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

Background Previous reports suggest SARS-CoV-2 transmission risk increases during singing events. From September-October 2020, several clusters of COVID-19 cases among singing events were reported across the Netherlands. Our aim was to investigate whether singing increased SARS-CoV-2 transmission risk during these events. Methods Data from 5 events were retrospectively collected from spokespersons and singing group members via questionnaires. Information was consolidated with the National Notifiable Diseases Surveillance System. Specimens were requested for sequencing for point source and cluster assessment. We described outbreaks in terms of person, place and time and depicted potential SARS-CoV-2 transmission routes. A previously published model (AirCoV2) was used to estimate mean illness risk of 1 person through airborne transmission under various scenarios. Results Events included 9-21 persons (mean: 16), aged 20-89 years (median: 62). Response rates ranged 58-100%. Attack rates were 53-74%. Limited sequencing data was obtained from 2 events. Events lasted 60-150 minutes (singing: 20-120). Rooms ranged 320-3000m3. SARS-CoV-2 transmission likely occurred during all events; with a possible index case identified in 4 events. AirCoV2 showed 86% (54-100%) mean illness risk for 120 minutes of singing, smaller room (300m3), 1 air exchange/hour (ACH), and supershedder presence. Conclusions Droplet transmission and indirect contact probably caused some cases, but unlikely explain the high attack rates. AirCoV2 indicated that airborne transmission due to singing is possible in case of supershedder presence. Airflow expelling respiratory droplets >1.5m possibly influenced transmission. It is possible that singing itself increased SARS-CoV-2 transmission risk through airborne transmission. Summary This outbreak investigation among five singing events with high SARS-CoV-2 attack rates (53-74%) suggested that airflow expelling respiratory droplets >1.5m possibly influenced transmission and it is possible that singing itself increased SARS-CoV-2 transmission risk through airborne transmission. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement No external funding was received. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Centre for Clinical Expertise (KEC) at the RIVM assessed the study and verified whether the work complies with the specific conditions as stated in the law for medical research involving human subjects (WMO). It was decided that the research does not fulfill these conditions and therefore concluded that it is exempted for further approval by the ethical research committee. The study was carried out in accordance with the Dutch Public Health Act. Participation in the questionnaire was voluntary and online informed consent was obtained. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as [ClinicalTrials.gov][1]. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The datasets generated during and/or analysed during the current study are not publicly available but are available from the corresponding author on reasonable request. [1]: http://ClinicalTrials.gov