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Listeria monocytogenes infections in neonates
Listeria monocytogenes Infections in Neonates Robert Bortolussi, MD, FR CPC Listeria monocytogenes continues to be a major bacterial pathogen for newborn infants in North America. Neonatal listeriosis accounts for approximately 30 percent of the total listeriosis cases reported in the United States. Foodborne outbreaks of listeriosis have been attributed to dairy products and ready-to-eat prepared foods. During outbreaks, a disproportionately high number of cases occur as perinatal infection. In newborns, the high susceptibility to Listeria probably is attributable to delayed activation of macrophages. Production of tumor necrosis factor-~ (TNF-~) and interleukin-12 (IL-12), which are essential mediators of host defense against Listeria, are produced in lower concentrations by infected newborn mononuclear cells. The clinical manifestations of listeriosis are well known. Perinatal infection often is associated with a preceding flulike disease in the pregnant woman. Maternal bacteremia may be present at this stage. Premature labor is common; approximately 70 percent of infected mothers deliver before 35 weeks' gestation. Among infants, two clinical syndromes are identified, early-onset and late-onset listeriosis. Early-onset infection is associated with overwhelming sepsis and a high mortality rate. Late-onset infection, occurring between 7 and 90 days of life, is less severe; however, a high proportion of cases have meningitis. Ampicillin in combination with an aminoglycoside is the preferred treatment for neonatal listeriosis. Removal of Listeria-contaminated food through strict adherence to regulatory standards has led to a decreased incidence of listeriosis in the United States since the early 1990s. Although the incidence of epidemic disease is decreasing in the United States, sporadic cases still do occur. All cases must be identified and treated early to achieve optimal outcome. A high index of suspicion and early intervention are essential. Copyright 9 1999 by W.B. Saunders Company
L
isteria monocytogenes is a short, motile, gram-positive, non-
spore-forming bacillus that has been isolated from a variety of animal species in association with disease, l The history of the organism was summarized by McLauchlin 1 in 1987. Listeria was first described in 1926 by Murray, Webb, and Swann, who discovered it while investigating an epidemic of infection among laboratory rabbits and guinea pigs. At that time, it was given the name Bacterium monocytogenes because infection in the animals was characterized by monocytosis. Three years later, Nyfeldt isolated B monocytogcnesfrom the blood of a patient with an infectious mononucleosis-like disease. It was not until 1936 that the first human perinatal infection was documented. The name of the organism was changed to Listeria monocytogenes in 1940. 2 Six serovars o f L monocytogenes have been described and are distinguished on the basis of somatic O and flagellar H anti-
From the Departments of _Pediatrics and Microbiology and Immunology, Dalhousie University,Halifax, Nova Scotia, Canada. Address correspondenceto RobertBortolussi,M_D,FRCPC, 1WK GraceHealth Centre,5850 UniversityAve, Halifax, NS, CanadaB3J 3G9. Copy@t 9 1999 by W.B. Saunders Company 1045-1870/99/1002-0007510.00/0
gens. 3 Serovars 1/2a, 4a, and 4b are the most common isolates from animals and humans with clinical disease. In the United States, serovars 4b and 1/2a account for 95 percent of strains, with serotype 4b being the most common overall. Other serovars originate from soil or other environmental sources but rarely are seen as clinical pathogens.
Epidemiology Recent evidence suggests that most, if not all, human cases of L
monoqytogenes are acquired through ingestion of contaminated food.4,5 The first outbreak that convincingly showed transmission via a foodborne source was reported from the Atlantic Maritime provinces of Canada. 6 Several outbreaks have been attributed to consumption of inadequately pasteurized dairy products. 7,s However, when properly conducted, pasteurization should eliminate Listeria. The improved ability to culture L monocytogeneswith selective media has provided an opportunity to examine specific foods in nonepidemic cases of listeriosis. Epidemiological and microbiological investigations of patients and foods present in the homes of these patients have produced increasing evidence pointing to the important role of food in transmission of these sporadic
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cases of listeriosis.5'9'm Although L monog;togenes is isolated frequently from foods, contaminated foods likely to cause listeriosis are characterized as ready-to-eat foods, foods containing higher concentrations ofL monocytogenes, and foods containing serotype 4b. These studies implicated undercooked chicken and soft cheeses as significant sources of disease and are supported by sampling surveys conducted by regulatory agencies. Active surveillance in the United States suggests an annual incidence of 0.7 cases per 100,000 population.8 Approximately 1,700 cases of listeriosis occur annually in the United States, with a mortality rate of 40 percent. Slightly lower figures have been reported recently from Europe. For neonatal llsteriosis, the incidence in the United States is approximately 13 cases per 100,000 live births, 30 percent of the total number of cases of reported listeriosis. Similar incidence rates have been reported in studies from Europe. Of interest, epidemics of foodborne listeriosis have disproportionately involved perinatal cases.8,H No differences in carriage rates between pregnant women and nonpregnant individuals have been found in fecal and vaginal specimens. The possibilitythat a lower infective dose is needed to cause disease in pregnant women and immunocompromised patients has been proposed but not confirmed. The risk of listeriosis varies among segments of the population. Two thirds of cases of llsteriosis in adults occur in immunocompromised patients. Renal transplantation appears to be a particularly- significant risk factor. Listeriosis also is reported in patients with AIDS, who have a 1,000-fold risk of acquiring invasive Iisteriosis. Although most large outbreaks ofllsteriosis have occurred in the community, case clusters of nosocomial listeriosis in both newborn infants and adults have been described. The index case in one nosocomial outbreak was diagnosed as "early-onset" newborn infection (within 1 week of birth). 12 In this outbreak, the index case was not symptomatic at birth and was bathed with mineral oil that then became contaminated with the epidemic isolate. Subsequent bathing of other infants with the same oil led to "late-onset" disease in other infants.
Pathogenicity Because L monocytogenes is a low-grade intracellular pathogen, it has been used extensively in animal models to gain an understanding of the cell-mediated immune syst)m. Microbial attachment to host cells is the initial step in cell invasion. Recent work has shown that interaction with a heparan sulfate peptidoglycan receptor on the surface of cells is involved in L mono~ytogenes adhesion.IS A family of surface proteins known as internalins are secreted in large amounts by all strains of Listeria capable of invading host cells. Although these proteins may identify an important factor associated with entrance into epithelial cells and hepatocytes, they do not explain intracellular spread and multiplication. The intracellular survival of Listeria also requires synthesis of a specific hemolysin, termed llsteriolysin O, which lyses the phagosomal membrane. Release ofL monocytogenesfrom intracellular vacuoles precipitates both intracellular growth and polymerization of actin of the host cell around Listeria. Actin
polymerization is important in the cell-to-cell transfer of L mono~togenes and is encoded by the ActA gene. 14 The liberated organism thrives in the cytoplasm, which provides better growth conditions. Through these mechanisms, Listeria can enter, grow, and spread inside a wide variety of cells, including renal epithelial cells, fibroblasts, vascular endothelium, hepatocftes, and enterocytes. By producing ActA, Listeria causes host-cell actin to assemble into filaments at one end of the bacterium. This "rocket tail" provides the propulsive force for the organism to move through the cytoplasm (Fig 1). When the bacteria reachthe cell membrane, they form filipods that enter adjacent cells. The process leading to acquired immunity to Listeria is now clearer. In immunocompetent adults, Listena is phagocytosed by both "professional" phagocytes (macrophages, monocytes) and "nonprofessional" phagocytic cells (fibroblasts, hepatocytes). Macrophages take up and process llsterial proteins and produce interleukin (IL)- 12 and IL- 1.15Peptides resulting from digestion of Listeria are actively processed by the macrophage in the endoplasmic reticulum, where the peptides bind to major histocompatibility complex (MI-IC) class I moleculesJ 6 The Listeria-peptide-MHC complex is transported to the cell surface, where it is recognized by cytotoxic T cells (CD8 phenotype) and helper T ceils (T~). In the presence of IG12, naive TH cells, differentiate into TH-1 cells, which proliferate and produce IL-2, 9 15Interleukin-12 also stimuinterferon (IFN)-',/, and lymph otoxm. lates activation and proliferation of natural killer (NK) cells. Both cell clones produce IFN-% Cytotoxic T cells interact with cells bearing L mono~togenes antigens, causing them to lyse. Natural killer cells are further stimulated by WN-',/, inducing an enhanced ability of these cells to lyse infected fibroblasts and hepatocytes. Peak immunity to Listeria is expressed about the sixth day of infection, which coincides with maximal T-cell synthesis of IFN-% 17,m Macrophage colony-stimulating factor (M-CSF) and tumor necrosis factor (TNF)-ot also appear during the first 5 days and have been implicated as mediators oflisterial clearance. TNF-ct enhances a variety of antibacterial or antiparasitic resistance mechanisms. Monocytes and macrophages probably are the most abundant source of TNF-a. Endotoxin (LPS) and other agents, including mitogens, viruses, and cytokines such as M-CSF, K-l, IL-2, and IFN-% have been identified as inducers of TNF-ot. When administered before infection, TNF-et inducers enhance resistance of the host to bacterial infection. TNF-ot produced endogenously during sublethal Listeria infection in adult animals appears to function as an inducer of resistanc@ 9 suggesting that TNF-et-dependent mechanisms limit intracellular infection early in the course. The pathogenesis of fetal listeriosis is not understood as clearly. Because the heaviest loci for neonatal infection are the lungs and gut, probably the fetus is infected by swallowing contaminated liquor, as well as through the transplacental hematogenous route. 2~ An ascending pathway from the lower genital tract may occur, but infection via the transplacental route is favored by most experts. L mono~togenes chorioamnionitis diagnosed by transabdorninal amniocentesis (free from vaginal bacterial contamination) has been reported and, thus, indicates a maternal-to-newborn blood-borne route of infection. In newborn animals, susceptibilityto Listeria is increased and is associated with delayed activation of macrophages. Studies on the afferent and efferent arms of the immune system in
NeonatalListeriosis
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II
Figure
1. Electron micrograph of a cell containing several ingested organisms. In several (arrows), the organism appears to have escaped into the cytosome of the cell with formation of a "rocket tail" of the organism. The solid bar represents approximately
1/xm. newborn mice have shown that macrophage-T-lymphocyte interaction is impaired, a n d macrophage activation does not occur.22 TNF-e~ is decreased among newborn rats challenged with L monocytogenes, in which TNF-e~ was detected only among animals older than 8 days. 23 The age at which TNF-e~ becomes measurable corresponds to the approximate age at which increased resistance to L monocytogenesoccurs.
Diagnostic Microbiology Growth of the organism occurs between 20~ and 37~ with fastest growth occurring between 30~ and 37~ A cold enrichment technique may be useful in isolations from contaminated specimens but is of limited value in the 'clinical laboratory. Narrow zones of [3-hemolysis are present around colonies growing on blood agar, but they may be visualized only when the colonies, are picked off the plate. Other characterizing tests for the identification ofL monowtogenes include a positive reaction for catalase, tumbling motility microscopically, and motility in soft agar when grown at room temperature? Cultivation of L rnono~ytogenes is the only reliable means of proving an infection is caused by Listeria. Culture of venous blood, ascitic and other fluids, cervical material, urine, amniotic fluid, lochia, and meconium and tissues at biopsy or autopsy offer the best chances for identifying Listeria in persons with disease. Culture of the stool is not helpful. Feces are positive for Listeria in 1 to 5 percent of healthy adults.
Microscopic examination of the placenta has proven helpful in cases of suspected perinatal infection, revealing infiltration with neutrophils and microabscesses. 2~ Microscopic diagnosis may be attempted by use of Gram stain only in specimens that normally do not contain bacteria (eg, cerebrospinal fluid [CSF], meconium, and placental tissue smears). The finding of short (sometimes coccoid and paired) gram-positive rods strongly supports a diagnosis of listeriosis (Fig 2). L monocytogenes sometimes does not take up Gram stain as well as do other gram-positive organisms. Particularly with long-standing disease or when the patient has received antibiotics, the organisms may appear gram-negative and be confused with Haemophilus infiuenzae when observed in the CSF. In other instances, Listeria has been mistaken for pneumococci and corynebacteria. The submission of clinical specimens for culture may be facilitated by the use of transport-enrichment fluid. It is, however, advisable to submit specimens such as blood, sputum, CSF, and pus without any additives. For patients who have received antibiotics, the use of a commercial antibiotic-removal device in sterile body fluid cultures is useful.
Clinical Manifestations The clinical features of listeriosis have considerable variability and may mimic other infections or other disease states. Based on the most common clinical manifestations, several clinical groups may be distinguished.
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Figure 2. Gram stain of exudate from peritonitis caused by L monocytogenes.Short, grampositive, intracellular organisms with rounded ends are seen arranged irregularly.
Listeriosis During Pregnancy Susceptibility to L monocytogenesis markedly increased in pregnant animals. The predilection of Listeria for the fetoplacental unit and intrauterine infection is well documented. 24,25Maternal listeriosis can be transmitted to the fetus by an ascending or transplacental route. Early gestational listeriosis is associated with septic abortion; however, most cases of perinatal listeriosis are found after the fifth month of pregnancy, with premature delivery of a septic or stillborn infant the result. Evidence of preceding maternal illness often is described when an infant develops early-onset disease. 11,24 Although some symptoms in pregnant women are vague and nonspecific (eg, malaise, myalgia), others are sufficiently distinctive (eg, fever, chills) to alert physicians to a risk for prenatally acquired listeriosis. Blood cultures from such women often are positive for Listeria. Premature labor in pregnant women with listeriosis is common; approximately 70 percent deliver newborns at less than 35 weeks' gestation. The mortality rate, including stillbirth and abortion, is 30 to 50 percent. Early treatment of Listeria sepsis in pregnancy, however, can prevent fetal and neonatal infection and sequelae.~,~
Listeriosis in the Newborn Infant Neonatal listeriosis has become recognized as the most common clinical form of human listeriosis. Infection in the neonatal period usually is divided into two clinical groups defined by age: early- and late-onset infection with onset at 7 days of age or earlier and onset after 7 days of age, respectively. Some clinical and laboratory manifestations of early-onset neonatal listeriosis are outlined in Table 1, which is compiled from clinical cases in which early and late forms of the disease could be differentiated. Classically, early-onset neonatal listeriosis develops within 1 or 2 days of life. However, in one outbreak involving 10 infants with nosocomially acquired listeriosis, an
atypical clinical picture was described. 12 Nine of these infants were bathed shortly after birth with mineral oil contaminated with L monogvtogenes. Clinical features of infection developed 4 to 8 days later and were similar to those seen in late-onset infection, with insidious onset of illness with fever and meningitis being common. Although early-onset disease may occur up to 7 days of age, most cases are clinically apparent at delivery with meconium staining, cyanosis, apnea, respiratory distress, and pneumonia. Meconium-stained liquor is a common feature in such infants Table 1. Features of Early-onset (-<7 Days Old) Neonatal Listeriosis
Feature
PercentAffected
Preterm infant* Mortality overall Mortality (of live-born infants) Features in infants Meconium staining Pneumonia AnemiaS" Thrombocytopenia:~ Meningitis Source of isolate Blood only Maternal features Flu like illnessw Bacteremial]
63 30 15 69 62 62 35 21 73 45 35
*Gestational age <35 weeks. tHemoglobin < 14 g/dL or hematocrit <45. :)Platelets <150 X I09/L. w symptoms, myalgia, and fever from 3 to 30 days before delivery. IlL monocytogenesisolated from blood of mother at any time before delivery of infant.
Neonatal Listeriosis and may occur at any gestational age, even less than 32 weeks. Pneumonia also is common, but radiographic features are not specific, ranging from peribronchial to widespread infiltration. In more long-standing infection, coarse, mottled, or nodular patterns have beeI1 described. Assisted ventilation frequently is necessary in such infants. In spite of ventilatory assistance, persistent hypoxia is seen in severely affected infants. Laboratory features are nonspecific; a leukocytosis with presence of immature cells or, if infection is severe, neutropenia may be seen. Similarly, thrombocytopenia may occur. Many of the infants are anemic, perhaps attributable to hemolysin produced by the organism. These laboratory and clinical features will not distinguish listeriosis from early-onset group B streptococcal or other bacterial infections. In severe infection, a granulomatous rash has been described (Fig 3). Slightly elevated pale patches measuring 1 to 2 mm in diameter with bright erythematous bases are seen. These patches may be difficult to distinguish from other pustular disorders in the neonate. 26 If biopsy specimens are obtained from such areas, a leukocytic infiltrate with multiple bacteria is usually found. Neonatal listerial infection that occurs after 7 days of life is termed late-onset infection. Age at onset often is 12 to 20 days. Two-thirds of affected infants are boys. Although some overlap between early- and late-onset forms of listeriosis occurs, the clinical patterns of the two are usually distinct. Fever is present in 94 percent of infants with late-onset disease, and irritability is present in 75 percent. By far the most common form of Listeria infection during this period is meningitis, which is present in 94 percent of late-onset cases. In many centers, Listeria ranks second only to group B Streptococcus as a cause of bacterial meningitis in this age group, causing approximately 20 percent of such infections. Clinical features do not distinguish listerial meningitis in this age group from other causes. Often, infants do
Figure 3. Rash ofneonatalL mono| infection. Areas of small, elevated, pale pustules surrounded by a deep red erythematous base are seen on the abdomen of a premature infant. (Bortolussi R, Schlech W ]]I: Infectious diseases of the newborn infant, in Remington JS, Klein JO (eds): Listeriosis (ed 4). Philadelphia, PA, Saunders, 1995, p 1064.)
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not appear excessively ill and may, therefore, elude diagnosis for several days. Laboratory features of late-onset infection are not specific. The cell count in CSF usually is high, with a predominance of mature neutrophil and band forms. Occasionally in longstanding disease, a relatively high number of monocytes may be seen. Gram stain of CSF may not always suggest the diagnosis, both because the organism may be rare and because the morphology may be atypical. Mortality of late-onset newborn infection generally is low except if diagnosis is delayed by more than 3 or 4 days after onset of infection. Long-term sequelae and morbidity are uncommon. Among older children or adults with central nervous system Listeria infection, a high incidence of prolonged ataxia, hydrocephalus, and cerebellar atrophy visualized via computed tomography (CT) has been reported. Rhombencephalitis and brain abscess also have been seen and appear to have a good prognosis.25In the course of the septicemic form, an accompanying conjunctivitis sometimes is observed. Other unusual forms oflisteriosis, such as endocarditis and septic arthritis, have been described in adults but appear to be rare in infants.
Therapy Listeria remains susceptible to antibiotics commonly used in its treatment? 7,28 However, the high mortality rate and risk of relapse have prompted a search for newer therapeutic regimens, including quinilones, trimethoprim-sulfamethoxazole, and rifampin. Transferable plasmid-mediated antibiotic resistance has been reported, conferring resistance to chloramphenicol, tetracycline, and erythromycin. Two large in vitro studies of antibiotic susceptibility of human clinical isolates of L rnonocytogenes using broth dilution
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susceptibility methods have been reported. 27,28 Both studies found that the strains represented a homogeneous population, susceptible to ampicillin, penicillin, erythromycin, and tetracycline. As reported in these two studies, the minimal bactericidal concentration (MBC) of antibiotics often is much higher than are levels attainable clinically. Thus, most antibiotics tested are bacteriostatic but not bactericidal. Although bacteriostatic antibiotics have been used in the past, bactericidal antibiotics have a potential advantage for patients with impaired host defense mechanisms, including neonates. Results of cephalosporin antibiotic in vitro and in vivo studies consistently have been disappointing. The organism is uniformly highly resistant to all the cephalosporin antibiotics tested. Several combinations of antibiotics have been comps/red for their bactericidal activity in vivo against L monocytogenes. Because large clinical studies in humans are not available, animal models appear to provide the only practical way to assess therapeutic regimens. Murine models using normal adult or immunodeficient animals have been reported. 29,3~ In an animal model of neonatal listeriosis, the combination of ampicillin with gentamicin gave significantly better eradication of organisms in spleen compared with ampicillin alone. 31 Similarly, the combination of trimethoprim and sulfamethoxazole was superior to either drug alone. Reports of efficacy of other antibiotics in vivo are conflicting. Rifampin has been found by some authors to be highly effective in eradicating organisms, whereas others have found it to be ineffective. Differing sensitivity of strains to rifampin may account for the widely discrepant results. Also, rifampin resistance may develop in vivo when it is used as a single drug. The use of ciprofloxacin in animal models has not suggested any therapeutic advantage over ampicillin. No prospective, antibiotic clinical trials have been reported for L monofytogenes human infection. Anecdotal reports of single cases or reviews of outbreaks support the conclusions drawn from animal models. In one review of the clinical management of 119 cases oflisteriosis from three centers in the United States, excellent therapeutic results were seen for patients treated empirically with penicillin or ampicillin; all had a reduction of fever and clinical improvement.4 However, patients treated initially with cephalosporins had persistent fever and infection. In the largest assessment of treatment regimens during a single outbreak, 32 a lower mortality rate (16% of 57 children) was reported for children given ampicillin compared with those treated with chloramphenicol, tetracycline, or streptomycin (33 percent of 82 children). Nevertheless, in ~the absence of controlled clinical trials, a definitive recommendation for treatment cannot be made.
Suggested Management Listeriosis DuringPregnancy If amnionitis is present, initial treatment should be given by the intravenous route to ensure that adequate tissue levels are achieved: ampicillin, 4 to 6 g/d divided into four equal doses, plus an aminoglycoside. If amnionitis is not present or if acute symptoms of amnionitis have subsided, oral antibiotics probably are adequate: amoxicillin, 2 to 3 g/d divided into four equal
doses. In both situations, treatment should continue for 14 days. If the patient has a significant allergy to ampicillin,therapeutic options are limited. Erythromycin may be given. The estolate form of this drug should be avoided because of increased liver toxicity during pregnancy. Trimethoprim-sulfamethoxazole should not be used because premature delivery of the infant may occur as a consequence of infection, m which case the drug may cause displacement of bilirubin from protein and increase the potential for toxicity in the infant.
Neonatal Listeriosis Ampicillin in combination with an aminoglycoside is the preferred management for early-onset infection. For infants weighing less than or equal to 2,000 g, ampicillin, 100 mg/kg/d divided into two equal doses, should be administered for the first week of life. For infants weighing more than 2,000 g, ampiciliin, 150 mg/kg/d divided into three equal doses, should he administered for the first week of life. For the second week of life and thereafter, the appropriate dosages are 150 mg/kg/d and 200 mg/kg/d for infants weighing less than and more than 2,000 g, respectively. Aminoglycoside doses vary with the agent chosen. For gentamicin, the suggested dosages are 5 mg/kg/day divided into two equal doses for the first week of life, and 7.5 mg/kg/d divided into three equal doses for the second week of life and thereafter. Fourteen days of treatment is recommended for early-onset neonatal sepsis caused byL monocytogenes; however, a 3-week course of treatment should be given in the uncommon event of early-onset neonatal listeriosis with meningitis. Memngitis is common in the late-onset form of neonatal listeriosis and in listeriosis in adults. Delayed eradication of the organism may be seen in such cases. Ampicillin, 200 to 400 mg/kg/d divided into four to six equal doses, in combination with an aminoglycoside for 3 weeks is recommended. 25 Lumbar punctures should be repeated daily until the organism has been cleared. In the event of delayed clearance (more than 2 days of antibiotic therapy), further investigations are indicated and should include CT scan or cranial ultrasound (in infants) to assess for the presence ofcerebritis, abscess, rhombencephalitis, or intracranial hemorrhage. Treatment should be prolonged to 6 weeks if cerebral pathology is identified. If the organism persists in the CSF, the addition of rifampin or trimethoprimsulfamethoxazole may be considered if the organism is sensitive in vitro. Experience with rifampin and trimethoprim-sulfamethoxazole in the neonatal period and with this organism is limited. Cephalosporin antibiotics have no role in treatment because the organism is uniformly resistant. Vancomycin has been used successfully in patients who are allergic to penicillin.21
Prevention Foodborne outbreaks of listeriosis are unpredictable and may occur in a wide geographic area. Therefore, reporting sporadic cases of listeriosis to public health authorities may be the only means of distinguishing sporadic from epidemic disease. The epidemic threshold is unknown and may only be determined in retrospect. The studies suggesting that sporadic listeriosis is also foodborne have important public health implications.
Neonatal Listeriosis
Table 2. Dietary Recommendations for Preventing
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References
Food-borne Listeriosis For all persons 9 Thoroughly cook raw food from animal sources (eg, beef, pork, and poultry). 9 Thoroughly wash raw vegetables before eating. 9 Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods. 9 Avoid consumption of raw (unpasteurized) milk or foods made from raw milk. 9 Wash hands, knives, and cutting boards after handling uncooked foods. Additional recommendations for persons at high risk* 9 Avoid soft cheeses (eg, Mexican-style, feta, Brie, Camembert, and blue-veined cheeses). (There is no need to avoid h a r d cheeses, cream cheese, cottage cheese, or yogurt.) 9 Leftover foods or ready-to-eat foods (eg, hot dogs) should be reheated until steaming hot before eating. 9 Although the risk for listeriosis associated with foods from delicatessen counters is relatively low, pregnant women and immunosuppressed persons may choose to avoid these foods or to thoroughly reheat cold cuts before eating. *Persons immunocompromised by illness or medications, pregnant women, and the elderly. (From the Centers for Disease Control: Update: Foodborne listeriosis United States, 1988-1990. MMWR 41:251, 1992.)
The sampling of foodstuffs associated with sporadic cases of listeriosis is not warranted. In outbreaks, case-control studies to determine potential vehicles of transmission may help define the source, and environmental sampling may be an important part of such outbreak investigations. These clinical a n d environmental isolates should be forwarded to a reference laboratory for appropriate epidemiological typing. At a minimum, serotyping, phage typing, and multifocus enzyme electrophoresis typing should be performed to characterize the epidemic strain. The recognition that b o t h sporadic and outbreak cases of listeriosis are foodborne has led to the development of preventive guidelines by the Centers for Disease Control (Table 2). During an outbreak of listeriosis, high-risk groups, such as pregnant women or those with AIDS, who have a flulike illness should be empirically treated with ampicillin and an aminoglycoside after appropriate cultures of blood, CSF, sputum, rectum, and vagina have been obtained. In pregnant women, amniocentesis for diagnosis of chorioamnionitis may- be appropriate. If membranes have ruptured and contamination is suspected, use of selective media may enhance the isolation of Listeria from these patients. Infection control precautions with gowns, gloves, and careful hand washing will prevent nosocomial transmission between infected infants and is consistent with current procedures for all forms of neonatal sepsis.
Acknowledgments I am grateful for the assistance of Kim Barrett for typing the manuscript and DrJ. Wright for interpreting the histologic slides.
h McLauchlinJ:Listeria monocytogenes, recent advances in the taxonomy and epidemiology of listeriosis in humans.J Appl Bacterio163:1-11, 1987 2. Pirie JHH: Listeria: Change of name for a genus of bacteria. Nature 145:264, 1940 3. Holt JG, Krieg NR, Sheath PHA, et al: Bergey~s Manual of Determinative Bacteriology. Baltimore, MD, Williams & Wilkins, 1994 4. Cherubin CE, Appleman MD, Heseltine PNR, et al: Epidemiologic spectrum and current treatment of listeriosis. Rev Infect Dis 13:1108-1114, 1991 5. ]?inner RW, Schuchat A, Swaninathan B, et al: Role of foods in sporadic iisteriosis: II. Microbiologic and epidemiologic investigations jAMA 267:2046-2050, i992 6. Schlech WF III, Lavigne PM, Bortolussi R, et al: Epidemic listeriosis--evidence for transmission by food. N EnglJ Med 308:203-206, 1983 7. Dalton CB, Austin CC, SobelJ, et al: An outbreak of gastroemeritis and fever due to Listeria monocytogenes in milk. N Engl j Med 336:100-105, 1997 8. Gellin BG, Broome CV, Bibb WF, et al: The epidemiology of iisteri0sis in the United btates--1986. AmJ Epidemiol 133:392-401, 1991 9. Schuchat A, Deaver K, Wenger JD, et al: Role of foods in sporadic listeriosis: I. Case-control study of dietary risk factors. JAMA 267:2041-2045, t992 10. Bojsen-MollerJ: Human listeriosis: Diagnostic, epidemiologic and clinical studie s. Acta Patho! Microbiol Scand 229:1-157, 1992 (suppl) 11. Goulet V, RocourtJ, Rebiere I, et al: Listeriosis outbreak associated with the consumption of rillettes in France in 1993. J Infect Dis 177:155-160, 1998 12. Schuchat A, Eizano C, Broome CV, et al: Outbreak of neonatal listeriosis associated with mineral oil. Pediatr Infect Dis J 10:183189, 1991 13. Alvarez-Domingues C, Vasquez-Boland J-A, Carrasco-Marin E, et al: Host cell heparan sulfate proteoglycans mediate attachment and entry ofListeria monocytogenes, and the listerial surface protein ActA is involved in heparin sulfate receptor recognition. Infect Immun 65:78-88, 1997 14. Southwick FS, Purich DL: Intracellular pathogenesis of listeriosis. N EnglJ Med 334:770-776, 1996 15. Hsieh C-S, Macatonia SE, Tripp CS, et al: Development of Till CD4+ T cells through IL-12 produced by Listeria-induced macrophages. Science 260:547-549, 1993 16. Shen H, MillerJF, Fan X, et al: Compartmentalization of bacterial antigens: Differential effects on priming of CD8 T cells and protective immunity. Cell 92:535-545, 1998 17. Tsukada H, Kawamura I, Arakawa M, et al: Dissociated development of T cells mediating delayed-type hypersensitivity and protective T cells against Listeria mono~togenes and their functional difference in lymphokine production. Infect Immun 59:3589-3595, 1991 18. Buchmeier NA, Schreiber RD: Requirement of endogenous interferon-gamma production for resolution of Listeria monocytogenes infection. Proc Natl Acad Sci USA 82:7404-7408, 1985 19. DesiderioJV, Kiener PA, Lin P-F, et al: Protection of mice against Listeria monocytogenes infection by recombinant human tumor necrosis factor alpha. Infect Immun 57:1615-1617, 1989 20. Topalovski M, Yang S, Boonpasat Y: Listeriosis of the placenta: Clinicopathologic study of seven cases. Am J Obstet Gynecol 169:616-620, 1993 21. Scully RE, Mark EJ, McNeely WF, et al: Weekly Clinicopathological Exercises. N EnglJ Med 336:1439-14~46, 1997
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22. Wilson CB: The ontogeny ofT lymphocyte maturation and function. JPediatr 118:$4-$9, 1991 (suppl) 23. Bortolussi R, Rajaraman K, Serushago B: Role of tumor necrosis factor-alpha and interferon gamma in newborn host defense against Listeria monocvtogenesinfection. Pediatr Res 32:460-464, 1992 24. Ahlfors CE, Goetzman BW, Halstad CC, et ai: Neonatal iisteriosis. AmJ Dis Child 131:405-408, 1977 25. Lorber B: Listeriosis. Clin Infect Dis 24:1-11, 1997 26. Van Praag MCG, Van Rooij RWG, Folkers E, et ah Diagnosis and treatment of pustular disorders in the neonate. Pediatr Dermatol 14:131-143, 1997 27. 2VIacGowanAP, Holt HA, Bywater MJ, et al: In vitro antimicrobial susceptibility ofListeria monocytogenesisolated in the UK and other Listeria species. EurJ Clin Microbiol Infect Dis 9:767-770, 1990 28. Wiggins GL, Albritton WL, FeeleyJC: Antibiotic susceptibility of
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clinical isolates of Listeria mo~ocytogenes. Antimicrob Agents Chemother I3:854-860, 1978 Hof P, Emmerling P, Seeliger tlPR: Murine model for therapy of iisteriosis in the compromised host. Chemotherapy 27:214-219, 1981 Bakker-Woudenberg IAJM, de Bos P, van Leeuwen WB, et al: Efficacy of ampicillin therapy in experimental listeriosis in mice with impaired T-cell-mediated immune response. Antimicrob Agents Chemother 19:76-81, 1981 Hawkins AE, Bortolussi R, Issekutz AC: In vitro and in vivo actMty ofvarious antibiotics against Listeria mono~togenes type 4b. Clin Invest Med 7:335-341, i984 Weingartner L, Ortel S: Zur Behandlung der Listeriose mit Ampicillin. Dtsch Med Wochenschr 92:1098, 1967
L
isteria monocytogenes is a short, motile, gram-positive, non-
spore-forming bacillus that has been isolated from a variety of animal species in association with disease, l The history of the organism was summarized by McLauchlin 1 in 1987. Listeria was first described in 1926 by Murray, Webb, and Swann, who discovered it while investigating an epidemic of infection among laboratory rabbits and guinea pigs. At that time, it was given the name Bacterium monocytogenes because infection in the animals was characterized by monocytosis. Three years later, Nyfeldt isolated B monocytogcnesfrom the blood of a patient with an infectious mononucleosis-like disease. It was not until 1936 that the first human perinatal infection was documented. The name of the organism was changed to Listeria monocytogenes in 1940. 2 Six serovars o f L monocytogenes have been described and are distinguished on the basis of somatic O and flagellar H anti-
From the Departments of _Pediatrics and Microbiology and Immunology, Dalhousie University,Halifax, Nova Scotia, Canada. Address correspondenceto RobertBortolussi,M_D,FRCPC, 1WK GraceHealth Centre,5850 UniversityAve, Halifax, NS, CanadaB3J 3G9. Copy@t 9 1999 by W.B. Saunders Company 1045-1870/99/1002-0007510.00/0
gens. 3 Serovars 1/2a, 4a, and 4b are the most common isolates from animals and humans with clinical disease. In the United States, serovars 4b and 1/2a account for 95 percent of strains, with serotype 4b being the most common overall. Other serovars originate from soil or other environmental sources but rarely are seen as clinical pathogens.
Epidemiology Recent evidence suggests that most, if not all, human cases of L
monoqytogenes are acquired through ingestion of contaminated food.4,5 The first outbreak that convincingly showed transmission via a foodborne source was reported from the Atlantic Maritime provinces of Canada. 6 Several outbreaks have been attributed to consumption of inadequately pasteurized dairy products. 7,s However, when properly conducted, pasteurization should eliminate Listeria. The improved ability to culture L monocytogeneswith selective media has provided an opportunity to examine specific foods in nonepidemic cases of listeriosis. Epidemiological and microbiological investigations of patients and foods present in the homes of these patients have produced increasing evidence pointing to the important role of food in transmission of these sporadic
Seminars in Pediatric I@ctious Diseases, Vo110, No 2 (April), 1999:pp 111-118
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cases of listeriosis.5'9'm Although L monog;togenes is isolated frequently from foods, contaminated foods likely to cause listeriosis are characterized as ready-to-eat foods, foods containing higher concentrations ofL monocytogenes, and foods containing serotype 4b. These studies implicated undercooked chicken and soft cheeses as significant sources of disease and are supported by sampling surveys conducted by regulatory agencies. Active surveillance in the United States suggests an annual incidence of 0.7 cases per 100,000 population.8 Approximately 1,700 cases of listeriosis occur annually in the United States, with a mortality rate of 40 percent. Slightly lower figures have been reported recently from Europe. For neonatal llsteriosis, the incidence in the United States is approximately 13 cases per 100,000 live births, 30 percent of the total number of cases of reported listeriosis. Similar incidence rates have been reported in studies from Europe. Of interest, epidemics of foodborne listeriosis have disproportionately involved perinatal cases.8,H No differences in carriage rates between pregnant women and nonpregnant individuals have been found in fecal and vaginal specimens. The possibilitythat a lower infective dose is needed to cause disease in pregnant women and immunocompromised patients has been proposed but not confirmed. The risk of listeriosis varies among segments of the population. Two thirds of cases of llsteriosis in adults occur in immunocompromised patients. Renal transplantation appears to be a particularly- significant risk factor. Listeriosis also is reported in patients with AIDS, who have a 1,000-fold risk of acquiring invasive Iisteriosis. Although most large outbreaks ofllsteriosis have occurred in the community, case clusters of nosocomial listeriosis in both newborn infants and adults have been described. The index case in one nosocomial outbreak was diagnosed as "early-onset" newborn infection (within 1 week of birth). 12 In this outbreak, the index case was not symptomatic at birth and was bathed with mineral oil that then became contaminated with the epidemic isolate. Subsequent bathing of other infants with the same oil led to "late-onset" disease in other infants.
Pathogenicity Because L monocytogenes is a low-grade intracellular pathogen, it has been used extensively in animal models to gain an understanding of the cell-mediated immune syst)m. Microbial attachment to host cells is the initial step in cell invasion. Recent work has shown that interaction with a heparan sulfate peptidoglycan receptor on the surface of cells is involved in L mono~ytogenes adhesion.IS A family of surface proteins known as internalins are secreted in large amounts by all strains of Listeria capable of invading host cells. Although these proteins may identify an important factor associated with entrance into epithelial cells and hepatocytes, they do not explain intracellular spread and multiplication. The intracellular survival of Listeria also requires synthesis of a specific hemolysin, termed llsteriolysin O, which lyses the phagosomal membrane. Release ofL monocytogenesfrom intracellular vacuoles precipitates both intracellular growth and polymerization of actin of the host cell around Listeria. Actin
polymerization is important in the cell-to-cell transfer of L mono~togenes and is encoded by the ActA gene. 14 The liberated organism thrives in the cytoplasm, which provides better growth conditions. Through these mechanisms, Listeria can enter, grow, and spread inside a wide variety of cells, including renal epithelial cells, fibroblasts, vascular endothelium, hepatocftes, and enterocytes. By producing ActA, Listeria causes host-cell actin to assemble into filaments at one end of the bacterium. This "rocket tail" provides the propulsive force for the organism to move through the cytoplasm (Fig 1). When the bacteria reachthe cell membrane, they form filipods that enter adjacent cells. The process leading to acquired immunity to Listeria is now clearer. In immunocompetent adults, Listena is phagocytosed by both "professional" phagocytes (macrophages, monocytes) and "nonprofessional" phagocytic cells (fibroblasts, hepatocytes). Macrophages take up and process llsterial proteins and produce interleukin (IL)- 12 and IL- 1.15Peptides resulting from digestion of Listeria are actively processed by the macrophage in the endoplasmic reticulum, where the peptides bind to major histocompatibility complex (MI-IC) class I moleculesJ 6 The Listeria-peptide-MHC complex is transported to the cell surface, where it is recognized by cytotoxic T cells (CD8 phenotype) and helper T ceils (T~). In the presence of IG12, naive TH cells, differentiate into TH-1 cells, which proliferate and produce IL-2, 9 15Interleukin-12 also stimuinterferon (IFN)-',/, and lymph otoxm. lates activation and proliferation of natural killer (NK) cells. Both cell clones produce IFN-% Cytotoxic T cells interact with cells bearing L mono~togenes antigens, causing them to lyse. Natural killer cells are further stimulated by WN-',/, inducing an enhanced ability of these cells to lyse infected fibroblasts and hepatocytes. Peak immunity to Listeria is expressed about the sixth day of infection, which coincides with maximal T-cell synthesis of IFN-% 17,m Macrophage colony-stimulating factor (M-CSF) and tumor necrosis factor (TNF)-ot also appear during the first 5 days and have been implicated as mediators oflisterial clearance. TNF-ct enhances a variety of antibacterial or antiparasitic resistance mechanisms. Monocytes and macrophages probably are the most abundant source of TNF-a. Endotoxin (LPS) and other agents, including mitogens, viruses, and cytokines such as M-CSF, K-l, IL-2, and IFN-% have been identified as inducers of TNF-ot. When administered before infection, TNF-et inducers enhance resistance of the host to bacterial infection. TNF-ot produced endogenously during sublethal Listeria infection in adult animals appears to function as an inducer of resistanc@ 9 suggesting that TNF-et-dependent mechanisms limit intracellular infection early in the course. The pathogenesis of fetal listeriosis is not understood as clearly. Because the heaviest loci for neonatal infection are the lungs and gut, probably the fetus is infected by swallowing contaminated liquor, as well as through the transplacental hematogenous route. 2~ An ascending pathway from the lower genital tract may occur, but infection via the transplacental route is favored by most experts. L mono~togenes chorioamnionitis diagnosed by transabdorninal amniocentesis (free from vaginal bacterial contamination) has been reported and, thus, indicates a maternal-to-newborn blood-borne route of infection. In newborn animals, susceptibilityto Listeria is increased and is associated with delayed activation of macrophages. Studies on the afferent and efferent arms of the immune system in
NeonatalListeriosis
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II
Figure
1. Electron micrograph of a cell containing several ingested organisms. In several (arrows), the organism appears to have escaped into the cytosome of the cell with formation of a "rocket tail" of the organism. The solid bar represents approximately
1/xm. newborn mice have shown that macrophage-T-lymphocyte interaction is impaired, a n d macrophage activation does not occur.22 TNF-e~ is decreased among newborn rats challenged with L monocytogenes, in which TNF-e~ was detected only among animals older than 8 days. 23 The age at which TNF-e~ becomes measurable corresponds to the approximate age at which increased resistance to L monocytogenesoccurs.
Diagnostic Microbiology Growth of the organism occurs between 20~ and 37~ with fastest growth occurring between 30~ and 37~ A cold enrichment technique may be useful in isolations from contaminated specimens but is of limited value in the 'clinical laboratory. Narrow zones of [3-hemolysis are present around colonies growing on blood agar, but they may be visualized only when the colonies, are picked off the plate. Other characterizing tests for the identification ofL monowtogenes include a positive reaction for catalase, tumbling motility microscopically, and motility in soft agar when grown at room temperature? Cultivation of L rnono~ytogenes is the only reliable means of proving an infection is caused by Listeria. Culture of venous blood, ascitic and other fluids, cervical material, urine, amniotic fluid, lochia, and meconium and tissues at biopsy or autopsy offer the best chances for identifying Listeria in persons with disease. Culture of the stool is not helpful. Feces are positive for Listeria in 1 to 5 percent of healthy adults.
Microscopic examination of the placenta has proven helpful in cases of suspected perinatal infection, revealing infiltration with neutrophils and microabscesses. 2~ Microscopic diagnosis may be attempted by use of Gram stain only in specimens that normally do not contain bacteria (eg, cerebrospinal fluid [CSF], meconium, and placental tissue smears). The finding of short (sometimes coccoid and paired) gram-positive rods strongly supports a diagnosis of listeriosis (Fig 2). L monocytogenes sometimes does not take up Gram stain as well as do other gram-positive organisms. Particularly with long-standing disease or when the patient has received antibiotics, the organisms may appear gram-negative and be confused with Haemophilus infiuenzae when observed in the CSF. In other instances, Listeria has been mistaken for pneumococci and corynebacteria. The submission of clinical specimens for culture may be facilitated by the use of transport-enrichment fluid. It is, however, advisable to submit specimens such as blood, sputum, CSF, and pus without any additives. For patients who have received antibiotics, the use of a commercial antibiotic-removal device in sterile body fluid cultures is useful.
Clinical Manifestations The clinical features of listeriosis have considerable variability and may mimic other infections or other disease states. Based on the most common clinical manifestations, several clinical groups may be distinguished.
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RobertBortolussi
Figure 2. Gram stain of exudate from peritonitis caused by L monocytogenes.Short, grampositive, intracellular organisms with rounded ends are seen arranged irregularly.
Listeriosis During Pregnancy Susceptibility to L monocytogenesis markedly increased in pregnant animals. The predilection of Listeria for the fetoplacental unit and intrauterine infection is well documented. 24,25Maternal listeriosis can be transmitted to the fetus by an ascending or transplacental route. Early gestational listeriosis is associated with septic abortion; however, most cases of perinatal listeriosis are found after the fifth month of pregnancy, with premature delivery of a septic or stillborn infant the result. Evidence of preceding maternal illness often is described when an infant develops early-onset disease. 11,24 Although some symptoms in pregnant women are vague and nonspecific (eg, malaise, myalgia), others are sufficiently distinctive (eg, fever, chills) to alert physicians to a risk for prenatally acquired listeriosis. Blood cultures from such women often are positive for Listeria. Premature labor in pregnant women with listeriosis is common; approximately 70 percent deliver newborns at less than 35 weeks' gestation. The mortality rate, including stillbirth and abortion, is 30 to 50 percent. Early treatment of Listeria sepsis in pregnancy, however, can prevent fetal and neonatal infection and sequelae.~,~
Listeriosis in the Newborn Infant Neonatal listeriosis has become recognized as the most common clinical form of human listeriosis. Infection in the neonatal period usually is divided into two clinical groups defined by age: early- and late-onset infection with onset at 7 days of age or earlier and onset after 7 days of age, respectively. Some clinical and laboratory manifestations of early-onset neonatal listeriosis are outlined in Table 1, which is compiled from clinical cases in which early and late forms of the disease could be differentiated. Classically, early-onset neonatal listeriosis develops within 1 or 2 days of life. However, in one outbreak involving 10 infants with nosocomially acquired listeriosis, an
atypical clinical picture was described. 12 Nine of these infants were bathed shortly after birth with mineral oil contaminated with L monogvtogenes. Clinical features of infection developed 4 to 8 days later and were similar to those seen in late-onset infection, with insidious onset of illness with fever and meningitis being common. Although early-onset disease may occur up to 7 days of age, most cases are clinically apparent at delivery with meconium staining, cyanosis, apnea, respiratory distress, and pneumonia. Meconium-stained liquor is a common feature in such infants Table 1. Features of Early-onset (-<7 Days Old) Neonatal Listeriosis
Feature
PercentAffected
Preterm infant* Mortality overall Mortality (of live-born infants) Features in infants Meconium staining Pneumonia AnemiaS" Thrombocytopenia:~ Meningitis Source of isolate Blood only Maternal features Flu like illnessw Bacteremial]
63 30 15 69 62 62 35 21 73 45 35
*Gestational age <35 weeks. tHemoglobin < 14 g/dL or hematocrit <45. :)Platelets <150 X I09/L. w symptoms, myalgia, and fever from 3 to 30 days before delivery. IlL monocytogenesisolated from blood of mother at any time before delivery of infant.
Neonatal Listeriosis and may occur at any gestational age, even less than 32 weeks. Pneumonia also is common, but radiographic features are not specific, ranging from peribronchial to widespread infiltration. In more long-standing infection, coarse, mottled, or nodular patterns have beeI1 described. Assisted ventilation frequently is necessary in such infants. In spite of ventilatory assistance, persistent hypoxia is seen in severely affected infants. Laboratory features are nonspecific; a leukocytosis with presence of immature cells or, if infection is severe, neutropenia may be seen. Similarly, thrombocytopenia may occur. Many of the infants are anemic, perhaps attributable to hemolysin produced by the organism. These laboratory and clinical features will not distinguish listeriosis from early-onset group B streptococcal or other bacterial infections. In severe infection, a granulomatous rash has been described (Fig 3). Slightly elevated pale patches measuring 1 to 2 mm in diameter with bright erythematous bases are seen. These patches may be difficult to distinguish from other pustular disorders in the neonate. 26 If biopsy specimens are obtained from such areas, a leukocytic infiltrate with multiple bacteria is usually found. Neonatal listerial infection that occurs after 7 days of life is termed late-onset infection. Age at onset often is 12 to 20 days. Two-thirds of affected infants are boys. Although some overlap between early- and late-onset forms of listeriosis occurs, the clinical patterns of the two are usually distinct. Fever is present in 94 percent of infants with late-onset disease, and irritability is present in 75 percent. By far the most common form of Listeria infection during this period is meningitis, which is present in 94 percent of late-onset cases. In many centers, Listeria ranks second only to group B Streptococcus as a cause of bacterial meningitis in this age group, causing approximately 20 percent of such infections. Clinical features do not distinguish listerial meningitis in this age group from other causes. Often, infants do
Figure 3. Rash ofneonatalL mono| infection. Areas of small, elevated, pale pustules surrounded by a deep red erythematous base are seen on the abdomen of a premature infant. (Bortolussi R, Schlech W ]]I: Infectious diseases of the newborn infant, in Remington JS, Klein JO (eds): Listeriosis (ed 4). Philadelphia, PA, Saunders, 1995, p 1064.)
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not appear excessively ill and may, therefore, elude diagnosis for several days. Laboratory features of late-onset infection are not specific. The cell count in CSF usually is high, with a predominance of mature neutrophil and band forms. Occasionally in longstanding disease, a relatively high number of monocytes may be seen. Gram stain of CSF may not always suggest the diagnosis, both because the organism may be rare and because the morphology may be atypical. Mortality of late-onset newborn infection generally is low except if diagnosis is delayed by more than 3 or 4 days after onset of infection. Long-term sequelae and morbidity are uncommon. Among older children or adults with central nervous system Listeria infection, a high incidence of prolonged ataxia, hydrocephalus, and cerebellar atrophy visualized via computed tomography (CT) has been reported. Rhombencephalitis and brain abscess also have been seen and appear to have a good prognosis.25In the course of the septicemic form, an accompanying conjunctivitis sometimes is observed. Other unusual forms oflisteriosis, such as endocarditis and septic arthritis, have been described in adults but appear to be rare in infants.
Therapy Listeria remains susceptible to antibiotics commonly used in its treatment? 7,28 However, the high mortality rate and risk of relapse have prompted a search for newer therapeutic regimens, including quinilones, trimethoprim-sulfamethoxazole, and rifampin. Transferable plasmid-mediated antibiotic resistance has been reported, conferring resistance to chloramphenicol, tetracycline, and erythromycin. Two large in vitro studies of antibiotic susceptibility of human clinical isolates of L rnonocytogenes using broth dilution
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susceptibility methods have been reported. 27,28 Both studies found that the strains represented a homogeneous population, susceptible to ampicillin, penicillin, erythromycin, and tetracycline. As reported in these two studies, the minimal bactericidal concentration (MBC) of antibiotics often is much higher than are levels attainable clinically. Thus, most antibiotics tested are bacteriostatic but not bactericidal. Although bacteriostatic antibiotics have been used in the past, bactericidal antibiotics have a potential advantage for patients with impaired host defense mechanisms, including neonates. Results of cephalosporin antibiotic in vitro and in vivo studies consistently have been disappointing. The organism is uniformly highly resistant to all the cephalosporin antibiotics tested. Several combinations of antibiotics have been comps/red for their bactericidal activity in vivo against L monocytogenes. Because large clinical studies in humans are not available, animal models appear to provide the only practical way to assess therapeutic regimens. Murine models using normal adult or immunodeficient animals have been reported. 29,3~ In an animal model of neonatal listeriosis, the combination of ampicillin with gentamicin gave significantly better eradication of organisms in spleen compared with ampicillin alone. 31 Similarly, the combination of trimethoprim and sulfamethoxazole was superior to either drug alone. Reports of efficacy of other antibiotics in vivo are conflicting. Rifampin has been found by some authors to be highly effective in eradicating organisms, whereas others have found it to be ineffective. Differing sensitivity of strains to rifampin may account for the widely discrepant results. Also, rifampin resistance may develop in vivo when it is used as a single drug. The use of ciprofloxacin in animal models has not suggested any therapeutic advantage over ampicillin. No prospective, antibiotic clinical trials have been reported for L monofytogenes human infection. Anecdotal reports of single cases or reviews of outbreaks support the conclusions drawn from animal models. In one review of the clinical management of 119 cases oflisteriosis from three centers in the United States, excellent therapeutic results were seen for patients treated empirically with penicillin or ampicillin; all had a reduction of fever and clinical improvement.4 However, patients treated initially with cephalosporins had persistent fever and infection. In the largest assessment of treatment regimens during a single outbreak, 32 a lower mortality rate (16% of 57 children) was reported for children given ampicillin compared with those treated with chloramphenicol, tetracycline, or streptomycin (33 percent of 82 children). Nevertheless, in ~the absence of controlled clinical trials, a definitive recommendation for treatment cannot be made.
Suggested Management Listeriosis DuringPregnancy If amnionitis is present, initial treatment should be given by the intravenous route to ensure that adequate tissue levels are achieved: ampicillin, 4 to 6 g/d divided into four equal doses, plus an aminoglycoside. If amnionitis is not present or if acute symptoms of amnionitis have subsided, oral antibiotics probably are adequate: amoxicillin, 2 to 3 g/d divided into four equal
doses. In both situations, treatment should continue for 14 days. If the patient has a significant allergy to ampicillin,therapeutic options are limited. Erythromycin may be given. The estolate form of this drug should be avoided because of increased liver toxicity during pregnancy. Trimethoprim-sulfamethoxazole should not be used because premature delivery of the infant may occur as a consequence of infection, m which case the drug may cause displacement of bilirubin from protein and increase the potential for toxicity in the infant.
Neonatal Listeriosis Ampicillin in combination with an aminoglycoside is the preferred management for early-onset infection. For infants weighing less than or equal to 2,000 g, ampicillin, 100 mg/kg/d divided into two equal doses, should be administered for the first week of life. For infants weighing more than 2,000 g, ampiciliin, 150 mg/kg/d divided into three equal doses, should he administered for the first week of life. For the second week of life and thereafter, the appropriate dosages are 150 mg/kg/d and 200 mg/kg/d for infants weighing less than and more than 2,000 g, respectively. Aminoglycoside doses vary with the agent chosen. For gentamicin, the suggested dosages are 5 mg/kg/day divided into two equal doses for the first week of life, and 7.5 mg/kg/d divided into three equal doses for the second week of life and thereafter. Fourteen days of treatment is recommended for early-onset neonatal sepsis caused byL monocytogenes; however, a 3-week course of treatment should be given in the uncommon event of early-onset neonatal listeriosis with meningitis. Memngitis is common in the late-onset form of neonatal listeriosis and in listeriosis in adults. Delayed eradication of the organism may be seen in such cases. Ampicillin, 200 to 400 mg/kg/d divided into four to six equal doses, in combination with an aminoglycoside for 3 weeks is recommended. 25 Lumbar punctures should be repeated daily until the organism has been cleared. In the event of delayed clearance (more than 2 days of antibiotic therapy), further investigations are indicated and should include CT scan or cranial ultrasound (in infants) to assess for the presence ofcerebritis, abscess, rhombencephalitis, or intracranial hemorrhage. Treatment should be prolonged to 6 weeks if cerebral pathology is identified. If the organism persists in the CSF, the addition of rifampin or trimethoprimsulfamethoxazole may be considered if the organism is sensitive in vitro. Experience with rifampin and trimethoprim-sulfamethoxazole in the neonatal period and with this organism is limited. Cephalosporin antibiotics have no role in treatment because the organism is uniformly resistant. Vancomycin has been used successfully in patients who are allergic to penicillin.21
Prevention Foodborne outbreaks of listeriosis are unpredictable and may occur in a wide geographic area. Therefore, reporting sporadic cases of listeriosis to public health authorities may be the only means of distinguishing sporadic from epidemic disease. The epidemic threshold is unknown and may only be determined in retrospect. The studies suggesting that sporadic listeriosis is also foodborne have important public health implications.
Neonatal Listeriosis
Table 2. Dietary Recommendations for Preventing
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References
Food-borne Listeriosis For all persons 9 Thoroughly cook raw food from animal sources (eg, beef, pork, and poultry). 9 Thoroughly wash raw vegetables before eating. 9 Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods. 9 Avoid consumption of raw (unpasteurized) milk or foods made from raw milk. 9 Wash hands, knives, and cutting boards after handling uncooked foods. Additional recommendations for persons at high risk* 9 Avoid soft cheeses (eg, Mexican-style, feta, Brie, Camembert, and blue-veined cheeses). (There is no need to avoid h a r d cheeses, cream cheese, cottage cheese, or yogurt.) 9 Leftover foods or ready-to-eat foods (eg, hot dogs) should be reheated until steaming hot before eating. 9 Although the risk for listeriosis associated with foods from delicatessen counters is relatively low, pregnant women and immunosuppressed persons may choose to avoid these foods or to thoroughly reheat cold cuts before eating. *Persons immunocompromised by illness or medications, pregnant women, and the elderly. (From the Centers for Disease Control: Update: Foodborne listeriosis United States, 1988-1990. MMWR 41:251, 1992.)
The sampling of foodstuffs associated with sporadic cases of listeriosis is not warranted. In outbreaks, case-control studies to determine potential vehicles of transmission may help define the source, and environmental sampling may be an important part of such outbreak investigations. These clinical a n d environmental isolates should be forwarded to a reference laboratory for appropriate epidemiological typing. At a minimum, serotyping, phage typing, and multifocus enzyme electrophoresis typing should be performed to characterize the epidemic strain. The recognition that b o t h sporadic and outbreak cases of listeriosis are foodborne has led to the development of preventive guidelines by the Centers for Disease Control (Table 2). During an outbreak of listeriosis, high-risk groups, such as pregnant women or those with AIDS, who have a flulike illness should be empirically treated with ampicillin and an aminoglycoside after appropriate cultures of blood, CSF, sputum, rectum, and vagina have been obtained. In pregnant women, amniocentesis for diagnosis of chorioamnionitis may- be appropriate. If membranes have ruptured and contamination is suspected, use of selective media may enhance the isolation of Listeria from these patients. Infection control precautions with gowns, gloves, and careful hand washing will prevent nosocomial transmission between infected infants and is consistent with current procedures for all forms of neonatal sepsis.
Acknowledgments I am grateful for the assistance of Kim Barrett for typing the manuscript and DrJ. Wright for interpreting the histologic slides.
h McLauchlinJ:Listeria monocytogenes, recent advances in the taxonomy and epidemiology of listeriosis in humans.J Appl Bacterio163:1-11, 1987 2. Pirie JHH: Listeria: Change of name for a genus of bacteria. Nature 145:264, 1940 3. Holt JG, Krieg NR, Sheath PHA, et al: Bergey~s Manual of Determinative Bacteriology. Baltimore, MD, Williams & Wilkins, 1994 4. Cherubin CE, Appleman MD, Heseltine PNR, et al: Epidemiologic spectrum and current treatment of listeriosis. Rev Infect Dis 13:1108-1114, 1991 5. ]?inner RW, Schuchat A, Swaninathan B, et al: Role of foods in sporadic iisteriosis: II. Microbiologic and epidemiologic investigations jAMA 267:2046-2050, i992 6. Schlech WF III, Lavigne PM, Bortolussi R, et al: Epidemic listeriosis--evidence for transmission by food. N EnglJ Med 308:203-206, 1983 7. Dalton CB, Austin CC, SobelJ, et al: An outbreak of gastroemeritis and fever due to Listeria monocytogenes in milk. N Engl j Med 336:100-105, 1997 8. Gellin BG, Broome CV, Bibb WF, et al: The epidemiology of iisteri0sis in the United btates--1986. AmJ Epidemiol 133:392-401, 1991 9. Schuchat A, Deaver K, Wenger JD, et al: Role of foods in sporadic listeriosis: I. Case-control study of dietary risk factors. JAMA 267:2041-2045, t992 10. Bojsen-MollerJ: Human listeriosis: Diagnostic, epidemiologic and clinical studie s. Acta Patho! Microbiol Scand 229:1-157, 1992 (suppl) 11. Goulet V, RocourtJ, Rebiere I, et al: Listeriosis outbreak associated with the consumption of rillettes in France in 1993. J Infect Dis 177:155-160, 1998 12. Schuchat A, Eizano C, Broome CV, et al: Outbreak of neonatal listeriosis associated with mineral oil. Pediatr Infect Dis J 10:183189, 1991 13. Alvarez-Domingues C, Vasquez-Boland J-A, Carrasco-Marin E, et al: Host cell heparan sulfate proteoglycans mediate attachment and entry ofListeria monocytogenes, and the listerial surface protein ActA is involved in heparin sulfate receptor recognition. Infect Immun 65:78-88, 1997 14. Southwick FS, Purich DL: Intracellular pathogenesis of listeriosis. N EnglJ Med 334:770-776, 1996 15. Hsieh C-S, Macatonia SE, Tripp CS, et al: Development of Till CD4+ T cells through IL-12 produced by Listeria-induced macrophages. Science 260:547-549, 1993 16. Shen H, MillerJF, Fan X, et al: Compartmentalization of bacterial antigens: Differential effects on priming of CD8 T cells and protective immunity. Cell 92:535-545, 1998 17. Tsukada H, Kawamura I, Arakawa M, et al: Dissociated development of T cells mediating delayed-type hypersensitivity and protective T cells against Listeria mono~togenes and their functional difference in lymphokine production. Infect Immun 59:3589-3595, 1991 18. Buchmeier NA, Schreiber RD: Requirement of endogenous interferon-gamma production for resolution of Listeria monocytogenes infection. Proc Natl Acad Sci USA 82:7404-7408, 1985 19. DesiderioJV, Kiener PA, Lin P-F, et al: Protection of mice against Listeria monocytogenes infection by recombinant human tumor necrosis factor alpha. Infect Immun 57:1615-1617, 1989 20. Topalovski M, Yang S, Boonpasat Y: Listeriosis of the placenta: Clinicopathologic study of seven cases. Am J Obstet Gynecol 169:616-620, 1993 21. Scully RE, Mark EJ, McNeely WF, et al: Weekly Clinicopathological Exercises. N EnglJ Med 336:1439-14~46, 1997
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22. Wilson CB: The ontogeny ofT lymphocyte maturation and function. JPediatr 118:$4-$9, 1991 (suppl) 23. Bortolussi R, Rajaraman K, Serushago B: Role of tumor necrosis factor-alpha and interferon gamma in newborn host defense against Listeria monocvtogenesinfection. Pediatr Res 32:460-464, 1992 24. Ahlfors CE, Goetzman BW, Halstad CC, et ai: Neonatal iisteriosis. AmJ Dis Child 131:405-408, 1977 25. Lorber B: Listeriosis. Clin Infect Dis 24:1-11, 1997 26. Van Praag MCG, Van Rooij RWG, Folkers E, et ah Diagnosis and treatment of pustular disorders in the neonate. Pediatr Dermatol 14:131-143, 1997 27. 2VIacGowanAP, Holt HA, Bywater MJ, et al: In vitro antimicrobial susceptibility ofListeria monocytogenesisolated in the UK and other Listeria species. EurJ Clin Microbiol Infect Dis 9:767-770, 1990 28. Wiggins GL, Albritton WL, FeeleyJC: Antibiotic susceptibility of
29.
30.
31.
32.
clinical isolates of Listeria mo~ocytogenes. Antimicrob Agents Chemother I3:854-860, 1978 Hof P, Emmerling P, Seeliger tlPR: Murine model for therapy of iisteriosis in the compromised host. Chemotherapy 27:214-219, 1981 Bakker-Woudenberg IAJM, de Bos P, van Leeuwen WB, et al: Efficacy of ampicillin therapy in experimental listeriosis in mice with impaired T-cell-mediated immune response. Antimicrob Agents Chemother 19:76-81, 1981 Hawkins AE, Bortolussi R, Issekutz AC: In vitro and in vivo actMty ofvarious antibiotics against Listeria mono~togenes type 4b. Clin Invest Med 7:335-341, i984 Weingartner L, Ortel S: Zur Behandlung der Listeriose mit Ampicillin. Dtsch Med Wochenschr 92:1098, 1967