Effect of wearing N95 facemasks on the mode of transmission of SARS-CoV-2 in the indoor environment of a hospital

Omicron, a mutant strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread around the world largely because of its potent immune evasion. However, the transmission mode of SARS-CoV-2 remains ambiguous. In this study, three distinct interior hospital environments were selected for surface and airborne viral sampling to ascertain the impact of wearing an N95 facemask on the spread of the virus. SARS-CoV-2 RNA was detectable in the air of an emergency intensive care unit corridor, where over 30% of mobile personnel did not wear N95 facemasks strictly. By contrast, SARS-CoV-2 RNA was not detectable in the air of a geriatric respiratory diseases ward or in that of an emergency laboratory, where N95 facemasks were mandatory for both mobile staff and patients. Additionally, SARS-CoV-2 RNA was detected in all object surface samples collected in this study (p < 0.05). These results indicate that surface contact transmission should be further investigated as a possible mode of SARS-CoV-2 transmission and that the strictness of N95 facemask usage may influence indoor transmission of aerosol-dominated types of SARS-CoV-2. The present findings could contribute to reducing the spread of both SARS-CoV-2 and other respiratory diseases and could advance the understanding of how SARS-CoV-2 spreads.