Study: Listeria thrives in retail delis

DeliSandwich_blogYour favorite deli sandwich may come with an unexpected side, according to a new study that took thousands of samples at retail delis around the U.S and found some of the highest rates of the foodborne pathogen, Listeria monocytogenes ever recorded.

In healthy individuals, eating food contaminated with Listeria monocytogenes may lead to common food poisoning symptoms such as diarrhea or an upset stomach. However, the bacterium can cause listeriosis, a serious systemic infection, in those with an already compromised immune system including the elderly, infants and children, and pregnant women especially. 

Listeria monocytogenesis most commonly found in ready-to-eat deli meats, and unlike Salmonella and E. coli, it can grow at refrigerator temperatures.

The study indicates that over the course of six months, the research team from Purdue University took more than 4,500 samples from 30 grocery delis of major national retailers. They looked for contamination in three types of surfaces: food-contact surfaces, such as meat slicers; non-food-contact surfaces, such as floors, and potential transfer points, such as handles and knobs.

A recent article describes that the research team found contamination on 4.5% of food-contact surfaces and 14.2% of non-food-contact areas, for an average of 9.5% contamination for all samples. They also found contamination on 3.3% of transfer points.

“Manufacturing has been under scrutiny for quite some time to control for Listeria, but a deli is a much more complicated environment,” Haley Oliver, assistant professor of food science at Purdue University and lead author of the study, said in the article. Oliver went on to explain that it is more difficult to standardize pathogen controls in the open environments of delis, especially where foot traffic and floor plans vary slightly from one location to the next.

Listeria monocytogenes is only estimated to infect about 1,600 people in the U.S. each year, but it kills roughly 260 of them, making it one of the most deadly pathogens found in food.  However, Oliver states in the article that tracking such a Listeria outbreak is no small feat.

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 went on in the article to say that it is very likely that infections occur sporadically from retail deli meat, but not frequently enough for health department investigators to triangulate a source. Also, Listeria infections also have an abnormally wide incubation period, stretching anywhere from three to 70 days, making it even more difficult to identify illness clusters.

However, of the infections that have been connected to deli meats, as much as 80% have come from deli meats sliced at retail groceries, Ernest Julian, chief of the Office of Food Protection at the Rhode Island Department of Health told Food Safety News in another recent article.

Oliver said that deli slicers are most certainly not getting cleaned as often as recommended. It can take 20 or 30 minutes to properly clean a deli slicer, with some companies recommending they be cleaned as often as every four hours.

Next, the research team will examine how well the delis reduced their Listeria rates after following new or revised sanitation procedures. Since the team did find some stores with no prevalence of Listeria during their study, they believe this standard can be achieved.

Neogen is a leader in developing and marketing test kits that provide food safety solutions, including those for Listeria and Listeria monocytogenes. For more information, click here.

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