Use of purified protein derivative to assess the risk of infection in children in close contact with adults with tuberculosis in a population with high Calmette-Guérin bacillus coverage

Abstract

Setting: Household contacts <15 years of age of adults with tuberculosis (TB) attending a reference center in Aracaju, Sergipe, Northeast Brazil.

Objective: To assess the use of purified protein derivative (PPD) and frequency of infection in children with high Calmette-Guérin bacillus (BCG) coverage who were recently exposed to TB.

Design: Cross-sectional study of 141 exposed household contacts <15 years of age and 506 nonexposed neighborhood controls. Children were examined and assessed for degree of exposure to index cases, BCG vaccination and scar and were tested with PPD.

Results: Exposed children were younger and less up to date in their vaccination schedule than controls (P < 0.05). BCG had been given to 95.6% of exposed children and 97.4% of controls, but only 80.9% of exposed vs. 88.5% of controls had a scar (P < 0.05). Scar sizes of exposed children were smaller (medians, 4.5 and 7 mm, respectively; P < 0.05). Children had lower weight for age z scores and height than the National Center for Health Statistics standards. Exposed children had lower weight for age z scores than controls (P < 0.05). Sixty-seven (47.5%) exposed children and 18 (3.6%) controls had PPD readings of >10 mm. Positivity and induration sizes increased with age, although this was significant only in the controls. The presence of a BCG scar was not associated with having a positive PPD. The degree of exposure was an important factor for PPD positivity; 66 (60.6%) of the 109 children with close exposure were positive compared with 1 (3.1%) of 32 with less intimate exposure. PPD indurations among close contacts were also larger than those with restricted exposure and controls (16.3, 11 and 9.4 mm, respectively; P < 0.05). PPD positivity was associated with the quantification of acid-fast bacilli in the adult; 38.5% of contacts with adults with sputum with (+) were positive, compared with 42.3% of those with (++) and 58.4% with (+++) (P < 0.05).

Conclusion: PPD is a useful test to identify children infected with TB independently of whether they had received BCG or not. Children exposed to adults with TB are at high risk of infection. The risk of infection is associated with the intimacy of contact and the number of bacilli expectorated in sputum.