It is therefore important to understand the efficacy of masks and face coverings of different types in reducing outward transmission of aerosols and droplets from expiratory activities. There have been indications of asymptomatic carriers of COVID-19 infecting others 18, 19, 20, leading to increasing, albeit inconsistent 21, 22, 23, 24, calls for more universal wearing of masks or face coverings by the general public to help control disease transmission during pandemics. Alternatively, masks can potentially reduce outward transmission by infected individuals, providing protection to others 7, 16, 17. Much research has indicated that masks can provide significant protection to the wearer, although proper mask fitting is critical to realizing such benefits 12, 13, 14, 15. Consequently, the wearing of masks-in addition to vigilant hand hygiene-has been put forth as a means to mitigate disease transmission, especially in healthcare settings 8, 9, 10, 11. Uncertainty remains regarding the role and spatial scale of these different transmission modes (contact, droplet spray, or aerosol inhalation) for specific respiratory diseases, including for COVID-19 3, 4, 5, 6, 7, in particular settings, but airborne transmission stems from the initial expiratory emission of aerosols or droplets.
Transmission of viruses in emitted droplets and aerosols to susceptible individuals may occur via physical contact after deposition on surfaces, reaerosolization after deposition, direct deposition of emitted droplets on mucosal surfaces (e.g., mouth, eyes), or direct inhalation of virus-laden aerosols 1, 2. Further work is needed to establish the efficacy of cloth masks at blocking expiratory particles for speech and coughing at varied intensity and to assess whether virus-contaminated fabrics can generate aerosolized fomites, but the results strongly corroborate the efficacy of medical-grade masks and highlight the importance of regular washing of homemade masks.Īirborne transmission of infectious respiratory diseases involves the emission of microorganism-containing aerosols and droplets during various expiratory activities (e.g., breathing, talking, coughing, and sneezing). Audio analysis of the speech and coughing intensity confirmed that people speak more loudly, but do not cough more loudly, when wearing a mask. In contrast, shedding of non-expiratory micron-scale particulates from friable cellulosic fibers in homemade cotton-fabric masks confounded explicit determination of their efficacy at reducing expiratory particle emission.
These masks similarly decreased the outward particle emission of a coughing superemitter, who for unclear reasons emitted up to two orders of magnitude more expiratory particles via coughing than average. Both surgical masks and unvented KN95 respirators, even without fit-testing, reduce the outward particle emission rates by 90% and 74% on average during speaking and coughing, respectively, compared to wearing no mask, corroborating their effectiveness at reducing outward emission. Here, we measured outward emissions of micron-scale aerosol particles by healthy humans performing various expiratory activities while wearing different types of medical-grade or homemade masks. Although mask wearing is intended, in part, to protect others from exhaled, virus-containing particles, few studies have examined particle emission by mask-wearers into the surrounding air. In response to shortages, many public health authorities have recommended homemade masks as acceptable alternatives to surgical masks and N95 respirators. The COVID-19 pandemic triggered a surge in demand for facemasks to protect against disease transmission.
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