Actually, the incubation period can also be the case if it comes to 'stomach bugs'. It could be something you ate couple of days ago that is giving you hard time. It alway perplexes me how people immediately associate their stomach or intestine discomfort (and I am talking about something a bit more serious like diarrhea or vomiting) with the last meal they ate. Which also normally leads people to ban the restaurant, take away they ate from immediately.

How many times it has happened that you at the same thing as other people and you were the only one sick? Plenty, I am sure.