The study, published in the journal Physics of Fluids, used computer models to simulate water and air flows in a flushing toilet and the resulting droplet cloud. The researchers used a standard set of fluid dynamic formulas, known as the Navier-Stokes equations, to simulate flushing in two types of toilet -- one with a single inlet for flushing water, and another with two inlets to create a rotating flow. 

They also used a discrete phase model to simulate movement of the numerous tiny droplets likely to be ejected from the toilet bowl into the air. A similar model was used recently to simulate the movement of aerosol droplets ejected during a human cough, the researchers said. As water pours into the toilet bowl from one side, it strikes the opposite side, creating vortices, the explained. These vortices continue upward into the air above the bowl, carrying droplets to a height of nearly three feet, where they might be inhaled or settle onto surfaces, according to the researchers. These droplets are so small they float in the air for over a minute. A toilet with two inlet ports for water generates an even greater velocity of upward flowing aerosol particles, they said. 

A solution to this deadly problem is to simply close the lid before flushing, since this should decrease aerosol spread, the researchers in the study said. However, in many countries toilets in public restrooms are often without lids, according to the researchers who added that this poses a serious hazard. They also suggest a better toilet design would include a lid that closes automatically before flushing