Residency · Residency · Neurology

Bacterial Meningitis: Emergency Recognition and Treatment

Introduction

Bacterial meningitis remains a neurological emergency with mortality rates of 15-25% even with appropriate treatment. Rapid recognition, immediate empiric antibiotic therapy, and supportive care are critical to reducing mortality and long-term neurological sequelae. Every minute of delay in antibiotic administration worsens outcomes.

Epidemiology and Microbiology

Common Pathogens by Age Group

In neonates (0-1 month), the predominant organisms are Group B Streptococcus (Streptococcus agalactiae), Escherichia coli (especially K1 strain), and Listeria monocytogenes. In infants and children (1 month to 18 years), Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae type b (now rare with vaccination) are the principal pathogens. In adults aged 18-50 years, Streptococcus pneumoniae is most common, followed by Neisseria meningitidis. In older adults greater than 50 years and immunocompromised patients, Streptococcus pneumoniae, Listeria monocytogenes, and aerobic gram-negative bacilli predominate. In post-neurosurgical and CSF shunt patients, Staphylococcus aureus, coagulase-negative staphylococci, and gram-negative bacilli such as Pseudomonas and Klebsiella are typical.

Clinical Presentation

Classic Triad

The classic triad of fever, neck stiffness, and altered mental status is present together in only 40-45% of cases. However, at least two of four features (headache, fever, neck stiffness, altered mental status) are present in more than 95% of cases.

Signs and Symptoms

Patients present with severe headache, photophobia, nausea, and vomiting. The Kernig sign (resistance to passive knee extension with hip flexed at 90 degrees) and Brudzinski sign (involuntary hip and knee flexion with passive neck flexion) are classic but have limited sensitivity of approximately 5% each; their absence does not rule out meningitis. The jolt accentuation test, in which headache worsens with horizontal rotation of the head at 2-3 Hz, is more sensitive than classic meningeal signs. A petechial or purpuric rash is strongly suggestive of meningococcal meningitis and can progress to purpura fulminans with disseminated intravascular coagulation.

Complications

Complications include seizures (occurring in 20-30% of patients), cerebral edema and elevated ICP, cerebral venous sinus thrombosis, subdural empyema or brain abscess, hydrocephalus, cranial nerve palsies (especially CN VIII causing hearing loss), and cerebral infarction from vasculitis or vasospasm.

Diagnostic Approach

When to Obtain CT Before Lumbar Puncture

CT head should be obtained before LP only in patients with an immunocompromised state, history of CNS disease (mass lesion, stroke, focal infection), new-onset seizure within one week, papilledema, altered level of consciousness, or focal neurological deficit. Critically, antibiotics must not be delayed while awaiting CT. Blood cultures should be drawn and empiric antibiotics administered immediately, with imaging and LP to follow.

CSF Analysis

Opening pressure is elevated, typically greater than 20 cm H2O and often greater than 30. The WBC count is usually 1,000-5,000 cells/mcL with neutrophilic predominance (greater than 80% PMNs). Protein is elevated, often greater than 100-200 mg/dL. Glucose is low, less than 40 mg/dL or with a CSF-to-serum glucose ratio less than 0.4. Gram stain is positive in 60-90% of untreated bacterial meningitis. CSF culture is the gold standard, positive in 70-85% of untreated cases. CSF lactate greater than 35 mg/dL (greater than 3.9 mmol/L) supports a bacterial etiology. Multiplex PCR panels such as BioFire FilmArray provide rapid identification of common pathogens within 1 hour.

Blood Studies

Blood cultures are positive in 50-75% of cases and must be obtained before antibiotics. A complete blood count, comprehensive metabolic panel, and coagulation studies should be sent. Procalcitonin and C-reactive protein are elevated in bacterial meningitis and may help distinguish it from viral causes.

Treatment

Empiric Antibiotic Therapy (Administer Immediately)

For adults aged 18-50 years, the regimen is ceftriaxone 2 g IV every 12 hours plus vancomycin 15-20 mg/kg IV every 8-12 hours. For those over 50, immunocompromised, or with alcoholism, ampicillin 2 g IV every 4 hours is added for Listeria coverage. For neonates, the combination is ampicillin plus gentamicin or cefotaxime. For post-neurosurgical or CSF shunt infections, vancomycin plus cefepime or meropenem provides Pseudomonas coverage.

Adjunctive Dexamethasone

Dexamethasone 0.15 mg/kg IV every 6 hours for 4 days should be initiated 15-20 minutes before or with the first dose of antibiotics. It has proven mortality benefit in pneumococcal meningitis in high-income countries, as demonstrated in the European Dexamethasone Study. The mechanism involves reduction of subarachnoid space inflammation, blood-brain barrier disruption, and cerebral edema. The benefit is less clear in meningococcal or other bacterial meningitis, though empiric administration is still recommended pending pathogen identification.

Directed Therapy (After Culture and Sensitivity)

For penicillin-sensitive S. pneumoniae, penicillin G or ceftriaxone is used for 10-14 days. For penicillin-resistant S. pneumoniae, ceftriaxone plus vancomycin is given for 10-14 days. N. meningitidis is treated with penicillin G or ceftriaxone for 7 days. L. monocytogenes requires ampicillin plus gentamicin for synergy, for 21 days or more. H. influenzae is treated with ceftriaxone for 7 days. Gram-negative bacilli require ceftriaxone or meropenem based on susceptibility for 21 days.

Supportive Care

ICU admission for close neurological monitoring is standard. Seizures are managed with levetiracetam or other antiseizure medications. ICP management if elevated includes head of bed elevation and osmotic therapy. Fluid management focuses on avoiding hyponatremia and monitoring for SIADH.

Prevention

Meningococcal vaccination with MenACWY and MenB vaccines is recommended for adolescents, college students, asplenic patients, and complement-deficient individuals. Pneumococcal vaccination with PCV15 or PCV20 is indicated for children and high-risk adults. Chemoprophylaxis for close contacts of meningococcal meningitis with rifampin, ciprofloxacin, or ceftriaxone should be administered within 24 hours of case identification.

Clinical Pearls

Antibiotics should never be delayed for imaging or LP; if there is clinical suspicion for bacterial meningitis, blood cultures should be drawn and empiric antibiotics started immediately. The classic triad of fever, neck stiffness, and altered mental status is present in fewer than half of patients, so a low threshold for LP should be maintained in febrile patients with headache. Dexamethasone must be given before or with the first antibiotic dose to be effective and has no proven benefit if started after antibiotics. Ampicillin for Listeria coverage should be added in all patients over 50 years old, immunocompromised patients, and pregnant women. Hearing loss is the most common long-term sequela of bacterial meningitis, and audiometric testing should be performed in all survivors.

References

1. van de Beek D, Cabellos C, Dzupova O, et al. ESCMID guideline: diagnosis and treatment of acute bacterial meningitis. Clin Microbiol Infect. 2016;22(Suppl 3):S37-S62.
2. Tunkel AR, Hartman BJ, Kaplan SL, et al. Practice guidelines for the management of bacterial meningitis. Clin Infect Dis. 2004;39(9):1267-1284.
3. de Gans J, van de Beek D. Dexamethasone in adults with bacterial meningitis. N Engl J Med. 2002;347(20):1549-1556.
4. McGill F, Heyderman RS, Panagiotou S, Tunkel AR, Solomon T. Acute bacterial meningitis in adults. Lancet. 2016;388(10063):3036-3047.

For the intern

At 3am, if you suspect bacterial meningitis, act immediately: draw blood cultures, start empiric antibiotics (ceftriaxone + vancomycin, add ampicillin if >50 years old), and give dexamethasone 0.15 mg/kg before or with the first antibiotic dose. Do not delay antibiotics for imaging or lumbar puncture (LP). Only get a head CT before LP if the patient has immunocompromise, CNS disease history, new seizure, papilledema, altered consciousness, or focal deficits. If any of these are present, still give antibiotics first, then CT, then LP. The LP and full workup can wait until after you've started treatment—every minute counts. Admit to ICU. In the morning, follow up CSF studies, adjust antibiotics based on culture results, and arrange audiology testing before discharge since hearing loss is the most common long-term complication.

Common pitfalls

• Waiting for imaging or LP before antibiotics: The mortality benefit of early antibiotics outweighs diagnostic yield. Start treatment on clinical suspicion alone.
• Forgetting ampicillin for Listeria: All patients over 50, immunocompromised, or pregnant need ampicillin added to the regimen. Ceftriaxone doesn't cover Listeria.
• Giving dexamethasone late: Steroids only help if given before or with the first antibiotic dose—they reduce inflammation during bacterial lysis.
• Ruling out meningitis because meningeal signs are absent: Kernig and Brudzinski signs have only 5% sensitivity. Use clinical gestalt: headache, fever, and altered mental status in any combination warrant LP.

<image> A decision flowchart with three main panels:

Panel 1 (Top): "Patient with fever + headache ± altered mental status" leads to immediate decision diamond: "High-risk features for herniation? (immunocompromise, CNS disease, seizure, papilledema, altered LOC, focal deficit)". Arrow labeled "NO" leads to "Draw blood cultures → Start antibiotics + dexamethasone → Lumbar puncture". Arrow labeled "YES" leads to "Draw blood cultures → Start antibiotics + dexamethasone → Head CT → then LP if safe".

Panel 2 (Middle): Box labeled "Empiric antibiotic selection by age" with three branches: "Age 18-50: Ceftriaxone + Vancomycin"; "Age >50 or immunocompromised: Add Ampicillin"; "Post-neurosurgery/shunt: Vancomycin + Cefepime".

Panel 3 (Bottom): "CSF results" showing four boxes: "WBC >1000, PMN predominant, Protein >100, Glucose <40 or ratio <0.4" → "Bacterial meningitis confirmed" → "Continue treatment, ICU monitoring, adjust based on culture/sensitivities" </image>

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