Public health officials are investigating an outbreak of infections from Listeria monocytogenes linked to enoki mushrooms. 

Patients live in Michigan and Nevada with one sick person confirmed in each state. Both have been hospitalized and both report eating enoki mushrooms before becoming ill. The most recent illness onset was Nov. 15.

“Investigators are working to identify specific brands of enoki mushrooms that may be linked to these illnesses,” according to an outbreak announcement from the Centers for Disease Control and Prevention.

“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.”

Also, it can take up to 70 days for symptoms to develop, and the CDC says it can take three to four weeks to determine whether a person is part of an outbreak.

The two sick people are 30 and 42 years old, and they are both males. Both sick people reported eating enoki mushrooms or eating at restaurants with menu items containing enoki mushrooms.

Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses. DNA fingerprinting is performed on bacteria using a method called whole genome sequencing (WGS).

WGS showed that bacteria from sick people’s samples are closely related genetically. This suggests that people in this outbreak got sick from the same food.

In November, the Food and Drug Administration found Listeria in a sample of enoki mushrooms that they collected at import, as part of the FDA’s strategy to prevent Listeria outbreaks linked to imported enoki mushrooms  .“These enoki mushrooms were destroyed. The Listeria from this sample is closely related genetically to the Listeria that made the people in this outbreak sick. However, to date, the firm associated with this sample has not been identified as a potential source of enoki mushrooms in this outbreak,” according to the CDC.

“CDC advises people who are pregnant, aged 65 or older, or have a weakened immune system to not eat raw enoki mushrooms. CDC also advises restaurants to not serve raw enoki mushrooms. Cook enoki mushrooms thoroughly to kill any foodborne germs.”

Currently, FDA has issued three import alerts that include enoki mushrooms.

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 eaten any enoki mushrooms and developed symptoms of Listeria infection should seek medical treatment and tell their doctors about the possible Listeria exposure.

Also, anyone who has eaten any enoki mushrooms should monitor themselves for symptoms during the coming weeks because 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.