Infectious Disease · PANCE / PANRE

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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