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INTRODUCTION

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Listeria monocytogenes is a saprophytic organism (found in multiple environments including water, soil, and decaying vegetation) and a foodborne pathogen that causes disease primarily in pregnant women, the elderly, immunocompromised hosts, and neonates. It has a worldwide distribution and is acquired relatively frequently in developed countries due to consumption of refrigerated, contaminated, ready-to-eat food, mostly dairy products and cold cuts. Listeriosis is a zoonosis of many animal species that can directly transmit infection to humans. In humans, it causes epidemic and sometimes sporadic outbreaks of febrile gastroenteritis.

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PATHOGENESIS AND EPIDEMIOLOGY

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L monocytogenes is a facultatively anaerobic, gram-positive, motile bacillus, often observed in clinical specimens as gram-variable. Systemic infection results from passage of the organism across the intestinal mucosal barrier by endocytosis, coupled with its ability to evade immune surveillance by cell-to-cell spread; deficiencies in T-cell immunity such as in pregnancy and immunosuppression increase the risk of listeriosis. Extraintestinal disease results from hematogenous dissemination with particular predilection for central nervous system and placental infections. The mode of acquisition in neonates is mainly by vertical transplacental transmission or through the birth canal in parturition.

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In 2009 to 2011, there were 1651 reported cases of Listeria illness in the United States, with an annual incidence of 0.29 cases per 100,000 population and a case fatality rate of 21%. Adults over 65 years of age accounted for 58% of the cases and pregnant women for 14% of the cases. The majority of nonpregnant patients younger than 65 years of age (74%) were immunocompromised.

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CLINICAL MANIFESTATIONS

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Bacteremic illness in a pregnant woman presents with a nonspecific febrile illness (eg, flulike or gastrointestinal symptoms) and may progress to amnionitis, with brown staining of amniotic fluid, preterm labor, or septic abortion in 3 to 7 days. Perinatal listeriosis results in neonatal death or stillbirth in 22% of the cases. Neonatal listeriosis has both early- and late-onset presentations. Neonates with early-onset listeriosis, typically acquired in utero through transplacental transmission, usually present at 1 to 2 days of age with sepsis. Respiratory distress, pneumonia, and, rarely, meningitis and granulomatosis infantisepticum also are described. The latter is manifested by diffuse granulomas in the liver, skin, and placenta as well as other organs in addition to a papular rash on the skin. The fatality rate for early-onset listeriosis is 14% to 56%. Late-onset listeriosis of the neonate can result from infection acquired during passage through the birth canal or through environmental sources or through healthcare-associated acquisition. Late-onset disease typically presents at 2 weeks of age (range, 8–30 days), most commonly as meningitis. The fatality rate for late-onset neonatal listeriosis is approximately 25%.

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After the neonatal period, invasive listeriosis most commonly presents in an immunocompromised or elderly patient as bacteremia without a source or as meningitis (30–55% of cases), leading to neurologic sequelae in 30%. Other forms of central nervous system infection include meningoencephalitis, ...

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