Interpretation of the tuberculin skin test in bacille Calmette-Guerin vaccinated and nonvaccinated school children

Background: Our objective was to conduct a prevalence survey of purified protein derivative (PPD) reactions among Lebanese healthy school children to identify those with tuberculosis or latent tuberculosis and to investigate the effect of bacille Calmette-Guerin (BCG) vaccine on the interpretation of PPD reactivity. Methods: A self-administered questionnaire, including demographic characteristics, time of prior BCG vaccine and number of doses, known household contact with tuberculosis as well as parents' characteristics and living conditions was administered. PPD testing was performed on all children in diverse Lebanese regions aged 3 to 19 years. Reactivity that measured < 5 mm were considered negative induration, doubtful if between 5 and 9 mm and positive if 10 mm or above. Chest radiographs were obtained as part of the evaluation for children with positive induration. Results: Of 4895 children, 4271 entered into the final data analysis. A total of 3259 children (76.3%) did not develop a reaction to PPD, (0 mm), 170 (4%) had 1 to < 5 mm reading, 509 (11.9%) had 5 to 9 mm and 333 (7.8%) had >= 10 mm. Approximately 62% of the vaccinated children had received BCG vaccine in first year of life. Two hundred ninety (61.8%) of 469 children <= 5 were vaccinated and 179 (38.2%) were not. Only 22 of the youngest vaccinated had positive PPD. Twelve children were diagnosed with tuberculosis, a prevalence of 280 per 100,000. However, the prevalence of latent tuberculosis was 7.51%. Conclusion: Our prevalence of tuberculosis and latent tuberculosis is a sentinel indicator of continued transmission in the community. The data support the current recommendations that children who receive BCG can and should be tested with PPD for latent tuberculosis and tuberculosis.