The human infectious dose of Listeria monocytogenes
1991
Extensive surveillance by the regulatory agencies and the foods industry has documented that a wide variety of foods may sometimes be contaminated by Listeria monocytogenes. On the other hand, epidemiological investigations have revealed few cases of sporadic listeriosis. Therefore, it is an unusual event for a L. monocytogenes-contaminated food to cause human illness. The infectious dose of a foodborne pathogen depends on many variables including the condition of the host, the virulence and infectivity of the pathogen, the type and amount of foods consumed, the concentration of the pathogen in the food and the number of repetitive challenges (Blaser and Newman, 1982). Most persons who become infected with L. monocytogenes are predisposed to infection because of a disruption in their T cell-mediated immunity (Lorber, 1990). Common predisposing factors leading to the immunocompromised state are: Age- The highest incidence is in neonates and those over 60 year of age. Malignancy- Cancer has been a major risk factor in foodborne outbreaks and sporadic cases. Immunosuppression- Corticosteroids are the immunosuppressive agents most frequently associated with listerial infections. Pregnancy- Pregnant women are particularly prone to listerial infections. Other risk factors that have been associated with listeriosis include: (1) splenectomy or dysfunctional spleen; (2) antacids and cimetidine which neutralize gastric acidity, and; (3) liver disease, particularly cirrhosis. Because of the few detected outbreaks of foodborne listeriosis, little is known about the infectious dose either for healthy or immunocompromised humans.
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