Correlation between Bacillus Calmette–Guérin Scar Formation and Tuberculin Skin Test in Infants

Abstract Background: The presence of a Bacillus Calmette–Guérin (BCG) scar is often used as a marker of successful vaccination; however, its association with tuberculin skin test (TST) positivity in infants remains inconsistent and not fully understood. Objectives: To determine the correlation of BCG scar and TST in the infants after BCG immunization. Methods: We conducted a retrospective cohort study as a secondary data analysis using data from the previous study titled “Safety and Tuberculin Conversion Following BCG Moscow Strain Vaccination Compared to BCG Pasteur Strain in Indonesian Infants”. The intervention study was conducted at the Department of Child Health, Faculty of Medicine, Universitas Udayana/Ngoerah Hospital, Denpasar, Bali, Indonesia, during the period of January-July 2012. A total of 220 healthy infants aged 0–1 month were enrolled between January and July 2012, as part of a randomized trial comparing BCG Moscow and Pasteur strains. Results: A total of 205 out of 220 infants completed the study. Of 205 infants, 134 (65.4%) developed BCG scars , while 71 (34.6%) had no visible scar formation. Scarring occurred in 60.2% of girls and 66.7% of boys, with no significant difference ( P = 0.342). The incidence of scarring in all well-nourished infants was 63.9%. The incidence of a positive TST in this study was reported as 24.5% for group A (BCG Moscow Strain Vaccination) and 29.1% for group B (BCG Pasteur Strain). BCG scar formation was evaluated at the sixth follow-up visit (K-6), approximately 90 days postimmunization. At this visit, TST was administered, and induration was measured after 48–72 h. The association between scar formation and TST positivity was analyzed using Spearman’s rank correlation ( r = 0.144, P = 0.039). Conclusion: This study demonstrated a statistically significant, but very weak, correlation between BCG scar formation and TST positivity in infants. Although the majority of infants developed BCG scars after vaccination, scar formation was poorly associated with TST response. These findings indicate that BCG scar presence reflects vaccine administration rather than tuberculin reactivity, and therefore cannot be used as a reliable marker of immune response as measured by TST. These findings suggest that while the BCG scar is a useful marker for vaccination, it is not strongly associated with TST positivity, highlighting the limited cross-reactivity between BCG-induced immunity and TST results.