Ziad M. Shehab
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.
Neonates are typically infected transplacentally or by birth through an infected birth canal.
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.7 In 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).
DIAGNOSIS AND TREATMENT
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 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
The drug of choice for the treatment of listeriosis is ampicillin in combination with gentamicin. For patients allergic to penicillin or aminoglycosides, trimethoprim-sulfamethoxazole is the alternative of choice. Cephalosporins have poor activity against Listeria. The recommended treatment duration is 10 to 14 days for nonmeningitic invasive infection and 14 to 21 days for L monocytogenes meningitis.1Treatment with 14 days of ampicillin during pregnancy may prevent fetal or perinatal infection and its sequelae.1
Prevention relies on decreasing the risk of exposure. Public health measures to control and monitor contamination of ready-to-eat foods has resulted in a significant decrease in invasive listeriosis since 1996, including a 37% reduction in pregnancy-associated disease.22 The consumer should thoroughly cook raw food from animal sources, wash raw vegetables, avoid unpasteurized dairy products, avoid contamination of cooking utensils with uncooked foods, use careful handwashing after contact with uncooked food, and disinfect the interior of refrigerators. High-risk persons should also avoid consumption of soft cheeses, reheating leftover food or ready-to-eat food, and consumption of cold cuts if unable to reheat them thoroughly.12