Meningitis - Introduction, Risk Factors, Transmission, Etiological agents

Last Modified: July 19, 2026 by Reshma Maharjan

Introduction to Meningitis

The brain and spinal cord are protected by 3 layers- The outer dura mater, the Middle arachnoid matter, and the Inner pia mater which are collectively known as meninges. Infection within the subarachnoid space or throughout the leptomeninges is called meningitis. The infection of the meninges, which is life-threatening, is known as meningitis.

CSF is present between the arachnoid mater and the pia mater.

Route of infection of Meningitis

Blood-brain barrier functions to maintain homeostasis (stable equilibrium) in the brain. In order for meninges to be infected Blood-brain barrier must be crossed. Primary routes of meningitis include:

Hematogenous spread
Direct spread from an infected site
Anatomic defects in CNS structure
Direct intraneural (travel along nerve leading to the brain)

Risk factors for Meningitis

The risk factors for meningitis includes:

Ear and sinus infections, mastoiditis
Age
Immune status of the patient
Alcoholism
Splenectomy
Diabetes mellitus
Prosthetic devices (ventriculoperitoneal shunts)

Etiological agents of Meningitis

The causative/etiological agents of meningitis include:

group B Streptococci (newborns)
E. coli
Listeria monocytogens
Haemophilus influenzae (cases have decreased in children of 4 months to 5 years due to immunization programs
Neisseria meningitidis (usually infects young adults due to crowded living spaces such as college dormitories, and military recruits)
Streptococcus pneunomiae (young children, eldery)
Pneumococci
Meningococci
Elizabethkingia meningoseptica (nosocomial infection, associated with nursery outbreaks)
S. aureus (less common)