There are all sorts of pathogens that can bounce from human to aquarium and vice versa.
Overall the main advice is to not worry too much about it, but fish tb can be very unpleasant. That would be the one to avoid open wounds or even wear gloves when dealing with hands in tanks, but I'm not sure, apart from one person, that I know anyone that bothers.
Generally, if cultured, aquariums contain all sorts of staphylococci and psuedomonas type bugs that can in theory transmit to humans, but there are far more worrying things that you can catch from other places. As for viruses like colds, I'm not sure that there are any that are relevant.
You're more likely to be injured by a coral sting, fish bite or spine, or something sharp on the decor damaging you.