Abstract
The coronavirus disease 2019 (COVID-19) pandemic is a general health crisis and has irreversible impacts on human societies. Globally, all people are at risk of being exposed to the novel coronavirus through transmission of airborne bioaerosols. Public health actions, such as wearing a mask, are highly recommended to reduce the transmission of infectious diseases. The appropriate use of masks is necessary for effectively preventing the transmission of airborne bioaerosols. The World Health Organization (WHO) suggests washing fabric masks or throwing away disposable masks after they are used. However, people often use masks more than once without washing or disposing them. The prolonged use of a single mask might—as a result of the user habitually touching the mask—promote the spread of pathogens from airborne bioaerosols that have accumulated on the mask. Therefore, it is necessary to evaluate how long the living components of bioaerosols can be viable on the masks. Here, we evaluated the viability of airborne Bacillus subtilis (B. subtilis) in bioaerosols filtered on woven and anti-droplet (non-woven) face masks. As a simulation of being simultaneously exposed to sand dust and bioaerosols, the viability rates of bioaerosols that had accumulated on masks were also tested against fine dust and airborne droplets containing bacteria. The bioaerosols survived on the masks immediately after the masks were used to filter the bioaerosols, and the bacteria significantly proliferated after one day of storage. Thereafter, the number of viable cells in the filtered bioaerosols gradually decreased over time, and the viability of B. subtilis in bioaerosols on the masks varied, depending on the mask material used (woven or non-woven). Despite the reduction in viability, bioaerosols containing living components were still found in both woven and anti-droplet masks even after six days of storage and it took nine days not to have found them on masks. The number of viable cells in bioaerosols on masks significantly decreased upon exposure of the masks to fine dust. The results of this study should provide useful information on how to appropriately use masks to increase their duration of effectiveness against bioaerosols.
Highlights
Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread around the world since the first case was identified in December 2019 [1]
As a simulation of coughing, speaking, and sneezing conditions, airborne droplets containing B. subtilis cells were sprayed into the face masks through a filtration system, and the longevity of bacteria on the masks was measured by culturing B. subtilis in bioaerosol (Figure 1)
The numbers of viable B. subtilis cells obtained from the masks immediately after they were exposed to the sprayed bioaerosols and after culturing were in the range 1.8–8.3 × 103 colony forming units (CFU)/cm2; with the larger number observed, at day 0, for the anti-droplet masks than for the woven masks (Figures 2a and 3a)
Summary
Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread around the world since the first case was identified in December 2019 [1]. COVID-19 is an ongoing global pandemic and over 4.57 million deaths among 221 million confirmed cases have been reported to the World Health Organization (WHO) as of 7 September 2021 [2]. The SARS-CoV-2 virus causing COVID-19 is mainly transmitted from an infected person to another person in close contact. The infected people release respiratory droplets and aerosol particles when they cough, sneeze, speak, sing, or breathe. A combination of public health actions is necessary to reduce the spread of infectious diseases such as COVID-19
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