Some people may notice a mild flu-like illness with fever. Persons identified above as most at risk, may develop severe disease. There is special concern for listeriosis in pregnant women because they can transfer the bacteria to the fetus. Spontaneous abortion may occur as a result. Listeria is commonly found in soil, vegetation, water and mud.
Listeria also infects domestic and wild animals, livestock and fowl.
Most cases of listeriosis result from eating contaminated food products. Unlike most other bacteria, Listeria multiplies at refrigerator temperatures. Listeria can also grow on soft cheeses during their ripening period. The average time period between exposure and symptoms is thought to be 3 weeks, but can range from 3 to 70 days. Persons who are ill should see their health care provider.