- Citrobacter species are Gram-negative, facultatively anaerobic bacilli from the Enterobacteriaceae family.
- They are rare but serious pathogens in neonates, predominantly affecting the central nervous system (CNS).
- Citrobacter koseri (formerly Citrobacter diversus) is responsible for over 90% of Citrobacter meningitis cases in neonates.
- Citrobacter freundii contributes to about 6.4% of cases.
- Unlike other Gram-negative meningitides, Citrobacter is associated with brain abscess formation in approximately 75% of affected neonates.
- Infection usually begins with bacteremia and progresses to leptomeningitis, ventriculitis, and abscess formation.
- Citrobacter can disrupt the ependymal lining and directly invade adjacent brain tissue.
- C. freundii can invade and replicate in human brain microvascular endothelial cells.
- Outer membrane proteins may contribute to the organism’s neurovirulence.
- Vertical transmission from the mother is suspected in early-onset disease and supported by evidence of maternal infection.
- Horizontal (nosocomial) transmission is more common in late-onset disease and often linked to NICU outbreaks.
- Outbreaks have been traced to contaminated infant formula and colonized hospital staff.
- Case reports describe infections in dizygotic twins, highlighting risk to asymptomatic co-twins.
- High risk of abscess mandates neuroimaging in all proven Citrobacter meningitis cases.
- Bedside cranial ultrasound is useful for unstable neonates.
- MRI is the preferred modality; CT can be used when MRI is unavailable.
- Serial imaging helps monitor disease progression and response to treatment.
- Empiric antibiotics include:
- Third-generation cephalosporins
- Imipenem
- Chloramphenicol
- Trimethoprim–sulfamethoxazole
- Gentamicin
- Combination of ciprofloxacin and meropenem is suggested for brain abscess due to better CNS penetration and sensitivity profile.
- Fluoroquinolones should be avoided in neonates due to risk of arthropathy in weight-bearing joints.
- Duration of treatment:
- Minimum of 21 days for meningitis (or 14 days after negative cultures).
- 4–6 weeks of antibiotics for brain abscess.
- Neurosurgical consultation is essential for aspiration or drainage of abscesses.
- Goals of surgery:
- Relieve mass effect
- Reduce bacterial load
- Improve antibiotic efficacy
- Aspiration may be difficult in cases with multiple or inaccessible abscesses.
- Some cases may be successfully treated with antibiotics alone.
- Intrathecal or intra-abscess antibiotics have not been proven to improve outcomes.
- Mortality rate is approximately 30% despite therapy.
- Nearly two-thirds of survivors have long-term neurological impairments.
- Citrobacter meningitis is rare but devastating in neonates due to its strong association with brain abscess formation.
- Early diagnosis, serial imaging, prompt antibiotic therapy, and surgical intervention are key to improving outcomes.
- All survivors should undergo long-term neurodevelopmental follow-up.
