The Food and Drug Administration has begun traceback efforts related to a multi-state outbreak of infections from Listeria monocytogenes.

The source of the outbreak continues to be listed as unknown by the FDA even though it has begun product traceback.

So, top contenders? Leafy Greens? Cheese? Deli Meat? Enoki Mushrooms – again?

According to the Centers for Disease Control and Prevention, there have been 11 people infected across 10 states. Ten of the patients have been so sick that they had to be admitted to hospitals. No deaths have been reported.

The outbreak is long-running with patients having been identified from July 2018 through January this year, according to the CDC. The patients range in age from 47 to 88 years old, with a median age of 73. One-fourth of the patients are female.

Public health officials are continuing to interview patients to find out what foods they ate in the weeks before becoming sick. It can take from several days up to more than two months for symptoms of Listeria infection to develop.

The patients have been identified and linked using whole genome sequencing, which provides DNA fingerprints of the bacteria. The patients’ samples have the same genetic signatures, which shows they are all part of a single outbreak.

The sick people live across the country, suggesting nationally distributed food. The patients live in Washington, California, Colorado, South Dakota, Missouri, Arkansas, Michigan, New York, Pennsylvania, and North Carolina.