Ongoing High Incidence and Case-Fatality

borne and cause gastrointestinal disease or invasive syndromes among infected persons (1). Because L. monocytogenes is an intracellular pathogen and because invasive listeriosis is the primary manifestation in diagnosed listeriosis, persons with defi cient cell-mediated immunity are at increased risk for its symptoms, including sepsis and meningitis. In addition, infection during pregnancy can lead to chorioamnionitis and fetal infection that can result in miscarriage and stillbirth even 2 months after the mother is exposed. One study found that 44% of patients with non–pregnancyassociated (NPA) listeriosis in Germany had received immunosuppressive therapy ≤3 months before illness onset and another 28% had a coexistent immunocompromising illness, such as diabetes (2). Testing for bacteria in blood cultures or cerebrospinal fl uid (CSF) is recommended for diagnosis. Listeria is ubiquitous in the environment and can produce biofi lms in the food production environment and thus contaminate ready-to-eat (RTE) products, which are typically consumed raw or without further processing. Listeria species grow during shelf life, even at low temperatures, and multiply to concentration levels that make invasive listeriosis and outbreaks more likely. For these reasons, it is suspected that L. monocytogenes exposure is very common but the disease rare. However, in recent years several large outbreaks have been reported in Germany (3–7).