A 9-month-old female infant born to parents from a tuberculosis-endemic region presents for routine immunisation. She received BCG at birth (visible scar present). On examination, she has a firm, non-tender axillary lymph node (1 cm) and is otherwise healthy with no constitutional symptoms. Her tuberculin skin test (TST) is 12 mm induration. According to the National Immunisation Schedule and IAP guidelines, what is the most appropriate next step regarding her immunisation status?

Explanation

## TST Positivity Post-BCG and Immunisation Safety ### Clinical Context The infant has: - BCG vaccination at birth (scar present) - TST induration 12 mm at 9 months - Asymptomatic, no constitutional symptoms - No respiratory signs or contact history mentioned ### Interpretation of TST in BCG-Vaccinated Infants **Key Point:** **BCG vaccination induces TST positivity in 50–90% of vaccinated infants**, which can persist for years. TST positivity alone in a BCG-vaccinated, asymptomatic infant does NOT indicate active tuberculosis disease. ### Distinguishing Active TB from BCG-Induced TST | Feature | Active TB Disease | BCG-Induced TST | |---|---|---| | **Clinical symptoms** | Fever, cough, weight loss, night sweats | Absent | | **Constitutional signs** | Present | Absent | | **Lymph node characteristics** | Often matted, draining, tender | Firm, non-tender, isolated | | **Chest X-ray** | Infiltrates, cavitation, hilar lymphadenopathy | Normal | | **TST size** | Variable (often >15 mm) | Can be 5–20 mm | | **Contact history** | Often present | May be absent | **Clinical Pearl:** A **firm, non-tender, isolated lymph node in an asymptomatic BCG-vaccinated infant with TST 12 mm is consistent with BCG lymphadenitis (benign, self-limiting)**, not active tuberculosis. ### Immunisation Approach **High-Yield:** According to IAP and National Immunisation Schedule: - **Live vaccines (Measles, OPV, Rotavirus) can be safely administered to asymptomatic, BCG-vaccinated infants with TST positivity** - TST positivity is NOT a contraindication to live vaccines in the absence of clinical or radiological evidence of active TB - Deferring vaccines in such cases delays protection against vaccine-preventable diseases **Mnemonic: "BCG-TST Rule"** — **B**CG vaccination → **C**auses **T**ST positivity; **S**ymptomatic or **T**B-active disease must be ruled out before deferring vaccines. ### Why Option 2 is Correct The infant is asymptomatic, has no constitutional symptoms, and the axillary lymph node is consistent with benign BCG lymphadenitis. TST positivity in a BCG-vaccinated infant is expected and does not contraindicate live vaccines. Measles vaccine should be administered on schedule.