Looks like just about every risk factor was present in the setting: a lot of people close together indoors poor ventilation long duration singing Google Translate :  The Public Health Agency assumes that the contagion took place during the general rehearsal that the choir did on Friday, September 11 in a place of La Fàbrica while preparing the concert that took place the following Sunday during the Festa Major of Sallent. An exposure of more than 15 minutes, in a room with closed windows, with insufficient physical distance, with working air conditioning, which favors the suspension of particles by aerosol in a closed cycle, and the fact that many of the singers do not they wore masks, it potentiated the almost general contagion in an environment where it was sung, they have claimed. Choir members have explained that they closed the windows because there was a plague of boxwood butterflies outside, and that once closed, they turned on the air conditioning. Video of the e...

Nursing homes are the most common setting for superspreading events in the database. How can the virus spread so easily in them? A confidential report of the Dutch scientific advisory board RIVM may provide an answer. It states that the HVAC system in a nursing home in the Netherlands likely caused an outbreak that infected up to 21 residents and 18 staff members. Below is a (slightly manually improved) Google Translate of an article in Dutch newspaper De Volkskrant. The main findings that are suggestive of aerosol transmission via the HVAC system: - All staff members in the nursing home wore surgical masks (except during breaks) - Only one patient was initially infected but the virus then spread rapidly throughout the facility - The virus was found in high values ​​on the mesh covers of the air-conditioning unit and in filters of four ventilation cabinets.

Detailed investigation of a superspreading event in a meat processing plant in Germany: