**Core Concept**
The management of latent tuberculosis (TB) infection in infants exposed to TB involves chemoprophylaxis with isoniazid (INH) to prevent the progression to active TB disease. After completing a course of INH, further management is essential to assess the effectiveness of treatment and identify any potential issues.

**Why the Correct Answer is Right**
After 3 months of INH chemoprophylaxis, a tuberculin skin test (TST) or an interferon-gamma release assay (IGRA) is performed to assess the response to treatment. This is crucial as it helps to identify individuals who have developed immunity to TB, indicating successful treatment. A negative test result suggests that the individual is no longer infected with TB.

**Why Each Wrong Option is Incorrect**
**Option A:** Continuing INH without testing would be inappropriate, as it may lead to unnecessary prolonged treatment and potential side effects.

**Option B:** Discontinuing INH without testing would be incorrect, as it would fail to assess the effectiveness of treatment and may miss individuals who have not responded to therapy.

**Option C:** Performing a chest X-ray without testing would be unnecessary, as it would not provide information on the immune response to TB and may not detect early changes in lung morphology.

**Option D:** Administering a different antitubercular medication without testing would be inappropriate, as it may not address the underlying infection and may lead to unnecessary exposure to additional medications.

**Clinical Pearl / High-Yield Fact**
It is essential to perform a follow-up test after chemoprophylaxis to assess the effectiveness of treatment and identify individuals who may require additional therapy or monitoring.

**Correct Answer:** B. Discontinue INH and perform a follow-up TST or IGRA.