Listeria in Poultry Processing

The main route of transmission is oral, through ingestion of contaminated foods. Soil or manure used as fertilizer can contaminate vegetables, and food animals can be asymptomatic carriers. The infectious dose is unknown.

In recent years, the major outbreaks of listeriosis have been associated with ready-to-eat (RTE) foods, such as hot dogs, cold cuts and luncheon meats. Fermented or dry sausage and other deli-style meat and poultry products have also been incriminated in the production of listeriosis.

Most L. monocytogenes strains can cause disease. However, there is a large range of virulence among strains, with some being avirulent and others highly virulent. The virulence in L. monocytogenes appears to be linked to several genes, and we do not have a complete understanding of why some strains are more virulent than others. Yet, only three serotypes have accounted for more than 90% of all cases of human listeriosis.

The Food and Drug Administration (FDA) in conjunction with the Food Safety and Inspection Service of the U. S. Department of Agriculture (FSIS, USDA) and the Centers for Disease Control and Prevention (CDC) calculated the relative risk to public health from foodborne L. monocytogenes among selected categories of RTE foods. The calculation was done on outbreaks from 1970 to 2000. When ranked by number of outbreaks of listeriosis, dairy products ranked highest, followed by meat products, then seafood and finally produce. When the total numbers of cases of listeriosis in the outbreaks cases were ranked, meat products were first and dairy products were second. Meat and dairy products were implicated in more than 90% of the cases of listeriosis. Dairy and meat products were also implicated in three outbreaks with multiple food vehicles. Between 1990 and 2000, the FSIS USDA conducted a microbiology testing in 1,800 federally inspected establishments. From that testing, the cumulative prevalence of L. monocytogenes in RTE meat and poultry products was: 4.47% for sliced ham and luncheon meats; 2.95% for cooked beef, roast beef and corned beef; 2.83% for salads/spreads/pâtés; 2.67% for fermented sausages; 1.97% for cooked, uncured poultry products; 1.09% for large-diameter cooked sausages; 2.97% for small-diameter cooked sausages; and 0.58% for jerky. In other parts of the world, and for a variety of foods, the prevalence of L. monocytogenes varies from 1 to 10% or more. Listeria monocytogenes has the ability to grow at refrigerator temperatures, a feature that makes these bacteria extremely dangerous in certain foods where growth is allowed to occur. The annual incidence of listeriosis has steadily decreased by 44% between 1989 and 1993. However, outbreaks have continued to occur as recently as 2002, in which an outbreak traced to consumption of contaminated turkey meat produced 54 illnesses, eight deaths, and three fetal deaths in nine states.

• Isolated human cases, where it is difficult to identify a specific food as the source of contamination due to the long incubation period of this disease.
• Outbreaks involving a single lot of contaminated food, where mistakes in food handling lead to the contamination of a food and an opportunity for growth before that food is consumed.
• Outbreaks involving multiple lots of food over days or months of production due to a highly virulent strain established in the food processing environment. A “niche” is usually involved in these cases. A niche is a place or site inside the manufacturing environment where L. monocytogenes becomes established and multiplies. Any crack on a wall or space in the equipment that is difficult or impossible to reach and sanitize is an ideal area for the development of a niche. From a niche, L. monocytogenes spreads and contaminates product contact surfaces and the food.

• Prevent the establishment of L. monocytogenes in niches or other sites that can lead to the contamination of RTE foods.
• Implement an environmental sampling program to assess potential exposure of RTE foods to L. monocytogenes.
• Perform periodic assessments of the results from environmental samples to detect early trends or problems. These assessments should be done in the short- and long-term.
• Emphasize cleaning and sanitation in areas where environmental samples turned out positive. Follow-up with sampling of those problem areas to assure that the possible contamination sources have been removed.

• Wash all eating utensils with hot, soapy water after they have come in contact with contaminated foods.
• Cook thoroughly all foods from animal origin, such as beef and poultry.
• Do not consume unpasteurized milk or foods made from unpasteurized milk.
• Avoid cross-contamination of the food products by keeping raw meat, poultry, and seafood separated from vegetables, fruits, breads, and other RTE foods.
• Reheat luncheon meats, cold cuts, and deli-style meats until they are steaming hot if you are within the category of people at high risk for listeriosis.

 Listeriosis appears predominantly in pregnant women and the immunocompromised. L. monocytogenes can survive and multiply in the processing environment and under refrigeration temperatures; therefore, RTE food products that become contaminated would be of high risk to the consumer. Although not all L. monocytogenes strains are pathogenic, the industry and government continue to treat all L. monocytogenes strains as potentially pathogenic. Finally, prevention and control during processing must be continuously emphasized in processing environments that make food products considered high-risk for the transmission of listeriosis.