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Indoor Air. 2018 Jan;28(1):73-79. doi: 10.1111/ina.12406. Epub 2017 Aug 14.

Emission strength of airborne pathogens during toilet flushing.

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Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong.
City University of Hong Kong Shenzhen Research Institute, Shenzhen, China.
Queen Mary Hospital, Pokfulam, Hong Kong.
School of Public Health, The University of Hong Kong, Pokfulam, Hong Kong.


The flushing of toilets generates contaminated aerosols, the transmission of which may cause the spread of disease, particularly in the immunocompromised or the elderly. This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom-built toilet under a controlled environment. Flushing was activated by a flushometer operated at two pressure levels, 400 kPa (high pressure [HP]) and 200 kPa (low pressure [LP]), and by a water cistern tank placed 95 cm (high tank [HT]) and 46 cm (low tank [LT]) above the toilet seat. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=-0.919, P<.001; LP, r=-0.936, P<.001; HT, r=-0.967, P<.05) in the different conditions then tested. The emission strength in the HP condition was statistically greater than that in the LP condition, whereas the cistern tank system produced less emissions than the flushometer system, and tank height was not found to be a sensitive parameter.


airborne transmitted pathogens; emission strength; infectious diseases; size-resolved emissions; toilet flushing-generated water droplets; toilet hygiene

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