- 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
- Infected fetuses are often stillborn or premature.
- Up to 50% mortality in treated neonates
- 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%.
- 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.
- 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]
- 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.
Commonly Associated Conditions
- Immunodeficiency; diabetes
- Cirrhosis; hemochromatosis and iron overload (Iron is a virulence factor for Listeria.)
- Lymphoma; leukemia
- Solid tumors; organ transplant recipients
- Chronic renal disease
- Age >60 years
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