Meningitis — infection and inflammation of the meninges

Causes and types

Meningitis is usually classified by the principal cause. Viral (often called aseptic) meningitis is the most common overall and generally causes less severe illness, though exceptions occur. Bacterial meningitis is less common but more dangerous and requires urgent treatment. Common bacterial pathogens are those that can colonize the nose and throat and then invade the bloodstream or meninges; fungal and parasitic meningitis typically affect people with weakened immunity or following specific exposures.

• Viral: often milder, frequently due to enteroviruses and other community viruses.
• Bacterial: can progress rapidly and cause significant morbidity and mortality without prompt therapy.
• Fungal and parasitic: uncommon and usually associated with immune suppression or environmental risks.

Transmission and risk factors

Modes of transmission depend on the cause. Some bacterial forms spread between people through respiratory droplets or close contact and may be associated with asymptomatic carriage in the throat. Viral meningitis agents are often spread by fecal–oral or respiratory routes. Risk factors for meningitis include recent upper respiratory infection, skull fracture or neurosurgery, certain chronic medical conditions, immune suppression, and very young or advanced age. Because certain forms are contagious, many public-health agencies require notification of suspected cases to enable contact management and outbreak control.

Clinical features and diagnosis

Common symptoms in older children and adults include fever, severe headache, neck stiffness, sensitivity to light and changes in mental state. Infants and young children may present with nonspecific signs such as poor feeding, irritability, lethargy, vomiting or bulging fontanelle. Clinicians combine history and physical examination with laboratory and imaging tests to establish the cause and severity.

• Initial evaluation often includes blood tests and imaging when indicated.
• Definitive diagnosis usually requires analysis of cerebrospinal fluid obtained by lumbar puncture; laboratory findings help distinguish likely bacterial from viral causes.

Treatment

Management depends on the suspected or proven cause. Bacterial meningitis is treated urgently with appropriate intravenous antibiotics and often adjunctive corticosteroids in selected situations; viral meningitis may be managed with supportive care and specific antiviral drugs when a treatable virus is identified. Supportive measures include fluid and electrolyte management, pain control and treatment of complications such as seizures. Early recognition and rapid initiation of therapy greatly reduce the risk of death and long-term impairment.

Prevention and public-health measures

Prevention relies on vaccination, hygiene, prompt care for ear or sinus infections, and public-health interventions. Effective vaccines against some common bacterial causes have substantially lowered disease incidence in many countries. For certain bacterial cases, health authorities recommend antibiotic prophylaxis for close contacts and other measures to limit spread. Surveillance, reporting of notifiable infections and outbreak control are important components of public-health response.

Complications and outcomes

Meningitis can lead to serious and sometimes permanent complications, including hearing loss, cognitive and developmental problems, motor deficits, seizures and hydrocephalus. The risk of long-term sequelae is influenced by the causative agent, the patient’s age and health, and how quickly effective treatment begins. Rehabilitation and long-term follow-up are often necessary for survivors with sequelae.

Practical notes and guidance

1. Seek urgent medical assessment for suspected meningitis—early care improves outcomes.
2. Vaccination reduces the risk of several common bacterial forms; check local immunization guidance.
3. Health authorities may require reporting of suspected cases to enable contact tracing and public-health action.

For in-depth clinical recommendations, diagnostic criteria and local guidance, consult authoritative medical and public-health resources. The linked terms below provide orientation but do not replace professional evaluation: infections and meningitis, meningeal anatomy, central nervous system, meninx, microorganisms, viral causes and bacterial causes.