In your bathroom, do you store your toothbrush inside the cabinet or you have them out on the shelf or vanity counter? Have you ever thought about the fact that if those toothbrushes are on the shelf or counter and the proximity of the counter and the toilet is close enough, airborne bacteria can spread?
I’ve been aware of that. And yes, when you flush the toilet some germs can be sent out into the air. That’s why, as an added measure whenever I flush the toilet, I ensure that the lid of the toilet is always closed.
If it is unavoidable that your toothbrush is on a shelf or on the sink, and it’s close to the toilet, covering the bristles is a good idea. Apart from that, ensure that each individual toothbrushes don’t touch each other. Periodontal disease and infections can be passed on this way (from one toothbrush to another), that’s why.