A new study found that the standard cleaning procedures in retail delis are not enough to wipe out Listeria.

Listeria is a bacterium that infects humans through contaminated food, which can lead to food poisoning or other diseases. According to the U.S. Centers for Disease Control and Prevention (CDC), about 1,600 illnesses and 260 deaths per year are linked to the listeria in the United States. The worst listeria outbreak in the country was in 2011, wherein 147 illnesses, 33 deaths, and 1 miscarriage were recorded after eating cantaloupe from a single farm.

However, a study conducted by researchers at the Purdue University warned that one can get listeria by simply ordering food retail delis. They collected samples from 15 delis before and during operating hours to check if the standard cleaning procedures they have are enough to eliminate the bacteria.

The analysis showed that seven percent of the samples were positive of Listeria monocytogenes bacteria even before the delis open. The rate increased to 10 percent during operation. Samples were randomly collected within six months.

"This is a public health challenge," said Haley Oliver, study leader and an assistant professor of food science, in a university news release. "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."

Most of the positive samples were collected from floors, drains, and squeegees, but the bacteria can be transferred unintentionally from these surfaces to the food.

The researchers believe that the findings of their study can be useful in improving the sanitation cleaning procedures in delis. It is also recommended that people with vulnerable immune systems should buy prepackaged deli meats or heat the ready-to-eat meals to 165 degrees to cut their risks of Listeria infection.

The study was published in the Journal of Food Protection.