Hold The Listeria: Your Deli Sandwich Could Be Crawling With Bacteria

PHILADELPHIA (CBS) – From cheesesteaks to roast pork, Philly has informally been crowned the sandwich capital of the United States.

But a new study might have you thinking twice before ordering from your favorite deli.

Purdue University recently conducted a study on 30 delis inside national supermarket chains in three states.

The researchers apparently swabbed surfaces that often come into contact with deli meats, like the slicer and countertops, as well as areas that don't typically touch food, for the presence of L. monocytogenes and other Listeria species.

While 30% of the delis studied never tested positive for the bacteria, some delis did test positive in 35% of the samples collected. Futhermore, the researchers tested 442 of the L. monocytogenes isolates collected from the delis to see how virulent they were, or how likely it is that they could cause disease. Turns out less than 3% of had a lower potential for virulence.

"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," says study leader and assistant professor of food sciences Haley Oliver.

Though researchers note that many of the samples that came back positive were from areas of the delis that don't typically come into close contact with food, they also say that bacteria can be transferred unintentionally from those spots to your sandwich.

What's interesting to note is that while manufacturing has "a zero-tolerance policy for Listeria," retailers don't have the same restrictions. Purdue University says that up to 83% of listeriosis cases are linked to deli meats can be attributed to the retail level rather than to manufacturing.

The takeaway? Scientists recommend customers with vulnerable immune systems buy pre-packaged deli meats or heat deli meat to at least 165 degrees.

For more on the study, click here.