## Epidemiology of Bacterial Meningitis by Age and Region **Key Point:** *Streptococcus pneumoniae* is the **most common cause of community-acquired bacterial meningitis** in immunocompetent adults globally, including India. It accounts for 40–50% of cases in this age group. **High-Yield:** The epidemiology of bacterial meningitis varies by age, vaccination status, and geographic region. In India, *S. pneumoniae* and *N. meningitidis* are the two leading pathogens in adults. ### Age-Based Epidemiology of Bacterial Meningitis | Age Group | Most Common | Second Most Common | Notes | | --- | --- | --- | --- | | **Neonates (0–3 months)** | *E. coli* K1, *Group B Streptococcus* | *Listeria monocytogenes* | Ampicillin + cephalosporin | | **Infants & children (3 months–5 years)** | *S. pneumoniae*, *H. influenzae* | *N. meningitidis* | Hib vaccine reduces *H. influenzae* | | **Adults (18–50 years)** | *S. pneumoniae* | *N. meningitidis* | Pneumococcal vaccine recommended | | **Elderly (>50 years)** | *S. pneumoniae* | *Gram-negative rods*, *Listeria* | Higher mortality | | **Immunocompromised** | *Listeria*, *Gram-negative rods* | *Cryptococcus* (if CD4 <100) | Ampicillin essential | **Clinical Pearl:** *Neisseria meningitidis* typically presents with petechial/purpuric rash and can cause rapid fulminant meningococcemia. *S. pneumoniae* may have a more insidious onset but carries higher mortality in the elderly. **Mnemonic — SPiN (S. pneumoniae in adults):** **S**treptococcus **p**neumoniae is the **i**ncreased risk in **N**on-vaccinated or elderly populations.
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