What are the next steps for a 2-year-old child, born in one location and migrating to another, with no visible BCG (Bacillus Calmette-Guérin) scar, but a reported history of BCG vaccination, during a physical examination prior to migration?

Management of a 2-Year-Old with Reported BCG Vaccination but No Visible Scar

Accept the maternal report of BCG vaccination as valid and proceed with tuberculin skin testing (TST) to screen for latent tuberculosis infection, since the absence of a BCG scar does not exclude prior vaccination and should not alter your clinical approach. 1

Why the Absence of BCG Scar is Clinically Irrelevant

• BCG scars are not universally present even after documented vaccination, and their absence does not indicate lack of immunization 1
• The presence or absence of a scar has no bearing on the interpretation of tuberculosis screening tests or the child's immune status 1
• BCG coverage in children from high-burden countries ranges from 60-90%, making prior vaccination highly plausible regardless of scar visibility 1

Recommended Screening Approach for This 2-Year-Old

Perform a tuberculin skin test (TST) as the primary screening tool for latent tuberculosis infection in this age group. 1

Age-Specific Testing Rationale

• For children under 5 years of age, most international guidelines prefer TST alone rather than interferon-gamma release assays (IGRAs), as data on IGRA performance in very young children remain limited 1
• The WHO, ECDC, France, Brazil, and Switzerland all recommend TST alone for children in this age range 1
• While the 2017 ATS/IDSA/CDC guidelines extend IGRA use down to age 5, they acknowledge that TST remains an acceptable alternative, especially when IGRA is not available or too costly 1

TST Interpretation in BCG-Vaccinated Children

Interpret any TST induration ≥10 mm as positive and indicative of possible M. tuberculosis infection, regardless of BCG vaccination history. 1

• The CDC explicitly states that "a positive TST in a foreign-born or BCG-vaccinated person should be interpreted as evidence of recent M. tuberculosis infection in contacts of persons with infectious cases" 1
• BCG-induced tuberculin sensitivity can persist for up to 10 years after vaccination at birth, and even longer with revaccination 1
• However, the clinical priority is to not miss true tuberculosis infection, which carries significant morbidity and mortality risk in children under 5 years old 1

Alternative IGRA Approach (If Resources Permit)

If you choose to use an IGRA instead of or in addition to TST:

• IGRAs have superior specificity compared to TST in BCG-vaccinated children (>95% vs 60% for TST), as they are not confounded by prior BCG vaccination 1, 2
• Recent evidence suggests IGRAs are acceptable even in children under 2 years: across 575 high-risk children under age 2 with negative IGRA results, zero progressed to active tuberculosis disease, including 70 who were TST-positive but IGRA-negative 3
• A two-step approach (TST followed by IGRA if TST positive) maximizes specificity while maintaining sensitivity, particularly useful in BCG-vaccinated children from high-burden countries 1

Critical Next Steps After Testing

If TST is Positive (≥10 mm induration):

1. Obtain chest radiograph to exclude active pulmonary tuberculosis 1
2. Assess for symptoms of active disease: fever, night sweats, weight loss, chronic cough, failure to thrive 1
3. If chest X-ray is normal and no symptoms present, diagnose latent tuberculosis infection (LTBI) and initiate preventive therapy 1
4. Recommended LTBI treatment regimen: 6 months of isoniazid (10-15 mg/kg/day, maximum 300 mg) or 3 months of rifampin plus isoniazid 4

If TST is Negative:

• No further action required unless there is known recent exposure to an infectious tuberculosis case 1
• If recent exposure exists, repeat TST in 8-10 weeks to detect delayed conversion 1

Key Clinical Pitfalls to Avoid

• Do not dismiss a positive TST as "just BCG" in a child from a high-burden country—the risk of true infection is substantial and the consequences of missing it are severe (disseminated or meningeal tuberculosis) 1
• Do not delay testing or treatment based on scar absence—maternal history is sufficient documentation of vaccination status 1
• Do not use the two-step TST procedure (used in serial testing programs) for contact investigation, as a positive second test after initial negative should be classified as recent infection 1
• Children under 5 years have the highest risk of progression to severe tuberculosis (disseminated and meningeal disease), making early detection and treatment of LTBI critical 1