A 28-year-old man presents with acute onset of fever, headache, neck stiffness, and petechial rash on the trunk. CSF analysis shows pleocytosis with predominant neutrophils, elevated protein, and low glucose. Gram stain of CSF reveals gram-negative diplococci. What is the most common cause of bacterial meningitis in this age group in India?

## Epidemiology of Bacterial Meningitis by Age **Key Point:** Neisseria meningitidis is the most common cause of bacterial meningitis in adolescents and young adults (15–40 years) in most developed and developing countries, including India. ### Clinical Presentation The patient's presentation is classic for meningococcal meningitis: - Acute fever with headache and neck stiffness - **Petechial or purpuric rash** — a hallmark feature that distinguishes meningococcal disease - CSF findings: neutrophilic pleocytosis, elevated protein, low glucose (typical of bacterial meningitis) - Gram-negative diplococci on Gram stain ### Age-Related Epidemiology | Age Group | Most Common Organism | Second Most Common | | --- | --- | --- | | Neonates (0–3 months) | E. coli K1, Group B Streptococcus | Listeria monocytogenes | | Infants & children (3 months–5 years) | Streptococcus pneumoniae | Neisseria meningitidis | | Adolescents & young adults (15–40 years) | **Neisseria meningitidis** | Streptococcus pneumoniae | | Elderly (>50 years) | Streptococcus pneumoniae | Listeria monocytogenes | **High-Yield:** The presence of a petechial or purpuric rash in meningitis is virtually pathognomonic for meningococcemia and strongly suggests N. meningitidis. ### Organism Characteristics - Gram-negative diplococci (kidney or coffee-bean shaped) - Oxidase-positive - Ferments glucose and maltose (unlike N. gonorrhoeae, which ferments only glucose) - Polysaccharide capsule (serogroups A, B, C, W, Y) - Endotoxin-mediated tissue damage → petechial rash, DIC, septic shock **Clinical Pearl:** Meningococcal meningitis can rapidly progress to septic shock with DIC and multi-organ failure. Early recognition and empiric therapy with ceftriaxone or cefotaxime (with vancomycin in penicillin-resistant regions) is life-saving. **Mnemonic — Meningococcal Rash:** **PETECHIAE** = Purpura, Endotoxin-driven, Thrombosis, Endothelial injury, Coagulopathy, Hemorrhage, Acute, Inflammatory, Exanthem. [cite:Park 26e Ch 8]