New research finds that 6.8 percent of samples taken in 15 delis before operation began for the day tested positive for Listeria monocytogenes bacteria, which can cause a potentially fatal disease in people with vulnerable immune systems.
In a second sampling phase, 9.5 percent of samples taken in 30 delis during operation over six months tested positive for L. monocytogenes. In 12 delis, the same subtypes of the bacteria cropped up in several of the monthly samplings, which could mean that the bacteria can persist in growth niches over time.
“This is a public health challenge,” says Hayley Oliver, assistant professor of food science at Purdue University. “These data suggest that failure to thoroughly execute cleaning and sanitation protocols is allowing L. monocytogenes to persist in some stores. We can’t in good conscience tell people with weak immune systems that it is safe to eat at the deli.”
In healthy people, eating food contaminated with L. monocytogenes may lead to common food poisoning symptoms such as diarrhea or an upset stomach. But the bacteria can cause listeriosis—a serious systemic infection—in immunocompromised people such as the elderly, infants and children, pregnant women, and people with HIV.
In severe cases, L. monocytogenes can pass through the intestinal membrane and into the bloodstream or cross the blood-brain barrier. The bacteria can also cross the placental barrier in pregnant women, which can trigger abortion.
‘Wild West’ of Lunchmeat
Ready-to-eat deli meats are the food most associated with L. monocytogenes, which, unlike Salmonella and E. coli, can grow at refrigerator temperatures.
Stringent control measures and inspections have tamped down the presence of L. monocytogenes at meat processing plants, but there are no regulations specific to Listeria for retail delis. Recent risk assessments suggest that up to 83 percent of listeriosis cases linked to deli meats are attributable to products contaminated at retail.
