Not Found

Find information on medical topics, symptoms, drugs, procedures, news and more, written for the health care professional.


By Larry M. Bush, MD, Affiliate Professor of Clinical Biomedical Sciences; Affiliate Associate Professor of Medicine, Charles E. Schmidt College of Medicine, Florida Atlantic University; University of Miami-Miller School of Medicine
Maria T. Perez, MD, Associate Pathologist, Department of Pathology and Laboratory Medicine, Wellington Regional Medical Center, West Palm Beach

Click here for
Patient Education

Listeriosis is bacteremia, meningitis, cerebritis, dermatitis, an oculoglandular syndrome, intrauterine and neonatal infections, or rarely endocarditis caused by Listeria sp. Symptoms vary with the organ system affected. Intrauterine infection may cause fetal death. Diagnosis is by laboratory isolation. Treatment includes penicillin, ampicillin (often with aminoglycosides), and trimethoprim/sulfamethoxazole.

Listeria are small, non–acid-fast, noncapsulated, nonsporulating, beta-hemolytic, aerobic, and facultative anaerobic gram-positive bacilli that have characteristic tumbling motility. They are present worldwide in the environment and in the gut of humans, nonhuman mammals, birds, arachnids, and crustaceans. There are several species of Listeria, but L. monocytogenes is the primary pathogen in humans.

In the US, the average annual incidence of laboratory-confirmed listeriosis is about 2.6/million, peaking in the summer. Attack rates are highest in neonates, in adults ≥ 60 yr, and in immunocompromised patients, including patients with HIV/AIDS. Listeriosis is 300 times more common among patients with HIV/AIDS than among the general population.


Because L. monocytogenes is ubiquitous in the environment, opportunities for contamination are numerous during the food production process. Nearly all types of food can harbor and transmit L. monocytogenes, but infection usually occurs via ingestion of contaminated dairy products, raw vegetables, meats, or, particularly, refrigerated foods that require no cooking before they are eaten. Contamination is favored by the ability of L. monocytogenes to survive and grow at refrigerator temperatures.

Infection may also occur by direct contact and during slaughter of infected animals.

Pearls & Pitfalls

  • Listeria monocytogenes can reproduce at refrigerator temperatures, so lightly contaminated refrigerated food can become heavily contaminated.

Risk factors

Because L. monocytogenes multiplies intracellularly, control of listeriosis requires cell-mediated immunity; thus, the following people are at high risk:

  • Immunocompromised patients

  • Neonates

  • Elderly

Pregnant women are also at increased risk of developing listerial infection, which can spread antepartum and intrapartum from mother to child and can cause abortion or early infant death.

Listeria are a common cause of neonatal bacterial meningitis.

Symptoms and Signs

Primary listerial bacteremia is rare and causes high fever without localizing symptoms and signs. Endocarditis, peritonitis, osteomyelitis, septic arthritis, cholecystitis, and pleuropneumonia may occur. Febrile gastroenteritis may occur after ingestion of contaminated food. Listerial bacteremia during pregnancy can cause intrauterine infection, chorioamnionitis, premature labor, fetal death, or neonatal infections.

Meningitis is due to Listeria in about 20% of cases in neonates and in patients > 60 yr. Twenty percent of cases progress to cerebritis, either diffuse encephalitis or, rarely, rhombencephalitis and abscesses; rhombencephalitis manifests as altered consciousness, cranial nerve palsies, cerebellar signs, and motor or sensory loss.

Oculoglandular listeriosis can cause ophthalmitis and regional lymph node enlargement (Parinaud syndrome). It may follow conjunctival inoculation and, if untreated, may progress to bacteremia and meningitis.


  • Culture

Listerial infections are diagnosed by culture of blood or CSF. The laboratory must be informed when L. monocytogenes is suspected because the organism is easily confused with diphtheroids.

In all listerial infections, IgG agglutinin titers peak 2 to 4 wk after onset.


  • Ampicillin or penicillin G, usually with an aminoglycoside

Listerial meningitis is best treated with ampicillin 2 g IV q 4 h. Most authorities recommend adding gentamicin (1 mg/kg IV q 8 h) based on synergy in vitro. Cephalosporins are not effective. For treatment of neonatal meningitis, see Neonatal Bacterial Meningitis : Organism-specific antibiotic therapy.

Endocarditis and primary listerial bacteremia are treated with ampicillin 2 g IV q 4 h plus gentamicin (for synergy) given for 6 wk (for endocarditis) or 2 wk (for bacteremia) beyond defervescence. Oculoglandular listeriosis and listerial dermatitis should respond to erythromycin 10 mg/kg po q 6 h, continued until 1 wk after defervescence. Cephalosporins have no in vitro activity and should not be used; failures with vancomycin have been reported. Trimethoprim/sulfamethoxazole 5/25 mg/kg IV q 8 h is an alternative. Linezolid is active in vitro, but clinical experience is lacking.


Because food contamination is common and because L. monocytogenes can reproduce at refrigerator temperatures, lightly contaminated food can become heavily contaminated during refrigeration. This problem is of particular concern when foods (eg, refrigerated ready-to-eat foods) are eaten without further cooking. Thus, appropriate food hygiene is important, particularly for at-risk people (eg, immunocompromised patients, pregnant women, the elderly). Those at risk should avoid eating the following:

  • Soft cheeses (eg, feta, Brie, Camembert)

  • Refrigerated ready-to-eat foods (eg, hot dogs, deli meats, pȃtés, meat spreads), unless they are heated to an internal temperature of 73.9° C (165° F) or until steaming hot just before serving

  • Refrigerated smoked seafood (eg, nova-style, lox, kippered, smoked, jerky), unless it has been cooked

  • Raw (unpasteurized) milk

Key Points

  • L. monocytogenes is very common in the environment but causes infection in only about 2.6 people/million annually in the US, typically via contaminated food products.

  • Attack rates are highest in neonates, adults 60 yr, and immunocompromised patients.

  • Various organ systems can be affected; maternal infection during pregnancy may cause fetal death.

  • Give ampicillin, usually plus gentamicin.

  • Advise high-risk patients to prevent disease by not eating foods most likely to be contaminated.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • No US brand name