Spread of bidet toilet flushing-generated infectious aerosols in the cubicle of a public restroom

Abstract

In public restrooms cubicles, flushing bidet toilets can generate infectious aerosols, potentially spreading of bacteria, viruses, and other pathogens. This study examines aerosol dispersion during bidet toilet flushing with the lid open and closed. Fluorescein sodium, simulating fecal matter, was seeded into the bidet toilet before flushing. Fluorescence intensity on surfaces, including the flush button, toilet lid, floor, walls, and breathing zone, was monitored, while aerosol concentrations (PM_2.5 and PM₁₀) were measured by TSI dusttrak. Due to the limitations of aerosol sampling instruments, fluorescein sodium was used as a tracer to provide more cumulative and representative data. Results showed that aerosol deposition was significantly higher with the lid open, with total surface deposition 2.27 times greater than when closed. It is recommended to flush toilets with lids closed. If the lid must be opened, users should avoid touching the flush button and back right of the lid directly. When the previous user closes the toilet lid to flush, the next user should avoid touching the front right of the lid. With the lid open, the deposition of aerosols in the breathing zone decreased by 80.99% (log reduction = 0.72) at the 2nd minute compared to the peak in the 1st minute after flushing. Users are recommended to wait for 2 min after the early flush before entering bidet toilet cubicles. When covering the toilet lid, there was no significant aerosol deposition in the breathing zone. This further highlights the importance of flushing with the lid closed.