Wash your hands often - Lot's of issues arise from putting your fingers in/near your mouth. In long established 5 star hotels you can pretty much anything (as staff is typically very well trained in food hygiene) but be careful with 4 and newly opened 5 stars.
Eat yogurt.
When very sick visit a pharmacy or doctor immediately. With the right antibiotic you can be over it in about 24 hours - without it can take 5-7 days of agony.