Contaminated foods and beverages sicken an estimated 48 million Americans each year. The five bugs most likely to cause an outbreak: Norovirus, Salmonella, Clostridium perfringens, E. coli, and Campylobacter. Together, they accounted for roughly 9 out of 10 illnesses from outbreaks from 2011 to 2015. Listeria monocytogenes isn’t in the top five, but it kills more people than most of the others. Here’s what you need to know about the usual suspects—especially if you’re pregnant, under age 5, or 65 or older, or you have a weakened immune system.