Case 04: Headache and Fever (Meningitis)

A 19-year-old university student presents to the emergency department with a 12-hour history of severe headache, high fever (39.8°C), and marked neck stiffness. Her flatmate reports she seemed confused earlier. On examination she has a non-blanching petechial rash on her legs, photophobia, and a positive Kernig's sign. Bacterial meningitis is suspected.

Meningitis is inflammation of the meninges — the three membranes (dura mater, arachnoid mater, pia mater) covering the brain and spinal cord. The classical triad is fever, headache, and neck stiffness. Bacterial meningitis (most severe) typically presents with this triad plus photophobia, phonophobia, altered consciousness, and the characteristic non-blanching petechial or purpuric rash of meningococcal septicaemia. Viral meningitis is milder, self-limiting, and rarely produces a rash.

In young adults, the most common causative organisms are Neisseria meningitidis (meningococcus) and viral agents (herpes simplex, enteroviruses, mumps). In the elderly and immunocompromised, Streptococcus pneumoniae, Listeria monocytogenes, gram-negative bacteria, and Cryptococcus neoformans (in HIV/AIDS) predominate.

Microorganisms enter the CSF via three routes: (1) crossing nasopharyngeal epithelium into the blood (haematogenous spread — the most common route for N. meningitidis), (2) contiguous spread from a local infection such as otitis media or sinusitis, or (3) direct inoculation through trauma or surgery. Once in the subarachnoid space, bacteria trigger a vigorous inflammatory response: cytokines increase vascular permeability, disrupt the blood–brain barrier, and cause cerebral oedema, raising intracranial pressure (ICP). Raised ICP manifests as headache, vomiting, papilloedema, and ultimately herniation.

Kernig's sign: with the patient supine, the hip is flexed to 90 degrees; resistance or pain on extending the knee beyond 135 degrees indicates irritated meninges stretching inflamed nerve roots. Brudzinski's sign: passive neck flexion causes involuntary hip and knee flexion due to meningeal irritation along the spinal column. Both signs have low sensitivity (~5–30%) but high specificity (~95%); a negative result does not exclude meningitis.

Pre-hospital treatment (suspected case): IV or IM ceftriaxone 2 g for adults (100 mg/kg for children), or benzylpenicillin 2.4 g. Hospital treatment is guided by organism: empirical IV ceftriaxone; then N. meningitidis — IV ceftriaxone; S. pneumoniae — IV penicillin (vancomycin + ceftriaxone if resistant). Prophylaxis for close contacts (those with >8 hours contact, household members, those sharing oral secretions): rifampicin, ciprofloxacin, or ceftriaxone IM 250 mg, given within 24 hours of diagnosis.

The distinction between therapeutic and prophylactic treatment is critical: the therapeutic target is blood and CSF (IV ceftriaxone penetrates the BBB), whereas the prophylactic target is the nasopharynx (rifampicin, ciprofloxacin, and IM ceftriaxone achieve nasopharyngeal eradication). Cases of meningococcal disease are notifiable to the local Medical Officer of Health for epidemiological surveillance and contact tracing.

Diagnostic test interpretation requires understanding of sensitivity (proportion of true positives correctly identified — Sn = A/(A+C)) and specificity (proportion of true negatives correctly identified — Sp = D/(B+D)), as well as positive and negative predictive values (PPV and NPV), which are prevalence-dependent. High pre-test probability (e.g., in a high-incidence region or Maori/Pacific population for meningococcal disease) shifts the PPV upward even for tests with moderate sensitivity.