Workup and Empiric Antibiotic Management for Suspected Bacterial Meningitis in Adults
Immediate Action: Antibiotics First
Initiate empiric antibiotics immediately upon suspicion of bacterial meningitis—within one hour of presentation—regardless of whether imaging or lumbar puncture has been performed, because early treatment is the single most important factor influencing mortality and morbidity. 1, 2
Clinical Recognition: What to Look For
Core Symptom Complex
- At least 95% of patients have two or more of these four symptoms: headache, fever, neck stiffness, or altered mental status. 1
- The classic triad (fever, neck stiffness, altered mental status) appears in fewer than 50% of cases, so its absence cannot exclude meningitis. 1, 3
Individual Symptom Frequencies in Adults
- Headache: 58–87% 1, 3
- Fever: 77–97% 1, 3
- Neck stiffness: 65–83% 1, 3
- Altered mental status: 30–69% 1, 3
Critical Rash Finding
- A petechial or purpuric rash indicates meningococcal disease in >90% of cases when present with meningitis symptoms. 1, 3
- Rash occurs in 20–52% of adult meningitis patients overall 1, 3
Additional Features
- Seizures occur in 10–25% of adults 1
- Focal neurologic deficits appear in 11–34% of bacterial cases 1
- Photophobia is common (55% in one series) 4
Physical Exam Limitations—A Critical Pitfall
- Kernig and Brudzinski signs have only 5–11% sensitivity in adults and cannot rule out meningitis. 1, 3
- Neck stiffness itself has only 31% sensitivity, missing 69% of actual cases. 1, 3
Age-Specific Considerations
Elderly Patients (>65 years)
- More likely to present with altered consciousness but less likely to have fever or neck stiffness. 1
- Listeria monocytogenes and Streptococcus pneumoniae are the most likely pathogens in this age group. 1
Immunocompromised, Alcoholic, or Diabetic Patients
- These populations have blunted presentations and require especially low threshold for workup 5, 6
- Listeria is the second most common pathogen after S. pneumoniae in immunocompromised patients 1
Diagnostic Workup Algorithm
Step 1: Blood Cultures and Immediate Antibiotics
- Obtain blood cultures, then start empiric antibiotics immediately—do not wait for imaging or lumbar puncture. 1, 7
Step 2: Determine Need for CT Before LP
Perform CT head before lumbar puncture only if the patient has:
- New focal neurologic deficit
- Moderate-to-severe altered mental status
- Immunocompromised state
- History of CNS disease (mass lesion, stroke, infection)
- New-onset seizure 7
If none of these features are present, proceed directly to lumbar puncture without imaging. 7
Step 3: Lumbar Puncture
- CSF examination is the principal diagnostic test with the highest accuracy (AUC 0.95) for bacterial meningitis. 1
- Target LP and antibiotic administration within one hour of hospital arrival. 1
- Key CSF findings in bacterial meningitis: elevated white blood cell count (predominantly neutrophils), elevated protein, and low glucose 3, 4
Empiric Antibiotic Regimen
Standard Adult Regimen (Age <50, Immunocompetent)
Ceftriaxone 2g IV every 12 hours 1
Add Vancomycin If:
- Suspected pneumococcal meningitis with potential ceftriaxone resistance
- Septic cavernous sinus thrombosis suspected (S. aureus including CA-MRSA) 1
- Regional resistance patterns warrant broader coverage 7
Note: North American guidelines recommend vancomycin for all patients, while Australian/UK/European guidelines reserve it for higher-risk scenarios. 7
Add Ampicillin 2g IV Every 4 Hours If:
This addition covers Listeria monocytogenes, which is critical in these populations. 1, 7
Adjunctive Dexamethasone
Administer dexamethasone as routine empirical therapy because it reduces morbidity and mortality from pneumococcal meningitis. 7
Common Pitfalls to Avoid
Pitfall 1: Waiting for Imaging
Never delay antibiotics for CT imaging—harmful delays from waiting for neuroimaging worsen outcomes. 7
Pitfall 2: Relying on Classic Signs
Do not rule out meningitis based on absent neck stiffness or negative Kernig/Brudzinski signs—these have abysmal sensitivity. 1, 3
Pitfall 3: Missing Listeria Coverage
Always add ampicillin for patients >50 years or with risk factors—Listeria is not covered by ceftriaxone alone. 1, 7
Pitfall 4: Subtle Presentations in Elderly
Maintain high suspicion in elderly patients who may present only with confusion and minimal fever. 1, 6
Pitfall 5: Antibiotic Pretreatment Masking Diagnosis
Patients already on antibiotics may have misleading presentations, making CSF analysis even more critical 6
Special Consideration: Tuberculosis Meningitis
If subacute onset (days to weeks) with:
- Cranial nerve palsies (especially sixth nerve) 8
- Lymphocytic CSF pleocytosis with low glucose 8
- Risk factors for TB exposure
Start antitubercular therapy promptly based on clinical suspicion, as delayed treatment significantly increases mortality and neurological morbidity. 8