AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Listeria monocytogenes, although an uncommon cause of illness in the general population, is an important pathogen in pregnant patients, neonates, elderly individuals, and immunocompromised individuals. It is typically a food-borne organism. Listeria is also a common veterinary pathogen, being associated with abortion and encephalitis in sheep and cattle. It can be isolated from soil, water, and decaying vegetation.

The most common clinical manifestation is diarrhea. A mild presentation of fever, nausea, vomiting, and diarrhea may resemble a gastrointestinal illness.¹ The microorganism has gained recognition because of its association with epidemic gastroenteritis. In 1997, an outbreak of noninvasive gastroenteritis occurred in 2 schools in northern Italy, involving more than 1500 children and adults.²

Bacteremia and meningitis are more serious manifestations of disease that can affect individuals at high risk. Unless recognized and treated, Listeria infections can result in significant morbidity and mortality.

Pathophysiology

L monocytogenes is a motile, non–spore-forming, gram-positive bacillus that has aerobic and facultatively anaerobic characteristics. It grows best at neutral to slightly alkaline pH and is capable of growth at a wide range of temperatures, from 1-45°C. It is beta-hemolytic and has a blue-green sheen on blood-free agar. It exhibits characteristic tumbling motility when viewed with light microscopy and is difficult to isolate in mixed cultures. It may be mistaken for streptococci or contaminants such as corynebacteria.

Most infections occur after oral ingestion, with access to the systemic circulation after intestinal penetration. Protection against Listeria is mediated via lymphokine activation of T cells on macrophages and by interleukin-18.

CNS infection may manifest as meningitis, meningoencephalitis, or abscess. Endocarditis is another possible presentation. Localized infection may manifest as septic arthritis, osteomyelitis, and, rarely, pneumonia.

Frequency

United States

The frequency of L monocytogenes infection is 9.7 cases per million population. Annually, 2500 cases are reported, with higher incidence rates during the summer months.³ Pregnant women account for 27% of all cases, and most occur during the third trimester. Seventy percent of all nonperinatal infections occur in immunocompromised patients. Corticosteroid therapy is the most important predisposing association in patients who are not pregnant.

Mortality/Morbidity

• The overall mortality rate of L monocytogenes infection is 20-30%.
• Of all pregnancy-related cases, 22% resulted in fetal loss or neonatal death, but mothers usually survive.

Sex

• With the exception of pregnant women, no sex predilection is recognized.

Age

• Women of childbearing age are commonly affected.
• Neonates and elderly individuals are at risk.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

Disease may be a self-limited gastrointestinal tract illness or a more severe CNS infection or bacteremia.

Physical

Examination depends on the organ system involved.

• Infection in pregnancy^{4, 5}
• • Listeria may proliferate in the placenta and cause infection due to impaired cell-mediated immunity during pregnancy.
  • CNS infection is very rare during pregnancy, although it is observed frequently in other compromised hosts.
  • Fever, myalgias, arthralgias, back pain, and headache are classic symptoms of bacteremia. Symptoms may mimic those of a flulike illness. The infection may be mild and self-limited.
  • Listeriosis during pregnancy usually occurs during the third trimester, when cell-mediated immunity is at its lowest.
  • Preterm labor and/or delivery is common. Abortion, stillbirth, and intrauterine infection are possible.
• Neonatal infection (granulomatosis infantisepticum): Two forms are described.⁴
• • Early-onset sepsis, with Listeria acquired in utero via transplacental transmission, results in premature birth. Listeria can be isolated in the placenta, blood, meconium, nose, ears, and throat, among other sites, and manifests as abscesses and/or granulomas.
  • Late-onset meningitis is acquired through vaginal transmission, although it also has been reported with cesarean deliveries.
• CNS infection⁶
• • Listeria has a predilection for the brain parenchyma, especially the brain stem, and the meninges.
  • Mental status changes are common.
  • Seizures, both focal and generalized, occur in at least 25% of patients.
  • Cranial nerve deficits may be present.
  • Strokelike syndromes with hemiplegia may occur.
  • Nuchal rigidity is less common.
  • Movement disorders may include tremor, myoclonus, and ataxia.
  • Patients may present with encephalitis, especially of the brainstem.⁷
  • Meningitis is possible.
  • Ventriculitis, particularly of the fourth ventricle, may develop.
  • Cervical myelitis has been reported.⁸
  • Brain abscess occurs in 10% of CNS infections, often located in the thalamus, pons, and medulla. This uncommon complication is associated with high mortality.⁹
• Febrile gastroenteritis¹
• • L monocytogenes can produce food-borne diarrheal disease, which is typically noninvasive.
  • The median incubation period is 1-2 days, with diarrhea lasting anywhere from 1-3 days.
  • The prevalence of diarrheal illness is high in individuals exposed to inocula of Listeria.
  • Patients present with fever, myalgias, and diarrhea and recover with supportive care.

Causes

• Most infections are due to food-borne transmission.
• A substantial minority of infections are transmitted by other modes.
• • Transmission can occur transplacentally or via an infected birth canal.
  • Isolated incidences of cross-infection in neonatal nurseries have been reported.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Meningeal carcinomatosis
Lymphomatous meningitis
Multiple sclerosis
Vasculitis
Viral encephalitis or meningitis
Fungal meningitis
Brain abscess
Bacterial meningitis
Septic abortion
Pyelonephritis in pregnancy

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Blood cultures should be performed. Blood culture results are positive in 60-75% of patients with CNS infections.
• Listeria demonstrates "tumbling motility" in wet mounts of cerebrospinal fluid (CSF). Listeria organisms are motile in wet mounts of CSF.
• CSF Gram stain results are positive in less than 50% of patients. CSF analysis reveals pleocytosis, and CSF protein levels are moderately elevated. CSF glucose levels may be low, and if so, are associated with a poor prognosis.
• Laboratory results that show diphtheroids should prompt heightened awareness for the possibility of Listeria infection, particularly in immunocompromised patients.
• CSF culture findings are positive in nearly 100% of patients.
• Serologic testing is not reliable.
• Stool cultures are neither sensitive nor specific.

Imaging Studies

• MRI is superior to CT scan for demonstrating CNS disease, especially in the brainstem.¹⁰
• Transesophageal echocardiography should be performed if endocarditis is suspected.

Procedures

• Lumbar puncture should be performed if CSF infection is suspected.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• Intravenous antibiotics must be started immediately when the diagnosis is suspected or confirmed.
• Diagnosis is established by culture of the organism from blood, CSF, or other sterile body fluid.
• Person-to-person transmission does not occur; therefore, isolation precautions are not necessary.

Consultations

Listeriosis may be sporadic or may be part of a larger epidemic. The table below lists some of the most recent epidemics. Consultation with an infectious disease specialist or an epidemiologist is important when epidemic listeriosis is suspected.

Epidemic Listeriosis

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Antibiotic therapy is the treatment of choice. Bacteremia should be treated for 2 weeks if the patient is immunocompetent. Longer courses may be required in the immunocompromised patient. Meningitis should be treated for 3 weeks; endocarditis, for 4-6 weeks; and brain abscess, for at least 6 weeks. Ampicillin is generally considered the preferred agent, but other agents may be acceptable. Gentamicin is added frequently for synergy, but it may be discontinued after 1 week of clinical improvement in order to decrease the chance of renal toxicity or ototoxicity.¹⁹

Drug Category: Antibiotics

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Deterrence/Prevention

• Cook all raw food thoroughly.
• Wash raw vegetables.
• Avoid consumption of raw (unpasteurized) milk or milk products.
• Wash hands, knives, and cutting boards after handling uncooked foods.
• Pregnant or immunocompromised patients should avoid soft cheeses (eg, feta, Brie, Camembert, bleu). Cream cheese, yogurt, and cottage cheese are allowed.
• Reheat leftover or ready-to-eat foods (eg, hot dogs) until steaming hot.
• Avoid delicatessen foods unless they are thoroughly reheated.
• Cook food to a safe internal temperature.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• US regulatory agencies recommend a recall when L monocytogenes is detected in processed foods that are eaten without cooking.
• • The United States Department of Agriculture's Food Safety and Inspection Service has issued new regulations for ready-to-eat meat and poultry processing plants by outlining a program to control and test for L monocytogenes.¹¹
  • Systems have not been perfected; therefore, patient education is most effective in prevention.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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Article Last Updated: Jun 23, 2008