Clinical Features/Signs and Symptoms

Listeriosis is a life-threatening infection caused by eating food contaminated with the bacterium (germ) Listeria monocytogenes. The disease primarily affects pregnant women and their newborns, older adults, and people with immune systems weakened by cancer, cancer treatments, or other serious conditions (like diabetes, kidney failure, liver disease, and HIV). Rarely, people without these risk factors are affected.

A person with listeriosis usually has fever and muscle aches, sometimes preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has invasive infection, meaning the bacteria spread from their intestines to the blood, causing bloodstream infection, or to the central nervous system, causing meningitis. Although people can sometimes develop listeriosis up to 2 months after eating contaminated food, symptoms usually start within several days. Listeriosis is treated with antibiotics.

The symptoms vary with the infected person:

• Higher-risk people other than pregnant women: Symptoms can include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions.
• Pregnant women: Pregnant women typically experience only fever, and other non-specific symptoms like chills and headache. However, infection during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
• Healthy people. Healthy people rarely develop invasive listeriosis. However, people exposed to a very large dose of Listeria bacteria can develop a non-invasive illness (meaning the bacteria do not spread into their bloodstream or other sites) with diarrhea and fever.

If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for people at higher risk for listeriosis.