**Question:** A 10 month old child presents with two weeks history of fever, vomiting and alteration of sensorium. Cranial CT scan reveals basal exudates and hydrocephalus, the most likely etiological agent is –

A. Neisseria meningitidis
B. Streptococcus pneumoniae
C. Haemophilus influenzae
D. Escherichia coli

**Correct Answer:** **D. Escherichia coli**

**Core Concept:** Meningitis is an inflammation of the protective membranes (meninges) covering the brain, and spinal cord. The most common causes of bacterial meningitis in children are:

1. **Neisseria meningitidis:** A common cause of meningitis, especially in infants and young children.
2. **Streptococcus pneumoniae:** A common cause of bacterial meningitis, particularly in children with underlying respiratory illnesses.
3. **Haemophilus influenzae:** A common cause of bacterial meningitis, particularly in young children, but is less common now with the widespread use of Hib vaccines.
4. **Escherichia coli (E. coli):** Although less common than the previous three, it is a significant cause of bacterial meningitis in children, especially in those with urinary tract infections (UTIs) or bacteremia (bloodstream infections).

**Why the Correct Answer is D:**

Escherichia coli (E. coli) is the most likely etiological agent in this case because the child has a history of fever, vomiting, and alteration of sensorium, which indicates a severe infection. Additionally, the presence of basal exudates on the cranial CT scan suggests an acute bacterial meningitis.

**Why each wrong answer is incorrect:**

1. **Neisseria meningitidis:** Although it is a cause of meningitis, it is less likely in this case due to the child's age and the presence of UTI symptoms.
2. **Streptococcus pneumoniae:** Although a cause of meningitis, the child's age and absence of respiratory symptoms make this less likely.
3. **Haemophilus influenzae:** Similar to option 1, it is less likely due to the child's age and the presence of UTI symptoms.

**Clinical Pearl:** Understanding the clinical presentation, the age of the child, and the association of the symptoms with underlying infections (e.g., UTI) can help narrow down the etiological agents leading to meningitis. In this case, the child's age and UTI symptoms strongly point towards E. coli as the most likely causative agent, despite it being less common in this age group. This knowledge can aid in appropriate treatment and management of the child, as E. coli meningitis requires specific antibiotic treatment and supportive care.