Another possible consideration is cold... if your husband isn't keeping himself warm enough on a dive then potentially it may have some impact on his immune system and his ability to resist infection from another source.
Personally, I think this tends to be influence by general stress as well - it's a bit like why you always get a cold when you go on vacation.
Personally, I think this tends to be influence by general stress as well - it's a bit like why you always get a cold when you go on vacation.