Cotton and surgical face masks in community settings: bacterial contamination and face mask hygiene. Microbiological study on face masks

During the current COVID-19 pandemic, the use of protective face masks has become increasingly recommended and even mandatory in community settings. To have a better idea of the risk of bacterial cross-contamination when wearing such masks, this study analyzed the bacterial bioburden of certified disposable surgical masks and homemade cotton masks, and surveyed the habits and face mask preferences of the Flemish population. Using culture approaches and 16S rRNA gene amplicon sequencing, we analyzed the microbiome of surgical and/or cotton face masks of 13 healthy volunteers after 4 hours of wearing. After 4 hours of wearing, cotton and surgical masks contained on average 1.46x105 CFU/mask and 1.32x104 CFU /mask respectively. Bacillus, Staphylococcus and Acinetobacter spp. were mostly cultured from the masks, and 43 % of these isolates were resistant to either ampicillin or erythromycin. DNA-based amplicon sequencing analysis of the masks demonstrated a consistent microbiome difference between mask types. Cotton masks mainly contained Roseomonas, Paracoccus and Enhydrobacter taxa, whereas surgical masks contained mostly Streptococcus and Staphylococcus. After 4 hours of mask wearing, the microbiome of the anterior nares and the cheek showed a trend towards an altered beta-diversity based on 16S rRNA gene amplicon sequencing. According to dedicated questions in the large-scale Corona survey of the University of Antwerp with almost 25,000 participants, only 21% of responders reported to clean their cotton face mask daily as was recommended by governmental instructions. Laboratory results indicated that the best mask cleaning methods were boiling at 100° C, washing at 60° C with detergent or ironing with a steam iron. Taken together, the results of this study suggest that a considerable number of bacteria, including pathobionts and antibiotic resistant bacteria, accumulate on surgical and even more on cotton face masks after 4 hours of wearing. Based on our results, face masks should be properly disposed of or sterilized after 4 h of intensive use. Clear guidelines for the general population are crucial to reduce the bacteria-related biosafety risk of face masks, and measures such as physical distancing and increased ventilation should not be neglected when promoting face mask use.