Listeriosis is a bacterial infection caused by a Gram-positive, motile bacterium, Listeria monocytogenes. Listeriosis occurs primarily in newborn infants, elderly patients, and patients who are immunocompromised. Listeriosis kills at least 1 in 5 persons it infects. Its wide range of temperature tolerance necessitates extra care in food processing and storage. Meat and dairy products must be handled carefully to prevent contamination and growth of the pathogen.