An expert brief by IPC Physician Dr. Dan Lebowitz
This is how I would summarize what I read, heard, saw for the past couple of weeks and went through myself as a clinician regarding the passionate debate over small particle aerosolization vs. large droplet transmission and use of a medical mask vs. respirator:
- Studies show that aerosolization of small particles (cutoff about 5um) containing respiratory viruses can occur.
- SARS/MERS: specific events, notably hospital superspreading events regarding SARS, (Toronto hospitals, 138 patients in HK hospital) and MERS (South-Korea) have suggested possible airborne spread; but it seems that factors such as failure to implement strict isolation of patients, poor communication and knowledge of patient movement between hospitals, overcrowding in emergency room, inadequate ventilation, limited availability of isolation rooms in ER (Lancet Hui 2016 for SARS), unprotected aerosolization procedures (notably for SARS) are great contributors to nosocomial events. Regarding Amoy Gardens, Yu NEJM 2004’s modeling is consistent with airborne spread, but – just as everything in medicine (and life) – this remains uncertain.
- SARS CoV-2: There is no evidence/suspicion of airborne spread to this date; report of infected Japanese healthcare workers managing cases of diamond princess using med mask (CIDRAP news).
- Randomized controlled trails (Loeb et al JAMA 2009, Radanovitch JAMA 2019 for influenza) have not shown benefit of N95 over surgical masks for transmission of influenza/other viral infections in healthcare workers.
- Masks and handwashing prevent SARS in healthcare workers (Seto Lancet 2003).
- Jefferson Cochrane 2011 concludes that: wearing a surgical mask or N95 is measure with the most supportive evidence to reduce viral transmission (although some studies question even that). No advantage was shown of N95 over surgical masks in reducing viral transmission.
- N95 has disadvantages: training is necessary for proper donning (seal check, etc.) They are uncomfortable for regular use Improper wearing or adjustment because of discomfort could lead to face contamination and an increased risk due to a false sense of security.
- SARS CoV-2: despite absence of evidence supporting N95 over surgical masks, only the WHO guidelines recommend use of surgical mask except when performind “aerosolization procedures”, because lack of evidence for superiority of the N95 as well as the WHO’s target to include low and middle income countries. All other guidelines recommend universal N95 masking (CDC, ECDC, UK, HUG, OFSP hospital setting).
If I had to conclude:
- Combination of adequately applied measures, mainly hand hygiene + any mask (N95 or SM) is the most important intervention, debate over which type of spreading/mask might be marginal -knowledge gaps/areas of scientific uncertainties + basic human psychology/anxiety + media pressure + being in a high resource setting allows/motivates us to recommend universal N95. We should just bear in mind that the most bearded among us (and others misusing theses masks) in fact us it as a surgical mask…
- From a psychological standpoint I’m (unsurprisingly) impressed how that debate is intense and has been ongoing for decades!