Description

• An infection caused by the ubiquitous, weakly hemolytic, gram-positive bacillus Listeria monocytogenes; pathogenic to many species
• Occurs most often in fetuses (disseminated infantile listeriosis), neonates, and immunosuppressed patients
• Most affected adults have preexisting disease (e.g., cirrhosis, lymphomas, solid tumors, AIDS, cancer therapy, organ transplant recipients) or are on corticosteroid therapy.
• Usual course: acute

Pediatric Considerations

• Infected fetuses are often stillborn or premature.
• Up to 50% mortality in treated neonates

Epidemiology

Incidence

• U.S. foodborne listeriosis: 0.3/100,000 people
• 2011: A 28-state outbreak from contaminated cantaloupes infected 146 people, with 30 deaths.
• Particularly affects neonates (<1 month) and elderly (>60 years)
  • Predominant sex: male > female
  • 500 annual deaths from listeriosis in the United States
  • 20–65% of all foodborne infection–related deaths in the United States are due to listeriosis.
  • Pregnant women account for 27% of all Listeria cases and ~60% of cases from ages 10 to 40 years.
  • ~70% of nonperinatal infections occur in immunocompromised patients.
  • Neonates can have early (<7 days) or late-onset (>7 days) infection.
  • Most cases of listeriosis are sporadic (not associated with an outbreak).
  • Listerial meningitis has a mortality rate of 20%.

Prevalence

• Symptoms ~20 times more likely to manifest in pregnancy
• Listeriosis is ~300 times more likely in HIV/AIDS patients than in age-matched population.

Etiology and Pathophysiology

• L. monocytogenes, a small gram-positive bacillus is the primary pathogen; infection with other Listeria species is rare.
• There are at least 13 serotypes of L. monocytogenes, but most disease is due to types 4b, 1/2 a, and 1/2 b.
• Incubation period for invasive illness is not well-established and is highly variable because it depends on bacterial load and host immunity.
• Listeria replicates best at room temperature but can grow at refrigerator temperatures.
• Listeria has a unique intracellular life cycle.
• After entering GI tract, Listeria is phagocytosed by active endocytosis and enters host without disturbing the normal GI mucosal structure.
• Hematogenous dissemination occurs through the bloodstream; crosses placental and blood–brain barriers
• Illness begins 2 to 70 days after contaminated food consumption.
• Extremely common in food supply: Listeria recovered from 15–70% of raw vegetables, fish, meat, ice cream, and unpasteurized milk
  • Deli meat is the highest risk ready-to-eat food source for L. monocytogenes; retail-sliced deli meats have higher rates than prepackaged.
• Isolated in stool of 5% of asymptomatic adults
• Resistance to Listeria infection is cell-mediated.

Risk Factors

• Age: fetus, neonate, elderly
• Metastatic malignant disease
• HIV infection; alcoholism
• Renal hemodialysis
• Immunosuppression (including corticosteroid therapy)
• Exposure to infected animals (veterinarians, butchers); animal-to-human transmission is rare.
• Ingesting contaminated food or drink (soft cheeses, milk, butter, pate, cold-smoked trout, hot dogs, ready-to-eat pork, and deli meats)
• Pregnancy; fetal and neonatal disease have high mortality; difficult to diagnose in pregnancy because patients are often asymptomatic or present with a flulike illness; requires prompt treatment to prevent fetal transfer
• Use of proton pump inhibitors
• Prior to hospitalization; 40% of cases exposed to high-risk foods during hospitalization (1)[C]
• Colonoscopy

General Prevention

• Counseling of pregnant women regarding the increased risk of listeriosis during pregnancy
• http://www.usda.gov/wps/portal/usda/usdahome for updates on recalled foods
• Avoid handling livestock.
• Avoid contaminated silage and sewage.
• Avoid raw/unpasteurized dairy products.
• Avoid soft cheeses (Mexican and feta).
• Wash all raw vegetables carefully.
• Wash hands after handling uncooked foods.
• Cook leftovers, hot dogs, cold cuts, and deli meats adequately before eating.
• Listeriosis can be effectively prevented with trimethoprim-sulfamethoxazole in organ transplant and AIDS patients (2)[B].

Commonly Associated Conditions

• Pregnancy
• Immunodeficiency; diabetes
• Cirrhosis; hemochromatosis and iron overload (Iron is a virulence factor for Listeria.)
• Lymphoma; leukemia
• Solid tumors; organ transplant recipients
• Chronic renal disease
• Alcoholism
• Age >60 years