Background
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.