ABSTRACT
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.
Subject(s)
Coronavirus InfectionsABSTRACT
Background Evidence for indoor airborne transmission of SARS-CoV-2 is accumulating. If SARS-CoV-2 also spreads via aerosols, this has implications for measures taken to limit transmission. Objectives The aim of this study is to assess exposure to airborne SARS-CoV-2 particles from breathing, speaking, coughing and sneezing in an indoor environment. Methods An exposure assessment model was developed to estimate numbers of SARS-CoV-2 particles in aerosol droplets, expelled during breathing, speaking, coughing and sneezing by an infected person in an unventilated indoor environment, and subsequent inhalation by one or more persons. Scenarios encompass a range of virus concentrations, room sizes and exposure times. Results The calculated total volume of expelled aerosol droplets was highest for a sneeze, followed by a cough and speaking for 20 minutes, and lastly breathing for 20 minutes. A few to as much as tens of millions of virus particles were expelled. Exposure probability strongly depends on the viral concentration in mucus, as well as on the scenario. Exposure probabilities were generally below 1% at a virus concentration in mucus below 10^5 per mL for all scenarios, increasing steeply at different higher concentrations. According to nose / throat swab data collected from patients, 75%, 50% and 5% of infected individuals carry an estimated number of SARS-CoV-2 per mL mucus of at least 10^5, 10^6 and 10^8, respectively. Discussion Exposure to SARS-CoV-2 via aerosols generated during breathing, speaking, coughing and sneezing in an unventilated indoor environment is possible. This study forms a basis to estimate probabilities of exposure to SARS-Cov-2 by airborne transmission in indoor spaces. As long as it is uncertain what fraction of the airborne virus particles is infectious and as long as a dose response relation is lacking, it is recommended to be precautious.