Version May 2024
INTRODUCTION — Listeria monocytogenes is an important bacterial pathogen in neonates, immunosuppressed patients, older adults, pregnant women, and, occasionally, previously healthy individuals.
The clinical manifestations and diagnosis of listerial infection will be reviewed here. The treatment, prognosis, and prevention of listerial infection and the epidemiology and pathogenesis of listerial infection are discussed separately. (See "Treatment and prevention of Listeria monocytogenes infection" and "Epidemiology and pathogenesis of Listeria monocytogenes infection".)
INDIVIDUALS AT HIGHEST RISK — L. monocytogenes causes invasive disease including meningitis, meningoencephalitis, and bacteremia in susceptible patients, such as immunosuppressed patients, individuals at the extremes of age (neonates and older adults), and pregnant women. A number of diseases and medications are risk factors for Listeria infection; these are discussed separately. Listeria is also a cause of self-limited febrile gastroenteritis in normal hosts who ingest high numbers of organisms [1]. (See "Epidemiology and pathogenesis of Listeria monocytogenes infection", section on 'Clinical epidemiology'.)
The importance of age was illustrated in a four-state, multicenter survey of bacterial meningitis in the United States in 1995 [2]. Listeria accounted for 22 percent of cases in older adults, 23 percent in neonates, and only 4 percent between the ages of 2 and 60.
MICROBIOLOGY — Listeria is a short gram-positive rod that occurs singly or in short chains. However, the identification of Listeria on Gram stain may be challenging. Listeria may resemble pneumococci (diplococci) or diphtheroids (Corynebacteria) or be gram variable and confused with Haemophilus species (picture 1) [3-5]. Thus, the possibility of Listeria should always be considered when "diphtheroids" are reported to be growing from blood or CSF cultures.
Listeria is aerobic and facultatively anaerobic and grows well at refrigeration temperatures (4° to 10°C). Rarely, the "cold enrichment" technique and selective media are used when attempting to isolate Listeria from mixed cultures, such as stool [6]. Listeria produces a characteristic appearance on blood agar with small zones of clear beta-hemolysis around each colony (picture 2). They are motile and non-spore-forming and exhibit characteristic tumbling motility by light microscopy (picture 3 and movie 1) [5,6].
L. monocytogenes is the only Listeria species that regularly infects humans, although rare cases of human infections with Listeria ivanovii (a pathogen of ruminants) and Listeria grayi have been reported [7,8].
NONPREGNANT PATIENTS
Gastroenteritis — Listeria accounts for less than 1 percent of reported cases of bacterial foodborne infections overall [9,10]. Outbreaks of Listeria febrile gastroenteritis from contaminated food are not uncommonly reported [1,11,12]. (See "Epidemiology and pathogenesis of Listeria monocytogenes infection", section on 'Food epidemiology and outbreaks'.)
The attack rate in various outbreaks of gastroenteritis varied from 50 to 100 percent [1]. Listeria infection is more common in the summer.
Clinical features — Febrile gastroenteritis secondary to listerial infection typically occurs after ingestion of a large inoculum of bacteria from contaminated food and can occur in otherwise healthy hosts [1]. The incubation period for Listeria gastroenteritis is substantially shorter than the incubation period for invasive disease [1,13,14]. For gastroenteritis, the mean incubation period is 24 hours (range 6 hours to 10 days) [1].
Similar to other causes of acute foodborne infectious diarrheal disease, common symptoms include fever, watery diarrhea, nausea, vomiting, headache, and pains in joints and muscles. The typical duration of symptoms is two days or less, and recovery is generally complete [1].
Invasive infection as a sequela of listerial gastroenteritis seems to be rare; the risk is greatest in immunocompromised, pregnant, or older adult patients [1]. (See 'Invasive disease' below.)
Diagnosis — Listeriosis should be suspected in patients with presumptive Listeria exposure (table 1) and relevant symptoms (including myalgia, abdominal or back pain, nausea, vomiting, or diarrhea), with or without fever ≥38.1°C (100.6°F) [15]. The diagnosis of Listeria as a cause of febrile gastroenteritis is often not entertained as patients may not seek medical attention, and symptoms resolve within a short period of time.
Stool studies should be obtained to evaluate for common alternative causes of diarrheal illness, including routine stool culture (or multiplex polymerase chain reaction [PCR] in centers where available) and testing for detection of Clostridioides difficile (see 'Differential diagnosis' below). In addition, blood cultures should be obtained for patients who are febrile and/or immunocompromised.
In the absence of bacteremia, it is difficult to establish a definitive diagnosis of listerial febrile gastroenteritis, since standard stool culture media for detection of common enteric pathogens has low sensitivity for detection of Listeria. Therefore, listerial gastroenteritis is a presumptive diagnosis based on clinical manifestations and presumptive exposure in the setting of an outbreak.
In the setting of suspected Listeria gastroenteritis, there is no role for routine pursuit of stool cultures plated on special selective media, since such cultures have not been validated as a screening tool.
Differential diagnosis — The differential diagnosis of listeria gastroenteritis is broad; it includes a number of pathogens transmitted by food and water as well as C. difficile (table 2 and table 3). (See "Approach to the adult with acute diarrhea in resource-abundant settings" and "Clostridioides difficile infection in adults: Clinical manifestations and diagnosis".)
Invasive disease
Incubation period — For invasive listeriosis, the mean incubation period is 11 days; 90 percent of cases occur within 28 days [16].
Bloodstream infection — Most nonpregnant patients with Listeria bacteremia are either immunocompromised or adults of older age. Mortality with isolated bacteremia is high; in one series, the three-month mortality rate was 45 percent [17]. Bacteremia also occurs in neonates; early-onset infection is associated with maternal illness and premature birth whereas babies with late-onset disease are generally born at term without perinatal complications [18]. Early-onset neonatal disease is associated with high mortality [18]. Although Listeria may cause sepsis in immunocompromised children, it is relatively infrequent [19].
Clinical features and diagnosis — Patients with bacteremia typically present with fever and chills, and nearly a quarter of patients have had antecedent diarrhea [17]. Septic shock can develop but is rare [17]. There may be seeding of the brain and/or meninges, leading to meningoencephalitis or cerebritis; the risk of concurrent central nervous system (CNS) infection is relatively high in immunocompromised patients [20]. (See 'Central nervous system infection' below.)
The diagnosis of listerial bacteremia is established via blood cultures. There is no clinical way to distinguish this infection from a number of other entities that manifest as fever and constitutional symptoms. If blood cultures are negative but listeriosis is suspected, microbial cell-free deoxyribonucleic acid (DNA) sequencing may be sent to aid in pathogen identification [21].
Stool culture is not indicated in patients with systemic listeriosis [18,19].
Evaluation for complications — Patients with listerial bacteremia should be evaluated with a thorough history and physical exam to elucidate any neurologic signs or symptoms that raise the suspicion of CNS involvement. We perform magnetic resonance imaging (MRI) with contrast in patients with listerial bacteremia and CNS signs or symptoms. A lumbar puncture should also be performed in patients with listerial bacteremia exhibiting symptoms of CNS involvement regardless of MRI findings.
Central nervous system infection
Spectrum of CNS involvement — The most common central nervous system (CNS) manifestation of listerial infection is meningoencephalitis [17]; this may be generalized or with focal involvement of the brainstem (rhombencephalitis). Among 252 patients with CNS listeriosis in the MONALISA study, a nationwide prospective study in France, 212 (84 percent) had meningoencephalitis [17]. Listeria may also cause isolated meningitis. Cerebritis, which infrequently progresses to brain abscess, is less common. Patients can also manifest spinal and brain abscesses from hematogenous seeding [22]. The risk of CNS involvement in the setting of Listeria infection is highest in immunocompromised patients. (See 'Individuals at highest risk' above.)
The clinical presentation of Listeria CNS infection ranges from a mild illness with fever and mental status changes to a fulminant course with coma [3,5,23,24]. Many adults with CNS listerial infection do not have specific clinical signs of meningitis. As an example, in a review of 820 nonpregnant patients with CNS listeriosis, 42 percent presented without signs of meningeal irritation [24]. (See "Clinical features and diagnosis of acute bacterial meningitis in adults" and "Bacterial meningitis in children older than one month: Clinical features and diagnosis", section on 'Clinical features'.)
Focal neurologic signs suggestive of brain involvement or inflammation may be present. These include cranial nerve abnormalities, ataxia, tremors, hemiplegia, and deafness. Seizures can also occur; if they do, they often begin later in the course of the illness. In the review of 820 patients described above, one-third had focal neurologic findings and one-quarter had seizures [24]. In a prospective study of 30 adults with Listeria meningitis, 43 percent of patients had the triad of fever, neck stiffness, and altered mental status; only 37 percent of patients had focal neurologic deficits [25]. In a cohort study of 818 cases of listeriosis, which included 252 cases of neurolisteriosis, the majority of patients with neurolisteriosis presented with encephalitis-associated symptoms (87 percent) [17]; meningeal involvement without encephalitis was only seen in 13 percent of patients, and brainstem involvement was observed in only 17 percent. Occasionally, cerebritis can result from direct hematogenous invasion of cerebral parenchyma, usually with little or no involvement of the meninges [26]. In such cases, patients may have fever, headache, and focal neurologic signs in the absence of other meningeal signs.
Rhombencephalitis (encephalitis involving the brainstem and/or cerebellum) is a relatively uncommon manifestation of listerial meningoencephalitis that typically occurs in healthy individuals who have acquired Listeria via contaminated food consumption, often in outbreaks. Among 252 cases of CNS listeriosis in a nationwide prospective study in France, 42 (17 percent) had brainstem involvement [17]. Rhombencephalitis often follows a biphasic course, beginning with headache, fever, nausea, and vomiting, followed over the course of several days by cranial nerve palsies, ataxia, tremor, and other cerebellar signs, decreased consciousness, and possibly seizures and hemiparesis. Almost one-half develop respiratory failure.
Progression to frank brain abscess is an uncommon complication. One case series reported five patients with listerial brain abscess, three of whom were cardiac transplant recipients [22]. Focal neurologic symptoms were present in 87 percent of patients combining these five cases with a review of 34 previously published cases from 1966 to 2000.
CSF findings — Analysis of the cerebrospinal fluid (CSF) in patients with CNS Listeria infection, even in cases of rhombencephalitis, may reveal only mild abnormalities [24,27]. It may show a pleocytosis, with a differential that can range from 100 percent polymorphonuclear cells to 100 percent mononuclear cells. Listeria is the one nontuberculous bacteria that causes a substantial number of lymphocytes in the CSF in the absence of antibiotic therapy. In a review of 820 patients, the CSF protein concentration was moderately elevated in almost all patients (mean 168 mg/dL) and the CSF glucose concentration was reduced in 39 percent [24]. CSF Gram stain is usually negative, but culture is usually positive for Listeria, even when the CSF profile is only mildly abnormal or shows a lymphocytic predominance [5]. Rarely, blood cultures can be positive when the CSF culture is not [24].
Evaluation and diagnosis — As with any case of suspected bacterial meningitis, lumbar puncture with CSF analysis, culture, and PCR, if available, should be obtained in all cases of patients clinically suspected of CNS listeriosis. Blood cultures should also be obtained. A definitive diagnosis of listerial CNS infection can be made when CSF cultures or PCR are positive for Listeria. If CSF culture and PCR are negative but blood cultures are positive and the patient exhibits signs or symptoms of CNS involvement, then a diagnosis of CNS listeriosis can also be made. Gram stain of the CSF in Listeria meningitis has a low sensitivity, being positive (for gram-positive rods) in only about one-third of patients. In an immunocompromised, chronically ill, or older adult patient with a negative Gram stain and acute meningitis, an evaluation for Listeria should be pursued prior to making a presumptive diagnosis of viral (aseptic) meningitis.
Cases of Listeria of the CNS may rarely have negative CSF cultures but positive blood cultures [24]. In a review of 820 cases of listeriosis, blood cultures were positive in 71 percent of the 257 patients with meningitis/meningoencephalitis [24]. A small number of patients with CNS infection other than meningitis also may have positive blood cultures with negative CSF cultures. In a literature review that included 10 patients with Listeria brain abscess/cerebritis without meningitis, Listeria was cultured from the blood in eight but from the CSF in only two. Similarly, blood cultures were more often positive than CSF cultures (61 versus 41 percent) in a review of patients with rhombencephalitis [24,28].
Increasingly, invasive listeriosis is being diagnosed with culture-independent diagnostic technologies (such as multiplex PCR panel for meningitis/encephalitis) [12]. A real-time PCR assay for the hly gene, which encodes listeriolysin O, can be used on CSF to detect Listeria and appears to be specific and more sensitive than culture [24,25,29,30].
If initial CSF microbiology tests and blood cultures are negative but listerial CNS infection is still suspected because of a compatible clinical or radiologic picture, repeat CSF and blood cultures are warranted.
We also pursue radiographic imaging in patients with known or suspected listerial meningoencephalitis. MRI with contrast (image 1) is more sensitive than computed tomographic (CT) (image 2) for the detection of Listeria lesions in the cerebellum, brainstem, and cortex [28,31]. MRI better demonstrates the brainstem abnormalities than CT scan, which is often normal at presentation [28]. High-signal lesions on T2-weighted images and enhancing lesions on T1-weighted images after the administration of intravenous contrast are seen in the cerebral parenchyma.
Differential diagnosis — The differential diagnosis of Listeria CNS infection depends on the clinical presentation.
For those who present with classic features of meningitis and have a polymorphonuclear pleocytosis in the CSF, other causes of typical bacterial meningitis are the primary considerations (table 4). (See "Clinical features and diagnosis of acute bacterial meningitis in adults", section on 'Cerebrospinal fluid analysis'.)
However, Listeria can also present with a lymphocytic CSF pleocytosis, in which case viral, fungal, and mycobacterial etiologies are other considerations. The distinction between these is typically made on culture or other microbiologic testing and is discussed in detail elsewhere. (See "Aseptic meningitis in adults".)
For patients who present with symptoms of rhombencephalitis (focal involvement of the brainstem), Listeria is the most common infectious cause; however, noninfectious causes can also result in a similar clinical presentation. In one series of 97 patients with rhombencephalitis, most cases (n = 31) were of unknown etiology, and multiple sclerosis (n = 28) was the most common identified cause overall [32]. Unlike other etiologies, listerial rhombencephalitis was associated with a low level of consciousness in 78 percent of cases; fever and meningeal signs were more common than in other causes of rhombencephalitis. Other noninfectious conditions that can cause brainstem and/or cerebellar lesions include sarcoidosis, systemic rheumatic diseases (Behçet syndrome, systemic lupus erythematosus, relapsing polychondritis), lymphoma, and paraneoplastic syndromes and should be considered if infectious etiologies, including Listeria have been ruled out or considered unlikely.
Other infectious etiologies of encephalitis that may involve the brainstem and/or cerebellum include herpes simplex virus [33], Lyme disease, Epstein-Barr virus, and Brucella. In patients with an immunocompromising condition, additional considerations include toxoplasmosis, cryptococcosis, and reactivation of John Cunningham virus. Tuberculosis is also a possible cause of rhombencephalitis in patients with relevant epidemiologic risk. The distinction is usually made based on culture or molecular testing of CSF. In some cases, empiric treatment for some of these other etiologies is warranted pending microbiologic results.
Focal infection — Numerous focal manifestations of listeriosis have been described in case reports and small series [5,24]. Most of these focal infections have no distinctive characteristics but tend to occur more commonly in immunocompromised patients. The diagnosis is usually established by recovery of Listeria in culture from a relevant body site.
●Skin or eye infections as a result of direct inoculation are a rare occurrence in veterinarians, farmers, and laboratory workers [27].
●Cholecystitis can result from hematogenous seeding, and acute hepatitis simulating viral hepatitis can be seen in patients with disseminated infection [34]. In a review of 20 cases of biliary tract disease, there were 17 cases of cholecystitis, 2 cases of cholangitis, and 1 case of biliary tract cyst infection [35].
●Peritonitis can occur in patients treated with continuous ambulatory peritoneal dialysis and those with cirrhosis [36,37].
●Other complications include Parinaud oculoglandular syndrome, lymphadenitis [38], pneumonia and empyema [39], myocarditis [21], endocarditis (usually with a subacute presentation), septic arthritis, osteomyelitis, prosthetic joint infection [40], necrotizing fasciitis [41], arteritis, prosthetic graft infection [42], and biliary tract infection [35].
PREGNANT PATIENTS — The incidence of listeriosis associated with pregnancy is approximately 10 times higher than in the general population [15,43-45].
Clinical manifestations — Listerial syndromes in pregnancy include febrile gastroenteritis and bacteremia. They are diagnosed most commonly during the third trimester.
Maternal infection may present as a nonspecific, flu-like illness with fever, myalgia, abdominal or back pain, nausea, vomiting, or diarrhea [46]. Listeria infection may be mild and resolve without therapy, and the diagnosis missed if blood cultures are not obtained [5,14]. Among pregnant women with listeria bacteremia, CNS involvement is relatively uncommon [23].
Outcomes for pregnant women with Listeria are typically good; however, fetal and neonatal infections can be severe, leading to fetal loss, preterm labor, neonatal sepsis, meningitis, and death. (See "Treatment and prevention of Listeria monocytogenes infection", section on 'Outcomes'.)
Diagnostic approach — Listeriosis should be suspected in pregnant women with presumptive Listeria exposure (table 1) and relevant symptoms (including myalgia, abdominal or back pain, nausea, vomiting, or diarrhea), with or without fever ≥38.1°C (100.6°F) (algorithm 1) [15].
For pregnant women with presumptive Listeria exposure and relevant symptoms including fever (temperature ≥38.1°C or 100.6°F), in the absence of an alternative cause of illness, blood cultures should be obtained and empiric parenteral antibiotic treatment should be initiated [15]. Antenatal maternal treatment is associated with less severe listeriosis in the neonate [47]. In addition, stool studies (including stool culture for detection of common enteric pathogens [or multiplex PCR in centers where available] and testing for C. difficile) should be obtained to evaluate for alternative causes of diarrheal illness. Stool cultures for Listeria are not indicated as they are not validated as a diagnostic tool. (See "Treatment and prevention of Listeria monocytogenes infection", section on 'Febrile illness'.)
For pregnant women with presumptive Listeria exposure and relevant symptoms but temperature <38.1°C (100.6°F), in the absence of an alternative cause of illness, the optimal approach is uncertain. We obtain blood cultures and stool studies (including stool culture for detection of common enteric pathogens [or multiplex PCR in centers where available] and testing for C. difficile), and initiate empiric oral antibiotic therapy, although it is unclear whether this will improve fetal outcomes [48,49]. Subsequent management and fetal evaluation should be guided by the patient’s clinical status and culture results. (See "Treatment and prevention of Listeria monocytogenes infection", section on 'Mild illness'.)
For pregnant women with presumptive Listeria exposure who are asymptomatic, no diagnostic evaluation is necessary and no empiric antibiotic treatment is warranted; such patients should be advised to return for evaluation if symptoms develop within two months of presumptive exposure [15]. (See "Treatment and prevention of Listeria monocytogenes infection", section on 'No symptoms'.)
FETAL AND NEONATAL INFECTION — Fetal and neonatal infections can be severe, leading to fetal loss, preterm labor, neonatal sepsis, meningitis, and death [14,17,46,50-54].
Transplacental transmission may result in granulomatosis infantiseptica. Infants with this disorder have disseminated abscesses and/or granulomas in multiple internal organs (liver, spleen, lungs, kidneys, brain). Skin lesions, papular or ulcerative, may be present. Most neonates with granulomatosis infantiseptica are stillborn or die soon after birth [5]. Placental histopathology is distinctive since there is both a pronounced chorioamnionitis and an acute villitis with abscess formation (picture 4) [55]. The organisms are often visible within the amnion epithelium without special stains but are clearly demonstrated with Gram stain or methenamine silver stain.
Neonates probably acquire infection during or after birth. Infection in the first week of life is usually manifested by sepsis, while disease manifestations after the first week are more variable and often include meningitis. Early-onset sepsis is characterized by high neonatal mortality in association with maternal illness and premature delivery. With late-onset disease, babies generally are full term and have no history of perinatal complications [18]. Listeria meningoencephalitis most often occurs in neonates after three days of age. Manifestations of infection and outcomes are related to the gestational age at birth and the timing in pregnancy when maternal disease occurs. In a prospective study of 189 neonates born to mothers with listeriosis at the time of delivery, 15 of the 17 neonates that had major adverse events (eg, death, severe brain injury, or bronchopulmonary dysplasia) were born ≤34 weeks of gestation [47]. Timing of maternal disease in pregnancy is discussed elsewhere. (See 'Pregnant patients' above.)
The evaluation of neonatal sepsis and meningitis are discussed in detail elsewhere. Briefly, this includes cultures of blood and CSF; Listeria grows well on common media. If feasible, culture of placenta should also be obtained. (See "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates" and "Bacterial meningitis in the neonate: Clinical features and diagnosis".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bacterial meningitis in adults" and "Society guideline links: Infectious encephalitis" and "Society guideline links: Bacterial meningitis in infants and children".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Basics topic (see "Patient education: Listeria infection (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Individuals at highest risk − Listeria monocytogenes primarily causes invasive disease, including central nervous system (CNS) infection or bacteremia in immunosuppressed patients, individuals at the extremes of age, and pregnant women. Listeria is also a cause of self-limited febrile gastroenteritis in normal hosts. (See 'Individuals at highest risk' above.)
●Non-pregnant patients − In nonpregnant patients, manifestations of listeriosis include gastroenteritis, bloodstream infection, and CNS infection. (See 'Nonpregnant patients' above.)
•Gastroenteritis − Gastroenteritis due to L. monocytogenes is a presumptive diagnosis based on clinical manifestations and presumptive exposure in the setting of an outbreak. It is difficult to establish a definitive diagnosis in the absence of bacteremia since standard stool culture media has low sensitivity for detection of Listeria. Stool culture (or multiplex polymerase chain reaction [PCR] in centers where available) should be obtained to evaluate for common alternative causes of diarrheal illness, and blood culture should be obtained for patients who are febrile and/or immunocompromised. (See 'Gastroenteritis' above.)
•Bloodstream infection − Bacteremia due to L. monocytogenes typically manifests with fever and chills, and nearly a quarter of patients have had antecedent diarrhea. Bacteremia primarily occurs in patients who are immunocompromised or of older age. The diagnosis is established by blood cultures. (See 'Bloodstream infection' above.)
•Central nervous system infection − CNS involvement of L. monocytogenes most commonly manifests with meningoencephalitis, which ranges from a mild illness with fever and mental status changes to a fulminant course with coma. Many patients do not have signs of meningeal irritation. Patients suspected CNS listeriosis should undergo lumbar puncture with cerebrospinal fluid (CSF) analysis, culture, and PCR, if available, as well as magnetic resonance imaging with contrast (image 1). Diagnosis can be made by detection of L. monocytogenes on CSF culture or PCR or if blood cultures are positive in a patient with symptoms and signs of CNS involvement. (See 'Central nervous system infection' above.)
●Pregnant patients − In pregnant patients, manifestations of listeriosis include gastroenteritis and bacteremia; pregnant patients are diagnosed most commonly during the third trimester. Listeriosis should be suspected in pregnant patients with presumptive Listeria exposure (table 1) and relevant symptoms (including myalgia, abdominal or back pain, nausea, vomiting, or diarrhea), with or without fever ≥38.1°C (100.6°F) (algorithm 1). (See 'Clinical manifestations' above.)
•For pregnant patients with presumptive Listeria exposure and relevant symptoms including fever (temperature ≥38.1°C or 100.6°F), in the absence of an alternative cause of illness, we obtain blood cultures and administer empiric parenteral antibiotic treatment. In addition, stool studies should be obtained to evaluate for alternative causes of diarrheal illness. (See 'Diagnostic approach' above and "Treatment and prevention of Listeria monocytogenes infection", section on 'Febrile illness'.)
•For pregnant patients with presumptive Listeria exposure and relevant symptoms but temperature <38.1°C (100.6°F), in the absence of an alternative cause of illness, the optimal approach is uncertain. We obtain blood cultures and stool studies and administer empiric oral antibiotic therapy. Subsequent management and fetal evaluation should be guided by the patient’s clinical status and culture results. (See 'Diagnostic approach' above and "Treatment and prevention of Listeria monocytogenes infection", section on 'Mild illness'.)
•For pregnant women with presumptive Listeria exposure who are asymptomatic, no diagnostic evaluation is necessary and no empiric antibiotic treatment is warranted; such patients should be advised to return for evaluation if symptoms develop within two months of presumptive exposure. (See 'Diagnostic approach' above and "Treatment and prevention of Listeria monocytogenes infection", section on 'No symptoms'.)
●Fetal and neonatal infection − Fetal and neonatal infections can be severe. Infection acquired in utero often leads to intrauterine fetal demise. Neonates probably acquire infection during or after birth. Disease in the first week of life usually manifests as sepsis, while disease manifestations after the first week are more variable and often include meningitis. Early-onset sepsis is characterized by high mortality; most affected neonates are premature. With late-onset disease, babies generally are full term and have no history of perinatal complications. (See 'Fetal and neonatal infection' above.)
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