Next to the idea that we see many contraptions (you can’t even call them masks) we see many people with all kind of masks, in and outside our healthcare settings. Certainly after my last flight to a WHO meeting on COVID-19, I had the feeling that it is time to write about masks.

On my way to Geneva, the gentleman to my left (yes, thanks to a canceled flight, I was in the hated middle seat) was calm, sleepy and wearing a mask. The fellow on my right, clearly had the sniffles, came from somewhere far away and was spreading his respiratory secretions in all directions, including mine. I so wanted to pull of the mask from calm-sleepy-guy, to place it on the next-seat-germ-blower.

How easy could basic prevention be? Wouldn’t it be fantastic if people would adhere to simple principles of how to cough and sneeze in public: turn away from others, use a tissue or elbow, followed by hand hygiene? Why don’t the people on buses, trains and airplanes don’t know this? If in addition, anyone who is sick gets a surgical mask while in public, we might have a way of preventing (or at least delaying) the spread of respiratory viruses. Instead, masks are worn by the healthy, leaving the sick (and soon-to-be hospital patients) without the needed protection.

Talking about masks in healthcare; Nearly every country I know off, went for maximum safety, recommending FFP2 masks (similar to N95). I would have suggested to use FFP1 for the majority of cases, and FFP2 only during high-risk procedures. But how can I, if everyone else seems to go “full safety”. Another reason, why I believe that my idea wouldn’t have been too bad, is the high probability that soon we will have a shortage of FFP2 and will have to tell our HCWs that FFP1 and surgical masks are “equally save”. Yes, I can see how they believe me and willingly expose themselves to the increasing number of patients with less than previously needed PPE! I believe that we have valid reasons to consider evidence over maximum safety, and that while we didn’t even start to talk about discomfort and physical effects associated with prolonged use of FFP2.

Please find below a very small selection of some bullet points from the literature, referring to the above expressed opinions:

Jeffrey D. Smith et al.
• We identified 6 clinical studies (3 RCTs, 1 cohort study and 2 case–control studies) and 23 surrogate exposure studies. In the meta-analysis of the clinical studies, we found no significant difference between N95 respirators and surgical masks in associated risk of (a) laboratory-confirmed respiratory infection (RCTs: odds ratio [OR] 0.89, 95% confidence interval [CI] 0.64–1.24; cohort study: OR 0.43, 95% CI 0.03–6.41; case–control studies: OR 0.91, 95% CI 0.25–3.36); (b) influenza-like illness (RCTs: OR 0.51, 95% CI 0.19–1.41); or (c) reported work-place absenteeism (RCT: OR 0.92, 95% CI 0.57– 1.50).
• In the surrogate exposure studies, N95 respirators were associated with less filter penetration, less face-seal leakage and less total inward leakage under laboratory experimental conditions, compared with surgical masks.

Jefferson T et al.
• We found no evidence that the more expensive, irritating and uncomfortable N95 respirators were superior to simple surgical masks in protecting health care workers from acute respiratory infection.

Vittoria Offeddu et al.
• Compared to masks, N95 respirators conferred superior protection against clinical respiratory illness (RR = 0.47; 95% CI: 0.36–0.62) and laboratory-confirmed bacterial (RR = 0.46; 95% CI: 0.34–0.62), but not viral infections or ILI.
• Meta-analysis of observational studies provided evidence of a protective effect of masks (OR = 0.13; 95% CI: 0.03–0.62) and respirators (OR = 0.12; 95% CI: 0.06–0.26) against severe acute respiratory syndrome (SARS).

Shu-Ann Let et al.
• The protection provided by surgical masks against particles (0.04–1.3 𝜇m) is 8–12 times less than N95 FFRs, but they are both found to be equivalent for protection against influenza infection when the concentrations of infectious viruses are low
• Protection provided by both FFP respirators and surgical masks was not significantly affected by the particle size ranging from 0.093 to 1.61 𝜇m.
• Particle penetration through face seal leaks was greater than that through filter material (ed. fit more important than membrane)
• Respirators with the highest filtration efficiencies are not necessary having the best fit factors and protection factor

Jan Gralton et al.
• The protective effect of masks may only be apparent when mask use is bundled with other infection-control measures. Rather, a synergistic combination of mask use with, for example, the decontamination of hands before doffing masks or a comfortable mask that does not induce the need to adjust it, may better-protect HCW from infection than mask use alone.
• World Health Organization guidelines recommend surgical masks for all patient care with the exception of N95 masks for aerosol generating procedures. (ed. now under consideration)

Khai Tran et al.
• We identified 5 case-control and 5 retrospective cohort studies which evaluated transmission of SARS to HCWs. Procedures reported to present an increased risk of transmission included [n; pooled OR(95%CI)] tracheal intubation [n = 4 cohort; 6.6 (2.3, 18.9), and n = 4 case-control; 6.6 (4.1, 10.6)], non-invasive ventilation [n=2 cohort; OR 3.1(1.4, 6.8)], tracheotomy [n=1 case-control; 4.2 (1.5, 11.5)] and manual ventilation before intubation [n = 1 cohort; OR 2.8 (1.3, 6.4)].
• Other intubation associated procedures, endotracheal aspiration, suction of body fluids, bronchoscopy, nebulizer treatment, administration of O2, high flow O2, manipulation of O2 mask or BiPAP mask, defibrillation, chest compressions, insertion of nasogastric tube, and collection of sputum were not significant.
• Our findings suggest that some procedures potentially capable of generating aerosols have been associated with increased risk of SARS transmission to HCWs or were a risk factor for transmission, with the most consistent association across multiple studies identified with tracheal intubation.

Benjamin J. Cowling et al.
• We find that aerosol transmission accounts for approximately half of all transmission events. This implies that measures to reduce transmission by contact or large droplets may not be sufficient to control influenza A virus transmission in households.

References
1. Jeffrey D Smith et a. Effectiveness of N95 respirators versus surgical masks
in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis CMAJ, May 17, 2016, 188(8) 567
2. Jefferson T et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. Cochrane. https://www.cochrane.org/CD006207/ARI_physical-interventions-to-interrupt-or-reduce-the-spread-of-respiratory-viruses
3. Vittoria Offeddu et al. Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis. CID 2017:65;1934
4. Shu-Ann Lee et al. Particle Size-Selective Assessment of Protection of European Standard FFP Respirators and Surgical Masks against Particles-Tested with Human Subjects. Journal of Healthcare Engineering Volume 2016, Article ID 8572493, 12 pages http://dx.doi.org/10.1155/2016/8572493
5. Jan Gralton et al. Protecting healthcare workers from pandemic influenza: N95 or surgical masks? Crit Care Med 2010 Vol. 38, No. 2, p657
6. Khai Tran et al. Aerosol Generating Procedures and Risk of Transmission of Acute Respiratory Infections to Healthcare Workers: A Systematic Review. PLoS one April 2012 Volume 7, Issue 4, e35797
7. Benjamin Benjamin J. Cowling et al. Aerosol transmission is an important mode of influenza A virus spread. Nat Commun. 2013 ; 4: 1935. doi:10.1038/ncomms2922