Background and objective: The tuberculin test is widely used for the diagnosis of tuberculosis (TB) in children, as it is the only one to provide evidence of infection with Mycobacterium tuberculosis. Our objective was to estimate the prevalence of TB infection, the annual risk of infection (ARI), and the incidence of active TB in school children.
Methods: A cross-sectional study was carried out in Ahvaz, a city of southern Iran, in 2006. A questionnaire was used to collect information, including demographic characteristics, bacillus Calmette-Guérin (BCG) vaccination history, and household contact with active TB. Tuberculin testing was performed. Reactivity that measured < 5 mm was considered negative, between 5 and 9 mm was considered doubtful, and > or = 10mm was considered positive. Chest radiographs were obtained as part of the evaluation for children with a positive result.
Results: A total of 3906 children with a mean+/-standard deviation (SD) age of 10.59+/-2.63 years (51% female, 49% male) were entered into our study. Of these, 3338 children (85.5%) did not develop a reaction (0mm), 243 (6.2%) had reactivity of 1-4mm, 238 (6.1%) had reactivity of 5-9 mm, and 87 (2.2%) had reactivity of > or = 10 mm. More than 90% of the children had received the BCG vaccine in the first week of life. The ARI rate was 0.5% and the estimated case of smear-positive TB was approximately 25 per 100000 population. Only three children were diagnosed with active TB, a prevalence of 75 per 100000 population.
Conclusions: Tuberculin testing using 5TU-PPD (5 tuberculin units of purified protein derivative) is a valuable diagnostic test for latent TB and active TB in childhood. BCG vaccination has no remarkable effect on the interpretation of tuberculin reactivity. The incidence rate of active pulmonary TB in children in the region of study is of concern.