Bioaerosol emissions during toilet flushing are an often-overlooked source of potential health risks in shared public facilities. A new study published in Risk Analysis found that bioaerosol concentrations of two bacteria -- Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) -- exceeded acceptable levels established by the Centers for Disease Control (CDC) after toilet flushing. Inhaling these biological particles can produce symptoms like abdominal cramps, nausea, diarrhea, and vomiting.
The research was conducted in two restrooms located in an office building in China. One contained a squat toilet and the other a bidet toilet. Scientists measured the emissions of bioaerosols containing S. aureus and E. coli under various flushing conditions and ventilation scenarios in both restrooms. An analysis of the results showed that, compared to bidet toilets, squat toilets generated 42 to 62 percent higher concentrations of S. aureus bioaerosols and 16 to 27 percent higher concentrations of E. coli bioaerosols.
In addition, bioaerosol concentrations were 25 to 43 percent (S. aureus) and 16 to 27 percent (E. coli) lower after the first flush of an empty toilet compared to those observed after a second flush (when feces were present).
Importantly, the researchers found that active ventilation with an exhaust fan reduced the risk by 10 times.
"Our findings underscore the substantial health risks posed by bioaerosol exposure in public washrooms," says lead author Wajid Ali, a PhD student in environmental studies at China University of Geosciences. "Enhancing ventilation systems by optimizing exhaust fan efficiency and air exchange rates can effectively reduce bioaerosol concentrations and exposure risks for the public."
He adds that the findings for squat toilets apply for seated toilets as well. For public health policymakers, the results of the study provide evidence-based recommendations to define safe bioaerosol exposure limits and promote hygiene practices in public washrooms, ensuring healthier and safer indoor environments.
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