Listeriosis is a type of food poisoning caused by a bacteria called Listeria monocytogenes. Some foods are more likely to be contaminated with listeria than others. Although listeriosis is rare, some people can die from it. People at risk from listeria are: pregnant women unborn children newborns older people people with weakened immune systems — such as people being treated for cancer Listeria is common in the environment and can contaminate some foods.