(See Neonatal Listeriosis.)
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, there are about 1800 cases of listeriosis annually, peaking in the summer. Attack rates are highest in neonates, in adults ≥ age 60, 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.
Because L. monocytogenes multiplies intracellularly, control of listeriosis requires cell-mediated immunity; thus, the following people are at high risk:
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.
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 up to 20% of cases in neonates and in patients > age 60. 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.
Listerial meningitis is best treated with ampicillin 2 g IV every 4 hours. Most authorities recommend adding gentamicin (1 mg/kg IV every 8 hours) 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 every 4 hours plus gentamicin (for synergy) given for 6 weeks (for endocarditis) or 2 weeks (for bacteremia) beyond defervescence. Oculoglandular listeriosis and listerial dermatitis should respond to erythromycin 10 mg/kg orally every 6 hours, continued until 1 week 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 every 8 hours 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
L. monocytogenes is very common in the environment but causes infection in only about 1800 people annually in the US, typically via contaminated food products.
Attack rates are highest in neonates, adults ≥ age 60, 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.