"Deli meats (cold cuts, lunch meats, hot dogs, and pâtés sold at the deli) and cheeses are known sources of Listeria illnesses," the CDC said. "This is because Listeria can easily spread among food on deli countertops, deli slicers, surfaces, and hands.
"Listeria is a hardy germ that can be difficult to fully remove once it is in the deli. It can survive and grow at cold temperatures in the refrigerator."
The CDC said that it's been difficult for investigators to identify a single food as the source of the outbreak, but that a contaminated food likely introduced the outbreak strain of Listeria into delis in multiple states.
A total of 16 illnesses in six states have been reported in connection to the outbreak, with seven in New York. For a look at cases by state, check this CDC map here.
"The true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses," said the CDC. "This is because some people recover without medical care and are not tested for Listeria."
The CDC first reported the outbreak on Wednesday, Nov. 9.
"Listeria is especially harmful if you are pregnant, 65 years or older, or have a weakened immune system," according to the CDC.
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