Write a short note on acute bacterial (pyogenic) meningitis.

Definition & Aetiology

Acute bacterial meningitis is purulent inflammation of the meninges and subarachnoid space, a medical emergency with mortality of 10–30% and a high rate of neurological sequelae in survivors. Outcome depends almost entirely on how quickly antibiotics are given.

Predisposing factors: otitis media, sinusitis, mastoiditis, pneumonia, endocarditis, head injury with CSF leak, splenectomy, alcohol excess, diabetes, HIV and other immunosuppression, and crowded living conditions.

Clinical Features

Classic triad — fever, neck stiffness and altered mental state. Note that all three are present in fewer than half of patients; almost all have at least two of fever, headache, neck stiffness and altered consciousness.

• Symptoms: fever, severe headache, photophobia, nausea and vomiting, neck pain, drowsiness, confusion, irritability.
• Meningeal signs: neck stiffness, Kernig's sign (pain and resistance on extending the knee with the hip flexed), Brudzinski's sign (passive neck flexion causes hip and knee flexion). These are insensitive and may be absent in the very young, the elderly and the immunosuppressed.
• Raised intracranial pressure: deteriorating consciousness, papilloedema, bradycardia with hypertension, vomiting, cranial nerve palsies (III and VI).
• Seizures in about 25%; focal neurological deficits from vasculitis, infarction or subdural collection.
• Meningococcal disease: non-blanching petechial or purpuric rash, rapidly progressive septic shock, disseminated intravascular coagulation, and Waterhouse–Friderichsen syndrome (bilateral adrenal haemorrhage with adrenal failure). Meningococcaemia can kill within hours.
• In infants: poor feeding, high-pitched cry, bulging fontanelle, hypotonia, hypothermia rather than fever, and no neck stiffness.

Investigations

• Blood cultures immediately — before antibiotics, but antibiotics must never be delayed to obtain them or to perform imaging.
• Lumbar puncture — the definitive investigation. CT head first only if there are focal neurological signs, papilloedema, new seizures, GCS below 10, severe immunosuppression, or suspicion of a mass lesion; otherwise proceed directly.
• CSF findings in pyogenic meningitis: turbid or frankly purulent, opening pressure raised, neutrophilic pleocytosis (often > 1000/µL), markedly raised protein, and very low glucose (CSF:blood ratio < 0.4). Send for Gram stain (positive in 60–80% before antibiotics), culture and sensitivity, and bacterial antigen or multiplex PCR where available (particularly useful after antibiotics have been started).
• Bloods: CBC, CRP, procalcitonin, renal and liver function, glucose (paired with CSF glucose), coagulation profile, and blood cultures.
• Imaging: CT or MRI to identify complications — hydrocephalus, abscess, subdural empyema, venous sinus thrombosis, infarction.
• Look for the source: ENT examination, chest X-ray, and skin lesion aspirate in meningococcaemia.

Management

1. Antibiotics — the single determinant of outcome

• Give empirical intravenous antibiotics IMMEDIATELY on clinical suspicion, ideally within an hour, and certainly before CT and before lumbar puncture if these will cause any delay.
• Empirical therapy typically comprises a third-generation cephalosporin (ceftriaxone or cefotaxime), with vancomycin added where penicillin-resistant pneumococcus is a concern, and ampicillin added for *Listeria* in the elderly, pregnant and immunosuppressed.
• Rationalise once culture and sensitivity are available; duration depends on organism.

2. Dexamethasone

Adjunctive dexamethasone, given with or just before the first antibiotic dose, reduces mortality and, in particular, hearing loss and neurological sequelae in pneumococcal meningitis. It is of no benefit if started after antibiotics.

3. Supportive and intensive care

• Airway protection and ventilation for depressed consciousness; fluid resuscitation and vasopressors for septic shock.
• Manage raised intracranial pressure — head elevation, mannitol, neurosurgical involvement for hydrocephalus.
• Control seizures; correct electrolyte disturbance (hyponatraemia from SIADH is common); manage DIC.
• Analgesia and antipyretics; nutritional support; DVT prophylaxis.

4. Public health measures — do not forget these

• Notify the case to public health authorities.
• Chemoprophylaxis for close household and intimate contacts of meningococcal (and *Haemophilus influenzae* type b) disease — with rifampicin, ciprofloxacin or ceftriaxone.
• Vaccination — meningococcal, pneumococcal and Hib vaccines for prevention, and specifically for asplenic patients, complement-deficient patients, and travellers to the meningitis belt and Haj pilgrims.

Complications

Acute: septic shock, DIC, cerebral oedema and herniation, hydrocephalus, seizures, cerebral infarction from vasculitis, subdural empyema, ventriculitis, SIADH.

Long-term: sensorineural hearing loss (the commonest sequel — arrange audiometry in all survivors, especially children), cognitive impairment, epilepsy, focal deficits, hydrocephalus and developmental delay.