Covid-19 airborne transmission and its prevention: waiting for evidence or applying the precautionary principle?

Reason #1: description of an index case but without confirmed secondary cases Buchholz U, Müller MA, Nitsche A, et al. Contact investigation of a case of human novel coronavirus infection treated in a German hospital, October-November 2012. Euro Surveill. 2013;18(8):20406. Published 2013 Feb 21. Lillie PJ, Samson A, Li A, et al. Novel coronavirus disease (Covid-19): The first two patients in the UK with person to person transmission. J Infect. 2020;80(5):578-606. doi:10.1016/j.jinf.2020.02.020; Park BJ, Peck AJ, Kuehnert MJ, et al. Lack of SARS transmission among healthcare workers, United States. Emerg Infect Dis. 2004;10(2):244-248. doi:10.3201/eid1002.030793; Reuss A, Litterst A, Drosten C, et al. Contact investigation for imported case of Middle East respiratory syndrome, Germany. Emerg Infect Dis. 2014;20(4):620-625. doi:10.3201/eid2004.131375.


Animal CoVs
PRCoV Nonhealthcare setting (USA): 46 pigs artificially infected. Oral-nasal swabs, expired air by the pigs, air samples from the room.
AGI-30 impinger using viral growth media as collection fluid ( Influenza genome was the most detected (20.6% of total samples). HCoV was not found.

SARS-CoV
Room with positive patient in the Chang Gung Memorial Hospital (Taiwan): 12 air samples and 3 unexposed filters.

Tsai at al., 2006 [71]
Healthcare setting (Taiwan): -6 air samples from negative pressure hospital isolation room; -3 air samples from each filter during experimental tests for filtration efficiency.
Sampling filter cassette with a 1-µm PTFE filter were collected from a patient isolation room

MERS-CoV
Healthcare setting (South Korea): 7 air and 68 surfaces samples from 2 rooms of infected patients in hospital A and 1 room patient in hospital B MD8 airscan sampling device with 3-µm pore size sterile gelatin filters (50 L/min, 20 min). RT-PCR and isolation on cells. Electron microscope and immunofluorescence assay All air samples positive and 4/7 infectious. 42/68 swab samples positive by RT-PCR and sequencing. Kim et al., 2016 [74] Camels' barn (Saudi Arabia): 3 air samples from the site where a worker became ill MD8 airscan sampling device with 3-µm pore size sterile gelatin filters (50 L/min, 20 min). Real time RT-PCR and sequencing Only one air sample positive and the genome sequences were identical to those from the animal and from the infected worker. Healthcare setting (China): 35 air samples collected with different sampling methods in two designated hospitals and public areas in Wuhan Sampling on presterilized gelatin filters (pore size 3 µm) with three methods: -Aspiration using Casella portable pump (5 L/min, 5-20 hr) for aerosol samples of total suspended particles (30); -Miniature SKC cascade impactor (9 L/min, 5-20 hr) for aerodynamic size-segregated aerosol samples (3); -Gelatin filter packed in a holder with an effective deposition area of 43 cm 2 (exposed for 7 days) for aerosol deposition samples (2) Droplets digital PCR.
Highest level contamination in the toilet area. Positive samples in the medical staff area and low contamination in public area outside. RNA was found in submicron region and supermicron region aerosol size. Liu et al., 2020 [76] Healthcare setting (Singapore): 6 air samples from three AIIRs and 38 surfaces samples (surface inside the room and personal protective equipment used by medical staff) SKC filter cassette preloaded with 0.3-µm pore size PTFE filter (5 L/min, 4 hr) in the room and anteroom. Sartorius MD8 microbiological sampler with gelatin membrane filter (6 L/h, 15 min) outside the room.
NIOSH BC 251 bioaerosol sampler separating particles into 3 size intervals (3.5 L/min, 4 h). In one patient room, additional sampling with SKC filter cassette preloaded with 0.3-µm pore size PTFE filter (5 L/min, 4 h). RT-PCR and real time RT-PCR Air samples from two (66.7%) of AIIRs resulted positive in particle sizes > 4 µm and 1-4 µm. Rooms with contaminated air had also surface contamination.