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Listeria monocytogenes is
a food-borne pathogen that causes disease primarily in neonates,
pregnant women, the elderly, and the immunocompromised host.1 It
is worldwide in 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.2 Listeriosis
is a zoonosis of many animal species. In humans, it causes epidemic
and sometimes sporadic outbreaks of febrile gastroenteritis.3 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.4,5 Extraintestinal disease
results from hematogenous dissemination with particular predilection
for central nervous system and placental infections.
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Neonates are typically infected transplacentally or by birth
through an infected birth canal.
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Clinical Manifestations
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The bacteremic illness in the mother presents with a nonspecific
illness (flulike or gastrointestinal symptoms) and may progress
to amnionitis, preterm labor, or septic abortion in 3 to 7 days.6 Perinatal
listeriosis results in neonatal death or stillbirth in 22% of
the cases. Neonatal listeriosis has an early and a late onset presentation.
Neonates with early onset disease usually present at 1 to 2 days
of age, are born prematurely, and typically exhibit a septiclike
picture, although respiratory distress, pneumonia, and, rarely,
meningitis and granulomatosis infantisepticum are described. The
latter is manifested by diffuse granulomas in the liver, skin, and
placenta as well as other organs. Late onset disease typically presents
at 2 weeks of age, most commonly as meningitis. The case fatality
rate in neonates is 20% to 30%.4 Population-based
studies show that 88% of listeriosis in children younger
than 5 years occurs before 1 year of age, half of which presents
on the first day of life.7In 2006, 58 of 884 cases
reported in the United States were in children younger than 5 years, whereas
the majority of cases occurred in the elderly.8 After
the neonatal period, invasive listeriosis most commonly presents
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,
cerebritis, brainstem or spinal cord abscesses, and brainstem involvement
(rhombencephalitis).
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Diagnosis and Treatment
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The diagnosis is established by positive blood or cerebrospinal
fluid (CSF) cultures. Peripheral leukocytosis is common. In meningitis, the
CSF is usually purulent with polymorphonuclear cell predominance,
an elevated protein level, and often a low or normal glucose.4,9 Rarely,
the CSF is devoid of inflammatory cells.10 The
CSF Gram stain is positive in only 40%. Concomitant blood
cultures are positive in about two thirds of the patients. Real-time polymerase
chain reaction on blood specimens may speed up the detection of
neonatal sepsis, including that secondary to L monocytogenes.11
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