MAY 16–WASHINGTON, DC–Only a small fraction of all Listeria-contaminated foods contain enough of the pathogen to cause illness, according to a pair of studies on Listeria monocytogenes in ready-to-eat (RTE) foods and associated illness rates. Researchers concluded that prevention efforts should focus on limiting the concentration of Listeria in selected foods, rather than the current policy of “zero tolerance,” that requires elimination of the the pathogen from all RTE foods.

The studies by researchers with the National Food Processors Association (NFPA) involved the collection and analysis of thousands of samples of RTE foods in Maryland and California over a two-year period, followed by a comparison of the data on listeria incidence with the incidence of listeriosis in the same areas and same time frame.

Investigators found Listeria in about 577 of more than 31,705 food samples analyzed (1.82 percent), but only 21 of the samples contained more than 100 colony-forming units (about 100 organisms) per gram. The prevalence rates ranged from 4.7 percent for seafood salads to 0.89 percent for sliced luncheon meats, rates “considerably lower than expected,” the researchers said.