I've been to the Royal Decameron in El Salvador 3 times, never been sick. On the plane I bring Lysol disinfecting wipes in a ziploc bag and wipe the tray table and metal parts of armrest and seatbelt with them, and use my hand sanitizer before eating.
When I first arrive at the resort and check into the room, I bring Lysol Spray and spray all surfaces of the room and wait 20-30 minutes before wiping it off. Surfaces such as door knobs, light switches, and bathroom stuff, as I figure when the clean the rooms, they aren't really disinfecting, so maybe that is how illness gets passed to the next guest in the room.
I also never use the glasses provided in the rooms for water, as I wonder if the maids use the same cloth to clean those glasses as they used in other rooms, so I always bring a clean plastic glass back from the bar each night to brush my teeth.
Also, I use my hand sanitizer after using their public restrooms, and before eating.
I don't know if this is why I and my husband have never been sick, but it doesn't hurt to try!