Prevalence of tuberculous infection among school children in Kerala

There is paucity of information on epidemiological situation of Tuberculosis (TB) in the State of Kerala. The DOTS strategy under the Revised National Tuberculosis Control Programme (RNTCP) was introduced in the year 1998 to cover the entire State by 2002.

To estimate the prevalence of tuberculous infection among children attending 1-4th standard in a sample of selected schools in Kerala.

A cluster-sample school-based tuberculin survey was carried out in 70 schools selected by a two-stage sampling procedure. A total of 4821 children (including those with and without BCG scar) in the age group of 5-9 years were tuberculin tested using 1 TU PPD RT23 with Tween 80 and the maximum transverse diameter of induration was measured about 72 hours later. About 81% of the children were found to have BCG scars. Analysis was also undertaken by mixture model.

While 67% of children without BCG scar and 62% with scar did not elicit any induration at the test site, the mode or anti-mode of reactions due to infection with tubercle bacilli could not be identified from the distribution graphs. Analysis by mixture model also did not provide the best fit thus precluding estimation of prevalence of infection. About 5% of children had reactions > or =10 mm, 3% had reactions > or =12 mm and 2% had reactions > or =14 mm.

Low proportion of reactors indicated a low level of transmission of infection in Kerala. Considering the problems in interpretation of tuberculin survey data, it may not be feasible to use ARTI as an epidemiological parameter to monitor future trends of TB situation in the state.