Listeriosis
Gram-positive rod causing febrile gastroenteritis in healthy hosts and invasive disease — meningoencephalitis, bacteremia, and stillbirth — in pregnancy, neonates, elderly, and immunocompromised.
Also known as: Listeria monocytogenes, Listeria meningitis, neonatal listeriosis, granulomatosis infantiseptica
Overview
Infection with Listeria monocytogenes, a facultative intracellular, gram-positive, catalase-positive, beta-hemolytic, tumbling-motile rod that crosses the placental, intestinal, and blood-brain barriers. Causes a benign febrile gastroenteritis in healthy adults but invasive disease in vulnerable hosts.
Epidemiology
Approximately 1,600 invasive cases per year in the US (CDC), with case-fatality near 20%. Outbreaks linked to deli meats, soft cheeses, raw milk, melons, and refrigerated ready-to-eat foods. Listeria uniquely grows at refrigeration temperatures.
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Risk factors
- Pregnancy (~17-fold increased risk; second/third trimester)
- Neonates (early-onset and late-onset)
- Age >65
- Immunocompromise: solid organ transplant, hematologic malignancy, high-dose steroids, TNF inhibitors, HIV
- Iron overload, hemochromatosis
- Consumption of unpasteurized dairy, deli meats, soft cheeses, raw sprouts
Pathophysiology
Ingested bacteria cross the gut epithelium via internalin-E-cadherin interaction. Inside macrophages, listeriolysin O lyses the phagosome, allowing intracellular replication and actin-based ('comet tail') cell-to-cell spread. Tropism for the placenta and CNS drives the most feared complications. Cell-mediated immunity (Th1/IFN-γ) is required for clearance, explaining susceptibility in steroid and TNF-inhibitor users.
Clinical presentation
Symptoms
- Healthy adults: self-limited febrile gastroenteritis 24 h after exposure
- Pregnant: flu-like illness — fever, myalgias, back pain — frequently without GI symptoms
- Invasive (elderly/immunocompromised): meningitis or meningoencephalitis with headache, fever, confusion, seizures, focal deficits
- Neonatal early-onset (<7 days): sepsis, pneumonia, granulomatosis infantiseptica (disseminated microabscesses)
- Neonatal late-onset (1-4 weeks): meningitis
Signs / physical exam
- Meningismus less reliable in elderly and immunocompromised
- Brainstem signs and rhombencephalitis — cranial nerve palsies, ataxia, altered mental status (a distinctive Listeria pattern)
- Maternal fever near term; fetal distress on monitoring
- Neonatal respiratory distress, hepatosplenomegaly, skin/throat granulomas
Classic findings
Rhombencephalitis (brainstem involvement) in a healthy or mildly immunocompromised adult is highly suggestive.
Differential diagnosis
- Bacterial meningitis (pneumococcus, meningococcus, GBS, H. influenzae) — Younger and middle-aged adults; Listeria preferred over these in age >50, pregnancy, and immunocompromise
- Viral meningoencephalitis (HSV, enterovirus) — Lymphocytic CSF predominance, normal glucose; HSV PCR and clinical course separate
- TB meningitis — Subacute course, low CSF glucose, basal meningeal enhancement on MRI
- Neonatal GBS sepsis — Early-onset GBS dominates in the first week; late-onset Listeria can mimic late-onset GBS
- Chorioamnionitis from other causes — Maternal fever and uterine tenderness near term; consider Listeria if also flu-like illness or deli meat exposure
Diagnostic workup
Diagnostic criteria
Compatible clinical syndrome plus isolation of L. monocytogenes from a normally sterile site (blood, CSF, placenta, amniotic fluid).
Labs
- Blood cultures — high yield in invasive disease
- CSF: typically neutrophilic but may be mononuclear; mildly elevated protein, low-normal glucose
- CSF Gram stain often negative (low organism burden); listeriolysin PCR or culture confirms
- Stool culture not routinely diagnostic; selective media required
- CBC, CMP, blood gas as clinically indicated
Imaging
- MRI brain with contrast: rhombencephalitis with brainstem T2 hyperintensities, ring-enhancing abscesses; sensitive for posterior fossa involvement
- Obstetric ultrasound and fetal monitoring in pregnancy
Treatment
First-line
- Ampicillin-based therapy for listeriosis — IV ampicillin 2 g every 4 hours is the cornerstone
- Add gentamicin for synergy in severe disease (meningitis, endocarditis, neonatal sepsis)
- Trimethoprim-sulfamethoxazole IV for penicillin-allergic patients
- Duration: 14-21 days for bacteremia; 21 days or longer for meningitis; 4-6 weeks for endocarditis or brain abscess
Pregnancy
- IV ampicillin to reduce fetal transmission
- Add gentamicin in severe maternal illness (use cautiously near delivery)
- Avoid TMP-SMX in third trimester (kernicterus risk)
Neonatal listeriosis
- Ampicillin + gentamicin
- Treat 14 days for bacteremia, 21 days for meningitis
Immunocompromised meningoencephalitis
- Add ampicillin to standard empiric meningitis regimen (vancomycin + ceftriaxone) when age >50, pregnant, or immunocompromised
- Dexamethasone benefit unproven in Listeria — most guidelines do not recommend continuation if Listeria confirmed
Second-line / adjunct
- Cephalosporins are INACTIVE against Listeria — empiric meningitis regimens must include ampicillin in at-risk groups
- Linezolid or meropenem occasionally used in penicillin allergy with sulfa intolerance
Complications
- Pregnancy loss, preterm labor, stillbirth, neonatal sepsis
- Granulomatosis infantiseptica
- Meningoencephalitis, brain abscess, rhombencephalitis
- Endocarditis (rare)
- Long-term neurologic sequelae in survivors
PANCE pearls
- Add ampicillin to vancomycin + ceftriaxone for empiric meningitis in patients >50, pregnant, or immunocompromised.
- Listeria grows at refrigerator temperatures — outbreak hallmark.
- Pregnant patient with flu-like illness + deli meat exposure → think Listeria, draw blood cultures, treat empirically with IV ampicillin.
- Cephalosporins are NOT active against Listeria.
- Brainstem signs (cranial neuropathies, ataxia) in a febrile adult = rhombencephalitis pattern.
References
- IDSA 2004 — IDSA Practice Guidelines for the Management of Bacterial Meningitis (Tunkel et al., Clin Infect Dis 2004)
- CDC — CDC Listeriosis Surveillance and Outbreak Investigations
- AAP Red Book — American Academy of Pediatrics Red Book — Listeria monocytogenes
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