly characterised as single source, that there has been a misconceived search for super-spreaders, and a rush to excessive investments in ventilation technologies for enclosed spaces based on models that have assumed what their author should have questioned.
“There is also a more general question about the extent to which the literature contains taken for granted papers that have not been subject to critical re-examination.”