Listeriosis is infection caused by the gram-positive bacteria Listeria monocytogenes.
Listeria monocytogenes resides in the intestine of many animals worldwide. Most cases of listeriosis result from eating contaminated food. The bacteria grow in food at refrigerator temperatures and survive in the freezer. Pasteurization of dairy products destroys the bacteria unless many bacteria are present. Adequate cooking or reheating of food kills the bacteria. However, they can reside in food-filled cracks and inaccessible areas in commercial food preparation facilities and recontaminate food. If the food requires no further cooking once purchased, the bacteria that remain are consumed with the food. They can grow in a refrigerated, packaged, ready-to-eat product without changing the food's taste or smell. Foods involved in previous outbreaks of listerosis include soft cheeses (such as Latin American white cheeses, feta, Brie, and Camembert), delicatessen salads (such as cole slaw), unpasteurized milk, cold cuts, turkey franks, other hot dogs, shrimp, and undercooked chicken.
The bacteria sometimes enter the bloodstream from the intestine and spread, causing invasive listeriosis. Bacteria may spread to the space within the tissues covering the brain and spinal cord (causing meningitis), the eyes, heart valves (causing endocarditis), or, in pregnant women, the uterus. Collections of pus (abscesses) may form in the brain and spinal cord. In the United States, invasive listeriosis develops in only about 2,500 people each year but is fatal in 20 to 30%. It is more common among pregnant women, newborns, people aged 60 or older, and people with a weakened immune system, such as those with human immunodeficiency (HIV) infection. About one third of cases occur in pregnant women.
People typically have chills, fever, and muscle aches (resembling the flu), with nausea, vomiting, and diarrhea. Usually, symptoms resolve in 5 to 10 days.
If invasive listeriosis develops, symptoms vary depending on the area infected. If meningitis develops, people have a headache and a stiff neck. They may become confused and lose their balance. If the uterus or placenta is infected in a pregnant woman, spontaneous abortion or stillbirth may result. Or the newborn may have a bloodstream infection (sepsis) or meningitis. About one half of newborns infected near or at the end of the pregnancy die.
A sample of blood is withdrawn. If people have symptoms of meningitis, a spinal tap (lumbar puncture) is done to obtain a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid). The samples are sent to a laboratory to grow (culture) the bacteria. Identifying the bacteria in the sample confirms the diagnosis.
The antibiotic ampicillin or, for people who are allergic to penicillin, trimethoprim-sulfamethoxazole usually cures listeriosis. These antibiotics are given intravenously. If the heart valves are infected, a second antibiotic (such as gentamicin) may be given at the same time.
Eye infections can be treated with erythromycin, given by mouth, or trimethoprim-sulfamethoxazole, given intravenously.
Last full review/revision September 2008 by Matthew E. Levison, MD