Diagnosis

• Bacterial meningitis is primarily diagnosed by CSF examination. This is unnecessary with a classical meningococcal rash where the organism can be often cultured from the skin lesions. Lumbar puncture (LP) samples should be sent for urgent microscopy and culture, PCR, antigen virology, protein and glucose estimation (with concurrent plasma sample). Normal or lymphocytic CSF may be found in early pyogenic meningitis, especially L. monocytogenes.

• Raised ICP is common; unless confidently excluded, delay lumbar puncture (LP) but not antibiotics until after CT scanning. A normal CT scan does not completely exclude raised ICP.

• Empiric antibiotic therapy with concurrent steroids should be commenced immediately after taking blood cultures. The choice should be based on the patient's age. CSF cultures are positive in 50% if antibiotics are given compared to 60-90% in untreated cases.

• CSF bacterial antigen testing is available for most infecting organisms; sensitivity varies from 50-100% while specificity is high.

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