When I took over the fish room at a pet store with 80some freshwater tanks (all in deplorable condition, most without even a heater or filter, GROSS..) and 4 saltwater sytems I was concerned about pathogens and bacteria, especially since I was using razors daily to remove black brush algea that covered about half of them and I have birds that scratch my hands and arms up pretty good.
I spent up to 8 hours a day working in those tanks rinsing my hands in between tanks but never really washing or drying them until I was done or going to eat.
I did that for a year, worked in 2 more stores doing the same thing (with far cleaner tanks, thank god) over the next 2 years, plus I have my own fish.
Never had any serious problems. Some irritation working with the coral tanks, especially since I was warring to erradicate (control really) the aptaisia infestation in those first 4 salt systems. If I did a lot of work in the coral system, moving the live rock and touching some of the corals, I got tons of tiny scratches and a rash but it always went away within a day.
Had more problems getting zapped by the crappy wiring and damaged powerheads than anything..