Listeriosis is an illness caused by the bacteria Listeria monocytogenes .
Cases generally occur sporadically throughout the year.
Between 1993 and 1997, an average of 10 cases per year were reported in Oklahoma. Anyone can get listeriosis. Those most at risk for developing severe disease symptoms are newborn infants, the elderly, persons having a suppressed immune system, persons with chronic illnesses such as cirrhosis of the liver, or diabetes, and pregnant women. Children, and adults to age 40, are generally resistant to the bacteria. After age 40, resistance gradually decreases.