STUDY: measurement of facemask efficacy for filtering expelled droplets during speech

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STUDY: measurement of facemask efficacy for filtering expelled droplets during speech

The global spread of COVID-19 in early 2020 has significantly increased the demand for face masks around the world, while stimulating research about their efficacy. Here we adapt a recently demonstrated optical imaging approach (1, 2) and highlight stark differences in the effectiveness of different masks and mask alternatives to suppress the spread of respiratory droplets during regular speech.

In general, the term ‘face mask’ governs a wide range of protective equipment with the primary function of reducing the transmission of particles or droplets. The most common application in modern medicine is to provide protection to the wearer (e.g., first responders), but surgical face masks were originally introduced to protect surrounding persons from the wearer, such as protecting patients with open wounds against infectious agents from the surgical team (3), or the persons surrounding a tuberculosis patient from contracting the disease via airborne droplets (4).

This latter role has been embraced by multiple governments and regulatory agencies (5), since COVID-19 patients can be asymptomatic but contagious for many days (6). The premise of protection from infected persons wearing a mask is simple: wearing a face mask will reduce the spread of respiratory droplets containing viruses. In fact, recent studies suggest that wearing face masks reduces the spread of COVID-19 on a population level, and consequently blunts the growth of the epidemic curve (7, 8).

Still, determining mask efficacy is a complex topic that is still an active field of research (see for example (9)), made even more complicated because the infection pathways for COVID-19 are not yet fully understood and are complicated by many factors such as the route of transmission, correct fit and usage of masks, and environmental variables.

From a public policy perspective, shortages in supply for surgical face masks and N95 respirators, as well as concerns about their side effects and the discomfort of prolonged use (10), have led to public use of a variety of solutions which are generally less restrictive (such as homemade cotton masks or bandanas), but usually of unknown efficacy.

While some textiles used for mask fabrication have been characterized (11), the performance of actual masks in a practical setting needs to be considered. The work we report here describes a measurement method that can be used to improve evaluation in order to guide mask selection and purchase decisions.

 

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