A: A picture is worth a 1000 words.
TL;DR: Close the lid.
Scientists recently used lasers to measure aerosols (tiny water droplets) coming out of toilets after a flush. They found that a typical commercial toilet generates a strong upward jet of air that rapidly carries these particles up to 5 feet above the bowl.
What does this mean for disease?
This study was done by engineers and only measured the physics of toilet plumes. Toilet bowl water containing feces has been shown to retain pathogen concentrations after dozens of flushes, but how this translates into transmission risk is still an open question.
In theory, these aerosols could cause disease. Smaller particles that remain suspended in air can be inhaled and risk exposure to respiratory diseases like influenza and COVID-19. Larger particles that settle on surfaces can spread those nasty stomach bugs like norovirus through hand (or toothbrush) to mouth contact.
While closing the lid can help a lot, we know many public toilets do not have lids. While engineers are looking into ways to design toilets to reduce the plume, good ventilation and UV disinfection may help in the meantime.
Besides washing hands and keeping your toothbrush covered, toilet plume is also a good reason to consider masking in public restrooms.
Stay safe. Avoid the plume!
Those Nerdy Girls