Listeriosis reservoir

Clinical Manifestations

The incubation period for invasive listeriosis [time from ingestion of contaminated food to illness] averages about 11 days; 90% is within 28 days.10 Invasive listeriosis in an immunocompromised adult is most often manifested as bacteremia without an obvious focus. In such cases, patients have nonspecific complaints, such as fever, malaise, myalgia, and back pain. Bacteremia is the form of invasive listeriosis that complicates pregnancy; CNS infection in pregnancy is extremely rare in the absence of other risk factors. Listeriosis during pregnancy may lead to spontaneous abortion or neonatal sepsis, but early antimicrobial therapy may result in the birth of a healthy child. Endocarditis withL. monocytogenes can occur on both native and prosthetic valves and carries a high rate of septic complications.11 Endocarditis, but not bacteremia per se, may be a clue to underlying colon cancer; colonoscopy should be considered in all cases of listerial endocarditis.

Persons in whomL. monocytogenes bacteremia develops may progress to CNS infection [neurolisteriosis], most commonly manifested as meningitis.Listeria has a predilection for infecting brain tissue as well as the meninges, and unlike other common bacterial causes of meningitis, it not infrequently causes encephalitis or brain abscess. Brain abscess as a result of infection byL. monocytogenes exhibits unusual features compared with other bacteria: listerial brain abscess coexists with bacteremia in nearly all cases and with meningitis in one fourth; in addition, abscesses are often subcortical.12

L. monocytogenes is the most common cause of bacterial meningitis in patients with lymphomas, organ transplant recipients, and patients treated with corticosteroids for any reason. Affected persons usually have the classic acute symptoms of meningitis, but the presentation is subacute [>24 hours] in 60% of cases. Nuchal rigidity is absent in 20%. Focal neurologic findings, including ataxia, tremors, myoclonus, and seizures, may be seen, consistent with the tropism ofListeria for brain parenchyma. Gram stain of cerebrospinal fluid [CSF] reveals small gram-positive rods in only about one third of cases. The glucose content in CSF is normal in more than 60% of cases; mononuclear cells predominate in 30%.

Listerial rhombencephalitis is an unusual form of listerial encephalitis that involves the brain stem and, unlike other listerial CNS infections, usually occurs in healthy adults. The typical clinical picture is one of a biphasic illness with a prodrome of fever, headache, nausea, and vomiting lasting about 4 days, followed by the abrupt onset of asymmetrical cranial nerve deficits, cerebellar signs, and hemiparesis or hemisensory deficits or both. Respiratory failure develops in about 40% of patients. Nuchal rigidity is present in about half, and CSF findings are only mildly abnormal, with a positive CSF culture in about 40%. Almost two thirds of patients are bacteremic. Magnetic resonance imaging is superior to computed tomography for demonstrating rhombencephalitis. Mortality is high, and serious sequelae are common in survivors.

Listeriosis

Listeriosis is caused byListeria monocytogenes, a non-spore-forming, short, Gram-positive bacillus. It is an intracellular pathogen that is able to survive and multiply within host phagocytic cells. Listeriosis primarily affects older adults, pregnant women, neonates, and immunocompromised hosts. Listeria is found in soil and decaying vegetable matter. It is also found in the intestinal tracts of several mammals, birds, fish, and crustaceans. In adults, most infections are thought to arise from oral ingestion of contaminated material, leading to intestinal mucosal penetration and systemic infection. Impaired cell-mediated immunity and macrophage function are associated with increased susceptibility to infection with Listeria.107 In pregnant women, the bacterium is able to cross the placenta during maternal bacteremia and infect the fetus. Infection in pregnant women can lead to spontanous abortion, stillbirth, preterm labor, or neonatal infection.

In a systematic review of peer-reviewed literature, the WHO estimated that listeriosis resulted in 23,150 illnesses worldwide in 2010 leading to 5463 deaths. In this review of listeriosis cases, 20.7% were perinatal infections with septicemia occurring in 30.7% of infected neonates.24 Most cases of listeriosis occur as sporadic illnesses, likely after ingestion of contaminated food. Several foodborne outbreaks have also been reported and are associated with a variety of foods. The most common foods implicated in infections are delicatessen meats, hot dogs, soft cheeses, smoked seafood, and pâtés.

Among all organisms causing neonatal sepsis,L. monocytogenes is a relatively uncommon cause. Listeria infection in neonates is classified as early onset or late onset. The signs and symptoms of listeriosis in neonates are indistinguishable from the signs and symptoms of other postnatal bacterial infections. Early-onset disease is most often acquired by transplacental transmission, and affected infants are symptomatic soon after birth. Meconium passage is often associated with intrauterine Listeria infection. Common manifestations of early-onset infection include neonatal sepsis and pneumonia. Late-onset infection may be acquired by vertical transmission from a colonized mother during passage through the birth canal or by transmission from other colonized or infected caregivers. Symptoms usually arise after the first week or two of life. The most common manifestation of late-onset listeriosis is meningitis, often with insidious onset.

As for any neonate with suspected sepsis, blood and CSF cultures should be obtained. In addition, isolation ofL. monocytogenes from cultures of amniotic fluid or placental tissue may support the diagnosis of early-onset disease. Recommended empiric antibiotic treatment for neonatal sepsis includes ampicillin and an aminoglycoside. This regimen provides important coverage for listeriosis, as cephalosporins have no activity againstL. monocytogenes. When infection with Listeria has been confirmed, the antibiotic of choice is ampicillin. The addition of gentamicin is recommended to provide synergy. After the patient demonstrates clinical improvement, gentamicin can be discontinued and ampicillin given alone to complete the remainder of treatment. For all cases of Listeria meningitis, a repeat lumbar puncture should be performed 1-2 days after the start of treatment to confirm sterilization of the CSF. Treatment duration of 10-14 days is recommended for uncomplicated bacteremia. For meningitis, treatment should be continued for 14-21 days. All patients with Listeria meningitis should have neuroimaging obtained near the anticipated end of treatment to determine whether there is parenchymal involvement and whether the patient may require a more prolonged course of treatment.

Prognosis

Neonatal listeriosis accounts for the largest recognizable group of infections caused by L. monocytogenes. Fetal loss with early gestational infection is a recognized complication of maternal infection. In late gestational maternal infection, sparing of the fetus has been reported [266], but it is likely uncommon unless antepartum antibiotic treatment has been given to the mother [267,268].

Although fetal or neonatal infection with L. monocytogenes is known to have a high fatality rate, the long-term morbidity is unclear. Rotheberg and associates [269] found an increased incidence of developmental delay assessed at a mean age of 29.5 months among small [