ASSESSMENT OF ALIMENTARY EXPOSURE TO LISTERIA-MONOCYTOGENES

Survey data on the frequency of foodborne occurrence and dietary expos ure to Listeria monocytogenes were used to estimate the mininmal mean per person annual rate of exposure in the United States during the lat e 1980s. The estimate was restricted to ready-to-eat (RTE) foods becau se proper cooking was assumed to be listericidal. The mean amount of e ach food type per L. monocytogenes occurrence was calculated in about 100 sources, and dietary intake data were used to calculate the mean n umber of occurrences of L. monocytogenes consumption per person per ye ar. The mean number of occurrences-consumed annually per person was de termined to be 10 to 100 for RTE food values of 2 to 20% of the total dietary intake, respectively. The frequency of foodborne listeriosis ( approximate to 10(-5)) was consistent with the estimated exposure rate only if the susceptible population was unexpectedly small or extremel y high doses were necessary for;infection. Because little evidence is available to support a high rate of unreported non-severe infections, this study was concerned only with severe listeriosis cases. Published frequencies of L. monocytogenes concentrations in food were used to c onvert occurrences to colony forming units (CFU). Low L. monocytogenes concentrations (approximate to 1 CFU/g) were too frequent to be respo nsible for listeriosis in susceptible subjects, would have caused list eriosis only with extremely low probability in a one-cell threshold in fection model. The probability of exposure to a higher dose (greater t han or equal to 10(3) CFU) was large enough to account for the observe d rate of listeriosis.