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FRIDAY, July 23 (HealthDayNews) -- Food retailers and food-processing plants might try to maintain a clean environment, but new research has found that strains of the deadly Listeria monocytogenes pathogen can persist for up to a year or longer.

Listeria can cause listeriosis, a disease that primarily affects pregnant women, newborns, and adults with weakened immune systems. Each year some 2,500 people are infected in the United States, of whom a fifth die.

The bacterium was found directly on food in 47 of 50 retail food stores examined by Cornell University food scientists. When the 50 stores were re-inspected weeks, months, or even a year later, about 34 percent had persistence of the same strains of Listeria.

Listeria also was found in seven food-processing plants, and three had persistent strains of the bacterium.

"This is disturbing because this points the finger at retail stores and some processors as a continuing source of food contamination," said doctoral candidate Brian D. Sauders, who worked on the study published in the July issue of the Journal of Food Protection.

The foods in which Listeria was found included ready-to-eat delicatessen foods such as ham, beef bologna, chicken, pastrami, roast beef, and smoked fish. It also was found in hummus, imitation crab, cheeses, and in foods requiring cooking before consumption, like hot dogs and raw beef.

Listeria can be eliminated through pasteurization or cooking.

More information

The U.S. Centers for Disease Control and Prevention has more about listeriosis.

(SOURCES: Cornell University, news release, July 16, 2004)

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