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article imageRetail delis show persistent high rate of Listeria contamination

By Karen Graham     Feb 16, 2015 in Food
The rates of Listeria monocytogenes in retail food delis indicates that standard cleaning procedures are not enough to eradicate the potentially dangerous bacteria, according to a new study by researchers at Purdue University.
Listeria monocytogenes (LM) is a bacterium found in moist environments, soil and in decaying vegetation. L. monocytogenes can also grow in cool temperatures (as low as 34˚ F. or 1°C), such as in a refrigerator. Because of its growth and survival characteristics, it is known as a harborage organism, meaning it can create niches, growing to great numbers in the environment.
According to the Centers for Disease Control and Prevention (CDC), L.monocytogenes is responsible for about 1,600 infections in the U.S. every year, resulting in 1,500 hospitalizations, and 260 deaths. While it may appear to be rare, it has a very high fatality rate. It primarily affects older adults, pregnant women, newborns, and those people with weakened immune systems. This is one reason why obstetricians tell pregnant women to heat deli meats before eating them.
Because LM can cross-contaminate foods and food-contact surfaces, improper handling, improper heating and cooling and poor employee practices can all play a role in spreading or transferring LM to meat and poultry products at the retail level. Purdue's study involved 30 delis in national supermarket chains in three states. Researchers swapped surfaces that come into frequent contact with food, such as meat slicers and counters, as well as surfaces that usually do not have contact with foods.
The research team found that 30 percent of the delis never tested positive for the pathogen while some delis tested positive for 35 percent of the samples over a period of six months. Lead author Haley Oliver, assistant professor of food science at Purdue University, told Food Safety News that while manufacturers are required to have strict controls for listeria, retail establishments have no such requirements.
"Manufacturing has been under scrutiny for quite some time to control for Listeria, but a deli is a much more complicated environment," Oliver said. She explained that it is more difficult to have standardized pathogen controls in the open, and often varied floor designs of the retail deli. She also suspects that socio-economic factors might play a role in compliance to sanitation rules because for some deli workers, the job is low-paying, and one with a high turn-over rate, so there is often little training in controlling something like Listeria.
Over a period of six-months, 4,500 samples were taken at the 30 delis. They looked for contamination on three types of surfaces, food-contact surfaces such as meat slicers, non-contact surfaces such as floors, and transfer points such as door knobs and handles. Contamination by LM was found on "4.5 percent of food-contact surfaces and 14.2 percent of non-food-contact areas, for an average of 9.5 percent contamination for all samples," according to the researchers.
"The prevalence of L. monocytogenes is higher than we expected in a significant percentage of delis, and the bacteria is persisting in these delis over time," Oliver said. The rates of contamination were alarming to Oliver, who said pregnant women and those with weakened immune systems should be warned about eating cold deli meats.
We might wonder why there are not more cases of Listeria being reported as coming from delis. Oliver says there is a reason why we don't hear much about this. “Listeria is a ‘perfect storm’ disease,” Oliver said. “Getting enough cases to fall ill at the same time at one deli and then managing to trace them all back to the specific grocery store is extremely difficult." Oliver says Listeria has an extremely long incubation period, from three days to as long as 70 days.
Inside Stein s Deli  restaurant and delicatessen on Magazine Street  Uptown New Orleans. Would you b...
Inside Stein's Deli, restaurant and delicatessen on Magazine Street, Uptown New Orleans. Would you buy cold cuts from here?
Infrogmation of New Orleans
Ernest Julian is chief of the Office of Food Protection at the Rhode Island Department of Health. In speaking to Food Safety News last June, Julian said, "Of the infections that have been connected to deli meats, as much as 80 percent have come from deli meats sliced at retail groceries."
Of the original 30 store delis in the study, eight had what the team considered a "high level" of LM contamination while other stores had no contamination. “We had stores with no positive samples, which tells us that it can be achieved,” she said. “That’s our takeaway message.”
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