Meningitis - Introduction, Risk Factors, Transmission, Etiological agents

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:

1. Hematogenous spread

2. Direct spread from an infected site

3. Anatomic defects in CNS structure

4. 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)

In chronic meningitis, the most common causative agents are

• M. tuberculosis

• Nocardia spp.

• Actinomycetes

• Treponema pallidum

• Brucella

• Borrelia burgdorferi

Results of meningitis

The results/pathological changes in meningitis are as follows:

• CSF => cloudy (bacterial)

• clear (viral)

• Elevated WBC

• Elevated protein

• Decreased glucose (bacterial)

• Elevated CSF pressure