The Most common cause of meningitis in children aged 5 years is
**Core Concept**
Meningitis is an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. In children, the most common causes of meningitis vary with age, but in those aged 5 years, a specific pathogen is predominantly responsible.
**Why the Correct Answer is Right**
The most common cause of meningitis in children aged 5 years is *Streptococcus pneumoniae*. This bacterium typically enters the body through the respiratory tract and can spread to the meninges, causing inflammation and infection. The pathogenesis involves the bacterium's ability to adhere to and invade the epithelial cells lining the respiratory tract, followed by its translocation to the meninges via the bloodstream.
**Why Each Wrong Option is Incorrect**
* **Option A:** Haemophilus influenzae type b (Hib) is a common cause of meningitis in children under 5 years of age, but its incidence has decreased significantly with the introduction of Hib vaccines.
* **Option B:** Neisseria meningitidis is a leading cause of meningitis in adolescents and young adults, not typically in children aged 5 years.
* **Option D:** Listeria monocytogenes can cause meningitis in neonates and immunocompromised individuals, but it is not the most common cause in children aged 5 years.
**Clinical Pearl / High-Yield Fact**
The introduction of conjugate vaccines against *Streptococcus pneumoniae* has significantly reduced the incidence of pneumococcal meningitis in children.
**Correct Answer:** C. Streptococcus pneumoniae.