In March 2020, a large number of critical acute respiratory syndrome coronavirus (SARS-CoV-2) infections occurred in an unusual shortage of personal protective equipment (PPE) for clinicians and essential healthcare workers. The demand was most profound among COVID-19 face masks. N95 respirators, selected for their ability to filter 95% or more of tiny 0.3-μm particles, are the strength of protection on airborne pathogens.
Airborne transmission results from touch with infectious particles contained within small (<5 μm) droplet nuclei (i.e., aerosols) that can linger in the air for hours and be scattered over great distances. In distinction, SARS-CoV-2 is primarily spread by large (>5-10 μm) respiratory droplets that can be suspended up to 6 feet horizontally and drop to the ground within moments, against which surgical masks usually offer adequate protection.
Nonetheless, the Centers for Disease Control and Prevention suggests that health care workers use more robust COVID-19 face masks, such as N95 masks when caring for patients with established or suspected coronavirus disease 2019 (COVID-19) out of concern for airborne transmission, especially during vulnerability to procedures that allow high concentrations of aerosols (e.g., extubation, intubation,noninvasive ventilation). To alleviate the deficit of N95 respirators, many health care facilities are seeking nonstandard approaches to keeping an adequate supply, including mask decontamination and reprocessing for reuse, which increase the wearable life of the mask beyond the demise date, and procuring KN95 masks (N95 masks that are regulated in China).
In JAMA Internal Medicine, Sickbert-Bennett and colleagues provide a reassuring indication of the performance of nonstandard procedures to preserving the N95 mask supply. The authors' laboratory-based evaluation of a broad array of nonstandard face masks proves that the National Institute for Occupational Safety and Health (NIOSH)-approved N95 respirators outperform options filtration performance. The study results showed that N95 masks reprocessed using ethylene oxide sterilization and masks that are up to 11 years past expiration control very high filtration performance under laboratory conditions.
N95 masks with suboptimal fit still had comparable filtration effectiveness of more than 90%. Their KN95 counterparts, millions of obtained by or distributed to US hospitals, worked less well, with filtration effectiveness ranging from 53% to 85%. Surgical masks obtained with either ties or ear loops also had much lower filtration effectiveness of 37% to 69%, as expected by their more comfortable, thinner filter and looser fit.
Notwithstanding the apparent imperfect filtration efficiency of non-NIOSH approved respirators and surgical masks in the laboratory, there is a reason for optimism concerning their real-world effectiveness. Although surgical masks have decreased filtration efficiency than N95 respirators, observational studies have shown no significant advantage of N95 masks over surgical masks for prevention of critical acute respiratory syndrome coronavirus (odds ratio, 0.86; 95% CI, 0.22-3.33) or other respiratory viruses (odds ratio, 0.96; 95% CI, 0.85-1.08). For healthcare workers, routine care for a patient with COVID-19 cannot be viewed as high-risk occupational exposure if both are wearing surgical masks.
Yet, SARS-CoV-2 viral particles have been recognized in the air for several hours after an aerosolizing event simulated in a laboratory and near air vents in a clinical setting. A group of 239 scientists newly signed an open letter urging the World Health Organization and other international public health bodies to suggest additional precautions (though not COVID-19 face masks specifically) to protect against potential airborne transmission, highlighting several recent super spreading events in which SARS-CoV-2 transmission occurred in poorly ventilated areas.
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