High SARS-CoV-2 attack rates following exposure during singing events in the Netherlands, September-October 2020

Shah, A. A.; Dusseldorp, F.; Veldhuijzen, I. K.; te Wierik, M. J. M.; Bartels, A.; Schijven, J.; Vermeulen, L. C.; Knol, M. J.

Previous reports indicate that there may be an increased risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission during singing events. We describe SARS-CoV-2 transmission in six singing events from September-October 2020, across the Netherlands, with attack rates from 25-74%. We investigated potential routes of SARS-CoV-2 transmission for each event. Events included 9-21 persons, aged 20-79 years. SARS-CoV-2 transmission likely took place during five out of six events; a possible index case could be identified in four out of five clusters. Limited sequencing data was available, hampering interpretation of results. Indirect contact and droplet transmission (<1.5m) may have caused some cases, but are unlikely to explain the high attack rates. The previously published AirCoV2 model indicated that airborne transmission (via infectious droplets/ aerosols over longer distances (>1.5m)) due to singing is possible in case of supershedder presence ([≥]1010 RNA copies/mL). Also, airflow expelling respiratory droplets over longer distances (>1.5m) may have influenced transmission. In conclusion, a combination of transmission routes probably caused these five clusters. Proportions attributable to each route cannot be deduced. It is possible that airborne transmission of SARS-CoV-2 due to singing (partly) led to the high attack rates observed in these clusters.