Toilet Flushing Creates Aerosol Cloud That Can Spread Germs

Flushing a toilet can create a cloud of germ-laden droplets and particles that can rise to face level, travel up to 1.5 meters, and linger in the air for at least 20 seconds, according to a new study. These aerosols can potentially spread bacteria and viruses, including Legionnaires' disease, influenza, and norovirus.

The research, published in Science of the Total Environment, analyzed 22 studies on aerosol formation during toilet flushing. Scientists investigated factors like toilet design, flush volume, water pressure, ventilation, and whether the lid was closed.

Aerosols, tiny airborne particles, can carry microorganisms from the flush water or toilet bowl. Most particles measured were between 0.3 and 10 micrometers, with many under 3 micrometers. They can reach heights of up to 1.63 meters, posing a risk to adults' breathing zones, and samples taken at toilet seat height correspond to the breathing zone of young children.

The study found that higher concentrations of microorganisms in the flush water and larger flush volumes increase aerosolization. A tenfold increase in microbial concentration boosted aerosols 2.6 times, while each extra liter of flush water increased them 1.3 times. Toilet design, specifically the gaps between the seat and bowl, also influences particle escape.

While closing the toilet lid before flushing can reduce airborne biological aerosols by 23 times compared to flushing with the lid open, scientists are not yet certain of its effectiveness. They suggest the lid may redirect aerosols rather than prevent their formation, with some still escaping through gaps. However, they recommend closing the lid as a precautionary measure.

Ventilation, such as a working fan or open window, helps clear aerosols from the air more quickly. The study highlights that while domestic toilets may pose little risk to healthy individuals, the risk is higher in hospitals and nursing homes. In public restrooms, frequent flushing can increase particle spread and infection risk. The research demonstrates a potential transmission mechanism but does not confirm that flushing directly causes infections.

Dr. Dana Dror, a therapist and infectologist at Clalit Health Services, stated that while the study shows microorganisms can enter the air during flushing, the actual risk of infection in everyday conditions is currently unknown.