Trend in tuberculosis infection prevalence in a rural area in South India after implementation of the DOTS strategy

Abstract

Three tuberculin surveys were conducted at intervals of 5 years following the implementation of a DOTS-based programme in 1999 in Tiruvallur District, South India. To estimate the trend in the prevalence of tuberculosis (TB) infection among children and to evaluate the impact of the DOTS strategy. Children aged 1-9 years in the sample for each survey were registered and administered 1 tuberculin unit of purified protein derivative RT 23 with Tween 80 by intradermal injection on the volar aspect of the left forearm. The induration diameter of the reaction was measured in mm after 72 h (3 days) and the prevalence of TB infection estimated. The induration data of bacille Calmette-Guérin (BCG) vaccinated and non-vaccinated children were analysed using the mixture model. The estimated prevalence of TB infection among non-BCG-vaccinated children in the three tuberculin surveys were respectively 19.4%, 13.8% and 11.4%, with an average annual decline of 5.2% (95%CI 3.6-6.8). The prevalence of TB infection among BCG-vaccinated children decreased, with an average annual decline of 5.4% (95%CI 10.0-18.6). A significant declining trend in the prevalence of TB infection among children was observed following the implementation of the DOTS strategy in the area.