Super spreading events and the development of the COVID-19 pandemic: what is the role of indoor air quality?
Recent studies of super spreading events have demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking and coughing in microdroplets small enough to remain airborne and pose an exposure risk when carrying a high virus load. However, the contribution of aerogenic transmission remains a controversial topic in the spread of the SARS-CoV-2 virus. In March-April 2020 there were reports of certain events where many persons were linked to the same source of infection. Such super spreaders were linked to après-ski-bars in Austria, Karaoke bars in South Korea, churches and other gatherings where many persons meet in confined poorly ventilated rooms. After the first wave households and certain workplaces were reported to be hotspots. Large groups of hundreds of workers in certain production facilities like slaughter houses, fish factories, textile sweat shops and cooled sorting and storage of fruits were reported as hot spots of infections in the aftermath of the first wave. In these settings airborne transmission may not always be the only transmission route but certainly an important explanation of the spatial patterns of group infections. On July 6th 2020 a group of 239 scientist published an open letter ‘It is Time to Address Airborne Transmission of COVID-19’ in Clinical Infectious Diseases (see https://academic.oup.com/cid/article/doi/10.1093/cid/ciaa939/5867798). The next day the WHO announced to take this message seriously and study the possibility of this third route of transmission in addition to transmission by direct contact and by fomite.
What can the super spreading events tell us about the role of the indoor air quality in the development of the pandemic. Based on the analysis of a range of such spreading events a pattern occurs that relates to conditions such as high occupancy, poor supply of fresh air and some specific activities such as talking loud and singing. What can super spreading events learn us about the transmission of the virus? How did they contribute to the pandemic in early 2020 and how important are these events overall future development of the endemic, including their potential role in next waves? How can sufficient and effective ventilation and regulated occupancy contribute to reducing the indoor risk of infection?