Nah, it's not quarantined at all. You get off at various stops along the cruise (or at least ours did).

Regardless, I think it's mostly food poisoning from the buffets since I doubt they have very high food safety standards. IIRC most cruise ship staff are also borderline enslaved so it's not like they give much of a shit either.

There are some that take a week or so, but they usually stop in each destination for a day or so and you aren't really on the boat unless you're traveling to the next spot at night.