Looks like about 200 people on Ovation have had a rather 'difficult' cruise.
https://au.news.yahoo.com/a/38156826/gastro-hits-hobart-docked-cruise-ship/
I still maintain that cruise ships are cleaner than 99.9% of peoples homes and of course I've never seen so many signs or people reminding you to wash your hands as I have on cruise ship.
Most of them are medical grade and not sold the general public but two are: Clorox Healthcare Hydrogen Peroxide wipes and Oxivir TB wipes. Both kill viruses. Those are the two that I know. Maybe others know of other options. I know @twangster has ones too.
I don't snorkel but friends of ours that do always bring their own equipment. I think that is just cause they prefer it. But yes, anything that goes on your head you think of head lice! I am "that parent", my kids have a gym bag f