How do you know it was something they served?
First I would call some of the other guests and see who got sick....and if none did I would assum that it was either a bug or something you ate somewhere else.
But if you and the rest of the guests got food poisioning....I would tell them.
Linda C

I agree with linda,you do not want to afend anyone.

Of course, if the other guests also fell ill, the hosts probably did as well.

Nope I wouldn't. I don't see what purpose it would serve other than make them feel embarrassed. Now if it happened more than once....

I would not...........

Not unless I was hospitalized. I just wouldn't eat there again.

I wouldnt unless I took really sick IE: hospital or death LOL

I would not. Maybe the food made people sick or maybe there was a virus going around. I would just chuck it up to the flu and move on. Give them the benefit of the doubt. If you feel strongly that you got ill from the food, I guess you could just be busy next time they invited you for dinner...