Bacterial Meningitis I: Introduction

Bacterial meningitis is a severe, life-threatening inflammation of the meninges, particularly the pia mater and arachnoid mater, affecting the subarachnoid space, ventricles, and cerebrospinal fluid (CSF). If untreated, it can lead to significant neurological complications or death.

Causative Agents

Common pathogens vary with age and immune status. In adults, major organisms include Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. Streptococcus agalactiae (group B streptococcus, more common in neonates but possible in adults with risk factors). Other important causes include Listeria monocytogenes (in elderly and immunocompromised individuals), Mycobacterium tuberculosis, and non-typhoidal Salmonella. Predisposing factors include otitis media, sinusitis, pneumonia, and immunosuppression.

Transmission

Many causative bacteria, including meningococcus, pneumococcus, and H. influenzae, are often carried asymptomatically in the nasopharynx and spread via respiratory droplets or secretions. Group B streptococcus colonizes the gastrointestinal or genital tract and can be transmitted during childbirth.

Clinical Manifestations

Symptoms reflect systemic infection, meningeal irritation, and neurological involvement. Systemic features include fever, chills, and tachycardia. Meningeal signs include severe headache, photophobia, neck stiffness, and positive Kernig sign (pain on knee extension due to meningeal stretch) and Brudzinski sign (involuntary hip and knee flexion with neck flexion). Neurological features include altered consciousness, cranial nerve palsies, focal deficits, seizures, papilledema, and projectile vomiting in children with raised intracranial pressure.

Meningococcal meningitis may present with a petechial or purpuric rash. A severe complication, purpura fulminans, involves disseminated intravascular coagulation, skin necrosis, multi-organ failure, and possible death.