Listeria found in 10% of samples of food contact surfaces in US delis

Academics have warned of the danger of listeria poisoning after a study of deli counters in supermarkets located in three US states.

Haley Oliver, who headed the team based at Indiana’s Purdue University, says: ‘The prevalence of listeria monocytogenes is higher than we expected in a significant percentage of delis, and the bacteria is persisting in these delis over time.’

Oliver’s group made repeat visits to 30 delis in three states over the six-month period of the study. At each they took multiple samples to detect for the bacteria. This included testing surfaces and tools, like slicers and chopping counters, which are expected to contact food; and areas that are not, like flooring.

A total of 9.5% of samples showed positive for listeria monocytogenes. The prevalence was higher on those areas not expected to contact food. A number of deli areas gave repeat positive results, indicating that they may be harbouring a community of the bacteria.

Oliver concludes: ‘The prevalence of listeria monocytogenes is higher than we expected in a significant percentage of delis…These data suggest that failure to thoroughly execute cleaning and sanitation protocols is allowing listeria monocytogenes to persist in some stores.’

Commenting on the results published in the Journal of Food Protection on 14 November 2014, Oliver suggested that it should prompt vulnerable groups – like pregnant women and those with compromised immune systems – to not buy deli-prepared meat, but instead rely on pre-packed products.

There are, on average, 1,600 serious cases of listeriosis infection – and 260 deaths – each year in the US, according to the Center for Disease Control.

Oliver continues: ‘We cannot in good conscience tell people with weak immune systems that it is safe to eat at the deli. It is kind of the Wild West. Manufacturing has a zero-tolerance policy for listeria, but that dissipates at the retail level. These numbers would never be acceptable in manufacturing.

‘The reason we have not had a listeriosis outbreak tied to a deli is because it’s a disease with a long incubation time, and it’s difficult to track to a source.’

This article comes from Food Contact World, which provides exclusive news and analysis on developments in digital print trends, markets, and technologies.