Norovirus. It might not have been the food, it is passed on as droplets in the air, via hand touch and items passed from hand to hand, use of toilets, its on doors and doorhandles. it is particularly easy to catch when you are among strangers as you are more likely to be resistant to strains carried by people who you live with or meet often. This (and low resistance to any kind of infection) is why it rips through hospitals. Every single time i have had it, it has been after I have been to an event where there were crowds of strangers, and I am obsessive about hygiene.