Can you write a concise article on meningitis covering its definition, typical presentation, diagnostic workup, empiric treatment for adults and neonates, pathogen‑specific therapy, viral management, preventive vaccinations, contact prophylaxis, and include a brief treatment algorithm?

Meningitis: Clinical Overview and Management

Definition and Epidemiology

Meningitis is inflammation of the meninges and subarachnoid space, representing a medical emergency when bacterial in origin, with mortality remaining high despite modern antibiotics and vaccination programs. 1

• Bacterial meningitis carries high case fatality rates and requires recognition within the first hour of presentation 1, 2
• The average UK district general hospital sees ten or fewer laboratory-confirmed cases annually 1
• Aseptic (predominantly viral) meningitis is more common, with an annual incidence of 7.6 per 100,000 adults 3
• Vaccination programs have dramatically altered epidemiology: pneumococcal conjugate vaccines and meningococcal C vaccines have reduced incidence of vaccine-serotype disease, though serotype replacement remains a concern 1

Clinical Presentation

Adults

The classic triad of fever, neck stiffness, and altered mental status occurs in only 44–51% of bacterial meningitis cases, meaning its absence cannot exclude the diagnosis. 4, 5

• Up to 95% of patients have at least two of four cardinal symptoms: fever, nuchal rigidity, altered mental status, and headache 5
• Kernig and Brudzinski signs have poor sensitivity (9–11%) and should not guide clinical decision-making 4, 3
• Photophobia, severe headache, vomiting, and chills are common but nonspecific 1
• Critical pitfall: Never rely on clinical examination alone to exclude bacterial meningitis—absence of classic signs should never delay treatment 4, 2

Neonates

• Neonates present with nonspecific symptoms: irritability, poor feeding, respiratory distress, pale or mottled skin, and abnormal tone 1
• Fever is present in only 6–39% of neonatal cases 1
• Seizures occur in 9–34% of cases, more commonly with group B streptococcal than E. coli meningitis 1
• Concomitant septic shock may be present in approximately 25% of neonatal meningitis cases 1
• A low threshold for lumbar puncture is essential in neonates, as clinical examination cannot rule out meningitis 1

Children Beyond Neonatal Age

• Classical signs are less frequent in younger infants compared to older children 1
• Typical presentation includes fever, chills, vomiting, photophobia, and severe headache 1
• The younger the child, the more subtle and atypical the symptoms 1

Diagnostic Workup

Immediate Actions (Within First Hour)

Obtain blood cultures immediately, perform lumbar puncture without delay unless contraindications exist, and initiate empiric antibiotics within one hour of presentation—do not wait for imaging or culture results. 1, 4, 6, 2

Indications for CT Imaging Before Lumbar Puncture

Perform urgent head CT only if any of the following are present 1, 4, 6:

• Glasgow Coma Scale ≤10–12
• Focal neurological deficits
• Recent-onset seizure
• Severe immunocompromise
• Papilledema or signs of raised intracranial pressure
• Purpuric rash suggesting meningococcal sepsis
• Cardiovascular shock requiring resuscitation
• Coagulopathy or thrombocytopenia

If CT would delay treatment, start empiric antibiotics immediately and defer imaging 4, 6

Cerebrospinal Fluid Analysis

High-Certainty Predictors of Bacterial Meningitis (≥99% certainty)

Any single one of the following CSF parameters predicts bacterial meningitis with approximately 99% certainty: 4

• CSF glucose <34 mg/dL (1.9 mmol/L)
• CSF-to-plasma glucose ratio <0.23
• CSF protein >120 mg/dL (1.2 g/L)
• CSF leukocyte count >12,000 cells/mm³
• CSF neutrophil count >11,000 cells/mm³

Parameters That Exclude Bacterial Meningitis

• CSF glucose >2.6 mmol/L makes bacterial meningitis unlikely 4
• CSF-to-plasma glucose ratio >0.36 provides 93% sensitivity and specificity for ruling out bacterial meningitis 4
• CSF protein <0.6 g/L argues against bacterial etiology 4

Additional CSF Studies

• CSF lactate ≥35 mg/dL (3.5 mmol/L) distinguishes bacterial from viral meningitis with 93% sensitivity and 96% specificity when obtained before antibiotics 4
• After antibiotic administration, CSF lactate sensitivity drops to <50% 4, 7
• Gram stain sensitivity ranges from 50–99% depending on pathogen and prior antibiotic exposure 4, 7
• CSF culture sensitivity is 70–85% without prior antibiotics 4, 7
• CSF PCR demonstrates 87–100% sensitivity and 98–100% specificity, remaining positive even after antibiotic administration 4, 7
• Broad-range 16S rRNA PCR achieves 100% sensitivity and 98.2% specificity 4

Typical CSF Profiles

Bacterial meningitis: 1, 4

• Turbid or purulent appearance
• Elevated opening pressure
• Neutrophil predominance (80–95% of cases)
• Low glucose (<40 mg/dL in 50–60%)
• Elevated protein

Viral meningitis: 1, 4

• Clear appearance
• Normal or mildly elevated opening pressure
• Lymphocyte predominance
• CSF leukocyte count 5–1,000 cells/µL (rarely >2,000)
• Normal or mildly elevated protein
• Normal glucose

Critical pitfall: Approximately 10% of bacterial meningitis cases may show lymphocytic predominance, especially after partial antibiotic treatment—never assume viral etiology based solely on cell differential 7

Serum Biomarkers

Serum CRP >20 mg/L distinguishes bacterial from viral meningitis with 96% sensitivity, 93% specificity, and 99% negative predictive value. 4

• CRP rises within approximately 6 hours of bacterial inflammation 4
• A normal CRP (<20 mg/L) has high negative predictive value and may support withholding antibiotics in select cases with negative Gram stain 4
• Procalcitonin levels between 1–2 ng/mL also show good diagnostic accuracy 4, 8
• Order CRP and procalcitonin immediately upon suspicion, preferably before antibiotics 4

Blood Cultures

Obtain two blood culture sets before antibiotic administration; expected positivity rates are approximately 75% for S. pneumoniae, 50–90% for H. influenzae, and 40–60% for N. meningitidis. 4

• Blood cultures are positive in only 40–75% of confirmed bacterial meningitis cases 4
• Prior antibiotic therapy reduces blood culture yield by approximately 20% 4, 7
• Blood cultures remain valuable when CSF is unavailable or culture-negative 4

Effect of Prior Antibiotics on Diagnostic Yield

• CSF sterilization occurs within 2 hours for N. meningitidis and 4 hours for S. pneumoniae after antibiotic administration 4, 7
• CSF biochemical parameters (glucose, protein, cell counts) remain interpretable for up to 48 hours after starting parenteral antibiotics 4, 7
• Gram stain sensitivity decreases by approximately 20% after antibiotic exposure 7
• CSF culture sensitivity drops by 10–20% with prior antibiotics 7
• CSF PCR remains highly sensitive even after antibiotic administration 7

Empiric Antimicrobial Treatment

Adults (Immunocompetent)

For adults with suspected bacterial meningitis, initiate vancomycin plus ceftriaxone (or cefotaxime) within one hour of presentation. 1, 2

• Standard regimen: Vancomycin + ceftriaxone (or cefotaxime) 1, 2
• Add ampicillin for patients >50 years old or with risk factors for Listeria monocytogenes (immunocompromised, alcoholism, pregnancy) 2
• North American guidelines recommend vancomycin for all patients, while UK and European guidelines recommend vancomycin primarily for pneumococcal meningitis or areas with reduced cephalosporin susceptibility 2
• Dexamethasone 0.15 mg/kg IV every 6 hours should be administered before or simultaneously with the first antibiotic dose 1, 6, 2, 3

Neonates (0–3 Months)

For neonates, use ampicillin plus cefotaxime; avoid ceftriaxone due to the risk of fatal calcium-ceftriaxone precipitation. 6

• Standard regimen: Ampicillin + cefotaxime 6
• Never use ceftriaxone in neonates 6
• Common pathogens: Streptococcus agalactiae (group B streptococcus) and Escherichia coli 1

Children (3 Months–18 Years)

For children beyond 3 months, use vancomycin plus ceftriaxone (or cefotaxime) in regions with high pneumococcal resistance. 6

• Standard regimen: Vancomycin + ceftriaxone (or cefotaxime) 6
• Dexamethasone 0.15 mg/kg IV every 6 hours should be given immediately before or with the first antibiotic dose 6
• Continue dexamethasone for 4 days if pneumococcal meningitis is confirmed; stop if viral or tuberculous etiology is identified 6

Fluid Resuscitation in Septic Presentation

If shock signs are present (tachycardia, prolonged capillary refill >2 seconds, hypotension, altered consciousness), give 20 mL/kg isotonic crystalloid or colloid bolus rapidly, reassessing after each bolus. 6

• Up to 60 mL/kg may be required within the first hour for severe meningococcal sepsis 6
• When >40 mL/kg is needed or the patient remains unstable, consult pediatric intensive care immediately 6

Pathogen-Specific Therapy

Streptococcus pneumoniae (Pneumococcus)

• Most common cause of bacterial meningitis in adults and children beyond neonatal age 1, 5
• Empiric: Vancomycin + ceftriaxone (or cefotaxime) 1, 2
• Confirmed susceptible: Ceftriaxone or cefotaxime alone 9
• Penicillin-resistant: Continue vancomycin + ceftriaxone 2
• Dexamethasone provides greatest benefit in pneumococcal meningitis 6, 2, 3

Neisseria meningitidis (Meningococcus)

• Second most common cause in adults and children 1, 5
• Serogroup B now predominates in many countries 1
• Empiric: Ceftriaxone or cefotaxime 9
• Confirmed: Penicillin G or ceftriaxone 9

Listeria monocytogenes

• Third most common cause in adults, associated with age >50 years and immunocompromise 1, 2
• Empiric (when suspected): Ampicillin (or benzylpenicillin) + gentamicin 2
• Cephalosporins are ineffective against Listeria 9

Haemophilus influenzae

• Now rare due to vaccination; occurs in unvaccinated children or non-type b serotypes 1
• Empiric: Ceftriaxone or cefotaxime 9

Group B Streptococcus (Streptococcus agalactiae)

• Leading cause of neonatal meningitis 1
• Empiric: Ampicillin + cefotaxime (neonates) 6

Escherichia coli

• Second leading cause of neonatal meningitis 1
• Empiric: Ampicillin + cefotaxime (neonates) 6
• Confirmed: Cefotaxime, ceftriaxone, or ceftizoxime 9

Gram-Negative Bacilli (Enterobacteriaceae)

• Empiric: Ceftriaxone, cefotaxime, or ceftizoxime 9
• Failures have occurred with Enterobacter spp. and Serratia marcescens 9

Pseudomonas aeruginosa

• Only ceftazidime yields adequate CSF concentrations 9

Viral Meningitis Management

Viral meningitis is generally self-limited and requires supportive care; empiric acyclovir should be started if herpes simplex virus (HSV) encephalitis cannot be excluded. 1, 3

• Most cases are caused by enteroviruses and have a good prognosis 3
• CSF typically shows lymphocytic predominance, normal glucose, and mildly elevated protein 4
• Start empiric acyclovir if HSV encephalitis is a consideration (altered mental status, focal neurological signs, temporal lobe abnormalities on imaging) 1
• Viral PCR (enterovirus, HSV, VZV) should be sent on CSF 1
• Supportive care includes analgesia, antiemetics, and hydration 3

Adjunctive Dexamethasone Therapy

Dexamethasone 0.15 mg/kg IV every 6 hours should be administered before or simultaneously with the first antibiotic dose in all patients with suspected bacterial meningitis. 1, 6, 2, 3

• Continue for 4 days if bacterial meningitis is confirmed 1, 6
• Discontinue if viral or tuberculous meningitis is identified 6
• Greatest benefit is seen in pneumococcal and H. influenzae type b meningitis 6, 2
• Dexamethasone reduces mortality and morbidity in pneumococcal meningitis 2, 3

Preventive Vaccinations

All survivors of bacterial meningitis should receive pneumococcal vaccination to reduce the risk of recurrence. 6

• Pneumococcal conjugate vaccines (PCV10, PCV13) have reduced incidence in both children and adults through herd immunity 1
• Meningococcal C conjugate vaccine has dramatically reduced serogroup C disease 1
• Meningococcal B vaccine is now available in some countries 1
• H. influenzae type b vaccine has nearly eliminated Hib meningitis in vaccinated populations 1
• Group B streptococcus maternal vaccination is under study to prevent neonatal disease 1

Contact Prophylaxis

Offer chemoprophylaxis within 24 hours of diagnosis to household members and close contacts of cases caused by N. meningitidis or H. influenzae type b. 6, 3

• Close contacts include household members, shared sleeping quarters, and kissing contacts 6
• Rifampicin is the standard prophylactic agent (dose adjusted by age) 6, 3
• Ciprofloxacin or ceftriaxone may be used as alternatives when rifampicin is contraindicated 6, 3
• Prophylaxis is not routinely indicated for contacts of pneumococcal meningitis 6, 3

Follow-Up and Long-Term Sequelae

Hearing assessment should be performed within 4 weeks of discharge; sensorineural hearing loss occurs in 10–30% of pediatric bacterial meningitis survivors. 6

• Routine audiologic evaluation is recommended for all survivors 6
• Screen for neuropsychological sequelae (cognitive deficits, behavioral problems) at 3–6 months post-illness 6
• Provide pneumococcal vaccination to all survivors 6

Critical-Care Transfer Criteria

Transfer to intensive care immediately if any of the following are present: 6

• Rapidly evolving purpuric rash (suggestive of meningococcal sepsis)
• Glasgow Coma Scale ≤12
• Cardiovascular instability requiring >40 mL/kg fluid resuscitation
• Respiratory compromise (hypoxia or increased work of breathing)
• Prolonged or recurrent seizures

Treatment Algorithm

Step 1: Immediate Recognition (Within Minutes)

• Suspect meningitis if fever + headache + neck stiffness, altered mental status, or purpuric rash 1, 5
• Remember: Classic triad present in only 44–51% of cases 4, 5

Step 2: Immediate Actions (Within 1 Hour)

• Obtain blood cultures immediately 4, 6, 2
• Assess for contraindications to lumbar puncture 1, 4, 6
• If contraindications present (GCS ≤10–12, focal deficits, recent seizure, immunocompromise, shock, coagulopathy): start antibiotics immediately and defer LP 4, 6
• If no contraindications: perform lumbar puncture without delay 1, 4, 2
• Start empiric antibiotics + dexamethasone within 1 hour 1, 6, 2

Step 3: Empiric Antibiotic Selection

• Neonates (0–3 months): Ampicillin + cefotaxime 6
• Children (3 months–18 years): Vancomycin + ceftriaxone (or cefotaxime) 6
• Adults (<50 years, immunocompetent): Vancomycin + ceftriaxone (or cefotaxime) 1, 2
• Adults (≥50 years or immunocompromised): Vancomycin + ceftriaxone + ampicillin 2
• All ages: Dexamethasone 0.15 mg/kg IV q6h before or with first antibiotic dose 1, 6, 2

Step 4: CSF Interpretation

• If any high-certainty criterion met (CSF glucose <34 mg/dL, CSF/plasma glucose <0.23, CSF protein >120 mg/dL, CSF WBC >12,000, CSF neutrophils >11,000): Confirm bacterial meningitis and continue antibiotics 4
• If CSF glucose >2.6 mmol/L and CSF/plasma glucose >0.36: Bacterial meningitis unlikely; consider viral etiology 4
• If lymphocytic predominance with normal glucose/protein: Consider viral meningitis but do not stop antibiotics until bacterial etiology excluded 7

Step 5: Pathogen-Specific Adjustment

• Adjust antibiotics based on Gram stain, culture, and PCR results 1, 2
• Continue dexamethasone for 4 days if pneumococcal meningitis confirmed 6, 2
• Stop dexamethasone if viral or tuberculous meningitis identified 6

Step 6: Supportive Care and Monitoring

• If shock present: 20 mL/kg boluses up to 60 mL/kg in first hour 6
• Transfer to ICU if GCS ≤12, >40 mL/kg fluids needed, respiratory compromise, or recurrent seizures 6
• Manage elevated intracranial pressure using neurocritical care strategies 5

Step 7: Follow-Up

• Hearing assessment within 4 weeks 6
• Neuropsychological screening at 3–6 months 6
• Pneumococcal vaccination for all survivors 6
• Contact prophylaxis within 24 hours for meningococcal or Hib cases 6, 3