Listeria monocytogenes has been recognized as a human pathogen
for 60 years, but food was not thought to be a vehicle of
transmission until recently. In the United States, an estimated
2,000 persons become seriously ill with listeriosis each year.
Of these, 500 die. Pregnant women, newborns, and adults with
weakened immune systems are primarily at risk. About one-third
of Listeria monocytogenes cases occur during pregnancy. Listeria
monocytogenes is found in soil and water. Vegetables can become
contaminated from the soil or from manure used as fertilizer.
Animals can carry the bacteria without appearing ill and can
contaminate foods of animal origin such as meats and dairy
products. The bacteria can be found in a variety of raw foods,
such as uncooked meats and vegetables, as well as in processed
foods that become contaminated after processing, such as soft
cheeses and cold cuts at the deli counter. Unpasteurized (raw)
milk or foods made from unpasteurized milk may contain the
bacteria. Symptoms vary and dep