**Core Concept**
Sudural effusion is a rare but characteristic complication of bacterial meningitis, most commonly seen in *Haemophilus influenzae* type b (Hib) infections, especially in young children. It results from inflammation of the dura mater leading to fluid accumulation beneath the dura, often due to increased intracranial pressure or direct bacterial invasion.

**Why the Correct Answer is Right**
*Haemophilus influenzae* type b (Hib) is the most common cause of bacterial meningitis in children under 5 years, and it is strongly associated with sudural effusion. This occurs due to the bacterium's ability to invade the meninges and cause localized inflammation, leading to dural irritation and subsequent fluid accumulation. The condition is more prevalent in immunocompromised or unvaccinated children and is a key feature in the clinical picture of Hib meningitis.

**Why Each Wrong Option is Incorrect**
Option B: *Neisseria meningitidis* typically causes meningitis with subarachnoid hemorrhage or petechial rash, not sudural effusion. It is associated with septic shock and rapid progression but lacks a strong link to dural effusion.
Option C: *Streptococcus pneumoniae* is a common cause of meningitis in adults and older children, but it is not specifically linked to sudural effusion. It tends to present with more systemic symptoms and less dural involvement.
Option D: *Enterococcus* is a rare cause of meningitis, usually in immunocompromised patients, and is not associated with sudural effusion or dural inflammation.

**Clinical Pearl / High-Yield Fact**
Sudural effusion is a hallmark sign of *Haemophilus influenzae* type b meningitis in children and is often seen on imaging. Vaccination against Hib has drastically reduced its incidence, making this a key point in preventive medicine.

✓ Correct Answer: A. H. influenza