You could be developing an "allergy" to shellfish. Shrimps, oysters and such - lots of people develop it & get nauseous from it.

(I'd like to tell you to try it again, experimentally eat a load of shrimp - but I don't want you to feel bad).

I had it once, I don't think there was anything wrong with the oysters, maybe it was a reaction to stress - ever since oysters don't really appeal to me anymore.

Regular flu viruses are only contracted via your nasal mucosa, and unless someone sneezed on that apple - very unlikely...