Each time you flush the toilet, a plume of tiny droplets of water and faeces are thrown up to 1.5m into the air. Carried with this aerosol-like spray can be bacteria viruses such as those that cause flu, Covid-19 and the winter vomiting bug norovirus https://www.bbc.com/future/article/20251017-why-you-might-want-to-clean-your-toothbrush-more "If you happen to keep your toothbrush close by, then the contents of your toilet bowl could well end up settling on to the bristles you later put into your mouth. There is more risk of directly inhaling infectious microorganisms at the time of flushing, but you might want to think twice about leaving the toilet seat up before you flush in future"