(See Neonatal Listeriosis Neonatal Listeriosis Neonatal listeriosis is acquired transplacentally or during or after delivery. Symptoms are those of sepsis. Diagnosis is by culture or polymerase chain reaction testing of mother and infant... read more .)
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, 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 and is 18 times more frequent in pregnant women.
Transmission
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.
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
Older people
Pregnant women are also at increased risk of developing listerial infection, which is usually mild. However, the infection can spread antepartum and intrapartum from mother to child and can cause abortion, stillbirth, premature birth, or early infant death.
Listeria can cause life-threatening infection in the neonate, including bacteremia Neonatal Listeriosis Neonatal listeriosis is acquired transplacentally or during or after delivery. Symptoms are those of sepsis. Diagnosis is by culture or polymerase chain reaction testing of mother and infant... read more and pneumonia Neonatal Pneumonia Neonatal pneumonia is lung infection in a neonate. Onset may be within hours of birth and part of a generalized sepsis syndrome or after 7 days and confined to the lungs. Signs may be limited... read more , and are a common cause of neonatal bacterial meningitis Neonatal Bacterial Meningitis Neonatal bacterial meningitis is inflammation of the meninges due to bacterial invasion. Signs are those of sepsis, central nervous system irritation (eg, lethargy, seizures, vomiting, irritability... read more .
Symptoms and Signs of Listeriosis
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.
Diagnosis of Listeriosis
Culture
Listerial infections are diagnosed by culture of blood or cerebrospinal fluid. 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 weeks after onset.
Treatment of Listeriosis
Ampicillin or penicillin G, usually with an aminoglycoside
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 Organism-specific antibiotic therapy Organism-specific antibiotic therapy Neonatal bacterial meningitis is inflammation of the meninges due to bacterial invasion. Signs are those of sepsis, central nervous system irritation (eg, lethargy, seizures, vomiting, irritability... read more .
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.
Prevention of Listeriosis
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, older people). 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 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.
