Respiratory source control using a surgical mask: An in vitro study

Abstract

Cough etiquette and respiratory hygiene are forms of source control encouraged to prevent the spread of respiratory infection. The use of surgical masks as a means of source control has not been quantified in terms of reducing exposure to others. We designed an in vitro model using various facepieces to assess their contribution to exposure reduction when worn at the infectious source (Source) relative to facepieces worn for primary (Receiver) protection, and the factors that contribute to each. In a chamber with various airflows, radiolabeled aerosols were exhaled via a ventilated soft-face manikin head using tidal breathing and cough (Source). Another manikin, containing a filter, quantified recipient exposure (Receiver). The natural fit surgical mask, fitted (SecureFit) surgical mask and an N95-class filtering facepiece respirator (commonly known as an “N95 respirator”) with and without a Vaseline-seal were tested. With cough, source control (mask or respirator on Source) was statistically superior to mask or unsealed respirator protection on the Receiver (Receiver protection) in all environments. To equal source control during coughing, the N95 respirator must be Vaseline-sealed. During tidal breathing, source control was comparable or superior to mask or respirator protection on the Receiver. Source control via surgical masks may be an important adjunct defense against the spread of respiratory infections. The fit of the mask or respirator, in combination with the airflow patterns in a given setting, are significant contributors to source control efficacy. Future clinical trials should include a surgical mask source control arm to assess the contribution of source control in overall protection against airborne infection.

To mask or not to mask: Modeling the potential for face mask use by the general public to curtail the COVID-19 pandemic

“…Indeed, if there is any asymmetry in outward vs. inward mask effectiveness, inward effectiveness is actually slightly preferred, although the direction of this asymmetry matters little with respect to overall epidemiologic outcomes. At least one experimental study [11] does suggest that masks may be superior at source control, especially under coughing conditions vs. normal tidal breathing and so any realized benefit of masks in the population may still be more attributable to source control. This is somewhat surprising, given that ϵ o appears more times than ϵ i in the model terms giving the forces of infection, which would suggest outward effectiveness to be of greater import at first glance.…”

“…Our theoretical results still must be interpreted with caution, owing to a combination of potential high rates of noncompliance with mask use in the community, uncertainty with respect to the intrinsic effectiveness of (especially homemade) masks at blocking respiratory droplets and/or aerosols, and even surprising amounts of uncertainty regarding the basic mechanisms for respiratory infection transmission [4,41]. Several lines of evidence support the notion that masks can interfere with respiratory virus transmission, including clinical trials in healthcare workers [3,4], experimental studies as reviewed [12,10,9,15,11], and case control data from the 2003 SARS epidemic [1,2]. Given the demonstrated efficacy of medical masks in healthcare workers [3], and their likely superiority over cloth masks in [5], it is clearly essential that healthcare works be prioritized when it comes to the most effective medical mask supply.…”

Facial protection for healthcare workers during pandemics: a scoping review

“…16 Addition of a peripheral Vaseline barrier has been shown to prevent peripheral air leakage and reduce exposure to airborne viral particles, making this a potential compensatory strategy when fit testing is not feasible. 17 Further evidence regarding mask fit in the inpatient setting is presented in the next section. The use of face shields as an adjunct to medicalgrade masks has been employed during the COVID-19 pandemic.…”

The Time for Universal Masking of the Public for Coronavirus Disease 2019 Is Now

“…Although the airborne versus droplet question is relevant to healthcare settings (which involve close contact) and has guided infection control recommendations and type of masks required accordingly [7,10], the most compelling reason for public masking is due to the data on spread from asymptomatic individuals [11]. For the general public, surgical isolation masks (as part of an overall public health strategy) should be able to curb dissemination of both droplet-spread and airborne viruses to the breathing zones of nearby individuals [12][13][14][15][16][17].…”