Controversies in Respiratory Protective Equipment Selection and Use During COVID-19

The evidence base evaluating continuous vs targeted use of RPE in healthcare settings is quite small. Continuous use refers to using the RPE during an entire shift, whereas targeted use involves using RPE only when caring for confirmed or suspected respiratory patients. In our literature review we identified only one RCT that included separate study arms for continuous and targeted N95 respirator use.¹³ The authors found a significantly lower rate of clinical respiratory illness among HCWs in the continuous-use group, compared with that in the targeted-use group. Limitations of the study included a relatively short follow-up of 4 weeks and uneven distribution of baseline characteristics, although the authors adjusted for these differences in their analysis. The study, however, did not compare continuous vs targeted use of surgical masks with regard to clinical outcomes. Based on the study results, we can only infer that continuous use of RPE, either surgical mask or N95 respirator, may provide additional benefit to HCWs vs targeted use only.

Given the lack of robust evidence informing continuous or targeted RPE use, we suggest some additional factors to guide decision making. In settings with high HCW compliance with universal RPE (above 50%), even noncompliant HCW are protected against clinical respiratory illness, which suggests a herd protective effect when universal RPE use is implemented, likely owing to the prevention of symptomatic or asymptomatic infectious spread among HCWs.¹⁴ It is important to note that the compliance rate may be limited by discomfort of prolonged wear of certain RPEs. One study reported that compliance rate is lower for continuous use (66%) than it is for targeted use (82%).¹³ Accumulated respiratory pathogen deposition on RPEs from an extended period of use that could result in self-­contamination to the wearer is a potential concern, although these risks must be balanced against the repeated donning and doffing required by targeted use. Pilot studies examining viral particles left on surgical masks after being worn for entire shifts (or as long as tolerated) found that there were significantly more viral particles detected after 6 hours of continuous wear, which may increase the risk of self-contamination.¹⁵

The current literature is applicable to infections that are known to spread via droplet contact, and this is a major limitation in generalizing the available evidence to the SARS-CoV-2 pandemic, in which debate persists regarding the exact mode of transmission. It is postulated that, even in infections traditionally considered to be spread by droplets, such as influenza, aerosol transmission may occur when HCWs are working in close proximity to the exposure source or when the droplet evaporates and becomes droplet nuclei. The United States National Academies of Science, Engineering, and Medicine expert consultation report, published in April 2020, concluded that current studies support the possibility of aerosolization of SARS-CoV-2 virus from normal breathing.¹⁶ As of April 2020, the WHO recommendation for SARS-CoV-2 is to use droplet contact precautions with a surgical mask for regular patient care and N95 respirator for aerosol-generating procedures.¹ Although we have not come across any studies specifically comparing the efficacy between surgical mask to N95 respirator protection while performing aerosol-generating procedures, a systematic review found that certain aerosol-generating procedures, such as endotracheal intubation and noninvasive ventilation, conferred a significantly higher risk of transmission of SARS-CoV-1 to HCWs in 2003.¹⁷ For the current crisis, the CDC is taking a cautious approach in which N95 respirators are recommended for HCWs caring for patients with confirmed or suspected SARS-CoV-2 infection if the supply chain is secure, with advice in place in times of RPE shortage, such as use of expired respirators, other types of equivalent respirators, or respirators not approved by the National Institute for Occupational Safety and Health, as well as optimization of administrative and engineering controls (eg, telemedicine, limiting patient and visitor numbers, physical barriers, optimizing ventilation systems).^2,18 This advice is unusual in terms of deviating from advising the most appropriate RPE, and we presume it reflects the present global supply problems.