Overview
Bacterial meningitis is an acute infection of the protective membranes (meninges) surrounding the brain and spinal cord. It results when invasive bacteria enter the bloodstream or respiratory tract and cross into the central nervous system. This condition typically develops fast, is a medical emergency, and can be fatal or cause severe long-term harm if not treated quickly with appropriate antibiotics. For general context see meningitis.
Causes and pathogenesis
A few species cause most cases; the responsible organism often depends on age, immune status and geography. Common pathogens include:
- Neisseria meningitidis (meningococcus)
- Streptococcus pneumoniae (pneumococcus)
- Haemophilus influenzae type b (Hib)
- Listeria monocytogenes (more common in neonates, elderly and immunocompromised)
After colonizing the nasopharynx or entering via another route, bacteria may invade the blood, cross the blood–brain barrier, and provoke intense inflammation of the meninges and cerebrospinal fluid (CSF). The inflammatory response increases intracranial pressure and can impair cerebral blood flow.
Signs, diagnosis and treatment
Typical symptoms include fever, severe headache, neck stiffness and altered mental status; other features can be photophobia, nausea, vomiting and seizures. In infants signs may be nonspecific, such as irritability, poor feeding or a bulging fontanelle.
Diagnosis relies on clinical examination plus laboratory testing of CSF obtained by lumbar puncture. Analysis usually assesses cell counts, glucose and protein levels, and seeks direct evidence of bacteria by Gram stain, culture or molecular tests (PCR). Because disease can progress rapidly, clinicians begin empiric intravenous antibiotics as soon as bacterial meningitis is suspected, then tailor therapy when the organism and sensitivities are known. Adjunctive corticosteroids are sometimes recommended in specific situations to reduce inflammation and complications.
Prevention and public health
Prevention strategies include routine immunization where available: meningococcal, pneumococcal and Hib vaccines have substantially reduced disease from those organisms. Close contacts of a case may be offered short-term antibiotic prophylaxis to reduce secondary transmission. Rapid identification, treatment and reporting are important to control outbreaks in communities, schools or other congregate settings.
Complications and prognosis
When treated promptly, many patients recover, but bacterial meningitis can leave permanent effects such as hearing loss, cognitive impairment, motor deficits or seizures. Outcomes depend on the causative organism, the patient’s age and health, and how quickly effective treatment begins. Public awareness, vaccination and early medical care remain the best defenses against severe outcomes.