Federal officials are investigating a new multi-state outbreak of infections from Listeria monocytogenes bacteria.

A source of the pathogen has not yet been identified, according to the Centers for Disease Control and Prevention. The CDC reports that 11 people across 10 states have been infected. Ten patients have been so sick that they required hospitalization. No deaths have been reported as of Feb. 15.

Patients are spread across the country from coast to coast. States with sick people are Washington, California, Colorado, South Dakota, Missouri, Arkansas, Michigan, New York, Pennsylvania and North Carolina.

The Food and Drug Administration is assisting with the investigation. The agency has not yet been able to begin traceback or sampling efforts because of the unknown source of the pathogen.

Patients began getting sick in July 2018 with the most recent illness onsets in January this year. More people became ill in January 2023 than in the previous time frame.

All of the patients became infected by the same strain of Listeria monocytogenes, meaning their illnesses were caused by the same source, according to DNA testing.

The patients range in age from 47 to 88 years old. Seventy-three percent of the patients are female.

“State and local public health officials are interviewing people to find out what foods they ate in the month before they got sick,” according to the CDC’s outbreak notice.

“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. This is because some people recover without medical care and are not tested for Listeria. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.”

Health care providers and local public health departments are being urged to report all cases of Listeria infections to state and federal authorities so that additional testing can be done to determine whether patients are part of the outbreak.

The CDC is recommending that people take the following steps:

About Listeria infections
Food contaminated with Listeria monocytogenes may not look or smell spoiled but can still cause serious and sometimes life-threatening infections. Anyone who has developed symptoms of Listeria infection should seek medical treatment.

It can take up to 70 days after exposure to Listeria for symptoms of listeriosis to develop.

Symptoms of Listeria infection can include vomiting, nausea, persistent fever, muscle aches, severe headache, and neck stiffness. Specific laboratory tests are required to diagnose Listeria infections, which can mimic other illnesses.

Pregnant women, the elderly, young children, and people such as cancer patients who have weakened immune systems are particularly at risk of serious illnesses, life-threatening infections, and other complications. Although infected pregnant women may experience only mild, flu-like symptoms, their infections can lead to premature delivery, infection of the newborn, or even stillbirth.