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 ?
**Core Concept**
The question is testing the student's knowledge of bacterial meningitis, specifically the likely causative agent in a 10-month-old child presenting with symptoms of acute bacterial meningitis, including basal exudates and hydrocephalus on cranial CT scan.
**Why the Correct Answer is Right**
The correct answer is likely to be *Haemophilus influenzae type b (Hib)*. This bacterium is a common cause of bacterial meningitis in infants and young children, particularly in the context of basal exudates and hydrocephalus. Hib produces a polysaccharide capsule that allows it to evade the host's immune system, leading to severe infection. The presence of basal exudates and hydrocephalus suggests a severe and fulminant course of the disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** *Streptococcus pneumoniae* is another common cause of bacterial meningitis, but it is less likely in this scenario given the patient's age and the presence of basal exudates and hydrocephalus.
* **Option B:** *Neisseria meningitidis* is a leading cause of bacterial meningitis in children and adolescents, but it is more commonly associated with a more acute and severe presentation, often with petechial rash.
* **Option C:** *Escherichia coli* is a cause of bacterial meningitis in neonates and young infants, but it is less common in this age group and is often associated with a more complex clinical picture.
**Clinical Pearl / High-Yield Fact**
In infants and young children presenting with symptoms of bacterial meningitis, it is essential to consider the possibility of Hib infection, particularly in the context of basal exudates and hydrocephalus. Early recognition and treatment are critical to prevent long-term sequelae and improve outcomes.
**Correct Answer:** D. *Haemophilus influenzae type b (Hib)*