Incidence in 2004–2005 was 2.5–3 cases per million population a year in the USA, where pregnant women accounted for 30% of all cases. Of all nonperinatal infections, 70% occur in immunocompromised patients. Incidence in the USA has been falling since the 1990s, in contrast to Europe where changes in eating habits have led to an increase during the same time. In Sweden, it has stabilized at around 5 cases per annum per million population, with pregnant women typically accounting for 1–2 of some 40 total yearly cases.
There are four distinct clinical syndromes:
- Infection in pregnancy: ''Listeria'' can proliferate asymptomatically in the vagina and uterus. If the mother becomes symptomatic, it is usually in the third trimester. Symptoms include fever, myalgias, arthralgias and headache. Miscarriage, stillbirth and preterm labor are complications of this infection. Symptoms last 7-10 days.
- Neonatal infection (granulomatosis infantisepticum): There are two forms. One, an early-onset sepsis, with ''Listeria'' acquired in utero, results in premature birth. ''Listeria'' can be isolated in the placenta, blood, meconium, nose, ears, and throat. Another, late-onset meningitis is acquired through vaginal transmission, although it also has been reported with caesarean deliveries.
- Central nervous system (CNS) infection: ''Listeria'' has a predilection for the brain parenchyma, especially the brain stem, and the meninges. It can cause cranial nerve palsies, encephalitis, meningitis, meningoencephalitis and abscesses. Mental status changes are common. Seizures occur in at least 25% of patients.
- Gastroenteritis: ''L monocytogenes'' can produce food-borne diarrheal disease, which typically is noninvasive. The median incubation period is 21 days, with diarrhea lasting anywhere from 1–3 days. Patients present with fever, muscle aches, gastrointestinal nausea or diarrhea, headache, stiff neck, confusion, loss of balance, or convulsions.
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