Evaluation of survival rates of airborne microorganisms on the filter layers of commercial face masks

Abstract

After the WHO designated COVID-19 a global pandemic, face masks have become a precious commodity worldwide. However, uncertainty remains around several details regarding face masks, including the potential for transmission of bioaerosols depending on the type of mask and secondary spread by face masks. Thus, understanding the interplay between face mask structure and harmful bioaerosols is essential for protecting public health. Here, we evaluated the microbial survival rate at each layer of commercial of filtering facepiece respirators (FFRs) and surgical masks (SMs) using bacterial bioaerosols. The penetration efficiency of bacterial particles for FFRs was lower than that for SMs; however, the microbial survival rate for all tested masks was >13%, regardless of filtration performance. Most bacterial particles survived in the filter layer (44%-77%) (e.g., the core filtering layer); the outer layer also exhibited significant survival rates (18%-29%). Most notably, survival rates were determined for the inner layers (<1% for FFRs, 3%-16% for SMs), which are in contact with the respiratory tract. Our comparisons of the permeability and survival rate of bioaerosols in each layer will contribute to bioaerosol-face mask research, while also providing information to facilitate the establishment of a mask-reuse protocol.

Comparison of bacterial filtration efficiency vs. particle filtration efficiency to assess the performance of non-medical face masks

“…Surgical masks are regulated as medical devices and FFP masks as respiratory protection device and are designed to meet more demanding performance criteria. In their work to evaluate the survival rate of bio aerosols on filter layers of FFPs and surgical masks, Jeong et al 12 showed that FFPs were more effective in physically blocking bio aerosols and thus showed lower portion of microbial viability compared to surgical masks.…”

Viability of Bacillus subtilis Cells in Airborne Bioaerosols on Face Masks

“…Jeong et al ( 2021) determined that the survival rates of Staphylococcus epidermidis in bioaerosols from facepieces and surgical mask filters to be 13% [20]. Lin et al (2017) also reported that the viability of airborne B. subtilis spores filtered on facepieces and surgical masks increased by over 100% when they were stored at 37 • C with a relative humidity of 95% for 24 h, i.e., in conditions similar to those of a used mask [21].…”

“…On the other hand, more such bioaerosols were trapped by the anti-droplet masks than passed through them due to the great filtration performance of these masks against airborne droplets containing bacteria. Nevertheless, wearing masks even with high filtration performance may also allow for the transmission of respiratory disease if these masks are inappropriately used, such as when their surfaces are touched by the hands of the user [20][21][22]. Therefore, misusing masks poses risks to health as a result of bioaerosols passing through them or from the survival of living components on the masks, or from both.…”

Optimization of Cabin Virus Transmission Suppression Technology Based on Hanging Curtain Physical Isolation

“…However, there are differences in filter efficiency and protective ability among the various types of masks on the market [13,14]. Researchers found that the survival rate of most bacterial particles in mask filtration layers (such as filter cores) can reach 44 to 77% [15]. Ordinary masks worn by most people are less effective at stopping microorganisms, and simply wearing a mask cannot guarantee absolute safety.…”