Effect of BCG vaccination and non-tuberculous Mycobacterium infection on interferon gamma specific assay and a tuberculin skin test among children with a tuberculosis contact in Surabaya, Indonesia

The tuberculin skin test (TST) as a diagnostic tool for tuberculosis (TB) infection is used in many countries, including Indonesia, but lacks specificity. Interferon-gamma is a highly specific assay because it is not influenced by previous BCG vaccination or non-tuberculous mycobacteria (NTM) infections. We aimed to study the effect of BCG vaccination and NTM infection on the results of the interferon-gamma specific assay and TST among children with a TB contact. We carried out a cross-sectional study of children at an outpatient clinic in Surabaya, Indonesia. We studied 37 children aged 1-15 years having a household contact with an acid-fast bacilli positive adult index case. BCG vaccination was determined by the presence of a BCG scar. A PPD RT23 2 tuberculin test was used for the TST. ESAT-6, CFP-10, and TB 7.7(p4) antigens were used for the interferon-gamma assay by ELISA. Gastric aspirates were cultured in Lowenstein-Jensen media. A comparison of the two diagnostic tools among children aged 1-5 years without a BCG scar, revealed high agreement, while children with a BCG scar it revealed disagreement. Among children aged5 years with or without a BCG scar the comparisons revealed disagreement. Among children aged5-10 years, a comparison of the two diagnostic tools among NTM positive and negative children, there was a disagreement in results. Among children aged 1-5 years, the TST was influenced by a BCG scar. Infection with NTM had no influence on the results of the TST among children aged5-10 years, while in children aged 1-5 years and10 years the results could not be determined in this study.