Not everyone who is infected with listeria will develop listeriosis. Infants, people older than 50 years old (and especially over 65), or people with an impaired or weakened immune system are most likely to be affected. Symptoms of the disease may appear suddenly, as soon as 1 day after or up to 90 days after eating food contaminated with listeria.
Generally, milder forms of listeriosis will cause symptoms much sooner than more serious forms of the disease.
Symptoms of listeriosis include:
- mild flu-like illness (e.g., chills, fatigue, muscle and joint pain)
- persistent fever
Rarely, very severe forms such as meningoencephalitis (an infection of the brain and the surrounding tissues) or bacteremia (where the bacteria are present in the blood) may follow.
Listeriosis can be particularly harmful during pregnancy. A mother who is infected during the first 3 months of pregnancy may miscarry. Acute illness, premature birth, and stillbirth are possible if the mother is infected later in pregnancy. Newborns may also have low birth weight, meningitis, or overwhelming sepsis.