Trends in the annual risk of tuberculous infection in India.

SETTING: Twenty-four districts in India. OBJECTIVES: To evaluate trends in annual risk of tuberculous infection (ARTI) in each of four geographically defined zones in the country. STUDY DESIGN: Two rounds of house-based tuberculin surveys were conducted 8-9 years apart among children aged 1-9 years in statistically selected clusters during 2000-2003 and 2009-2010 (Surveys I and II). Altogether, 184,992 children were tested with 1 tuberculin unit (TU) of purified protein derivative (PPD) RT23 with Tween 80 in Survey I and 69,496 children with 2TU dose of PPD in Survey II. The maximum transverse diameter of induration was measured about 72 h after test administration. ARTI was computed from the prevalence of infection estimated using the mirror-image method. RESULTS: Estimated ARTI rates in different zones varied between 1.1% and 1.9% in Survey I and 0.6% and 1.2% in Survey II. The ARTI declined by respectively 6.1% and 11.7% per year in the north and west zones; no decline was observed in the south and east zones. National level estimates were respectively 1.5% and 1.0%, with a decline of 4.5% per year in the intervening period. CONCLUSION: Although a decline in ARTI was observed in two of the four zones and at national level, the current ARTI of about 1% in three zones suggests that further intensification of TB control activities is required.

The annual risk of tuberculous infection in Orissa State, India.

SETTING: Rural and urban areas of eight selected districts of Orissa State, India. OBJECTIVES: To estimate the average annual risk of tuberculous infection (ARTI) in the state. DESIGN: A community-based, cross-sectional tuberculin survey was conducted among children aged 1-9 years residing in a sample of rural and urban areas of eight districts of Orissa State. A stratified sampling was adopted for selection of clusters. Highly trained designated tuberculin testers administered 0.1 ml (1 TU) of PPD RT 23 with Tween 80 by the Mantoux method to 10 626 children. Transverse tuberculin reaction sizes were measured about 72 h later by trained designated tuberculin readers. The number of children satisfactorily test-read was 10 191. RESULTS: Based on the frequency distribution of tuberculin reaction sizes, the average ARTI in the state was estimated at 1.7-1.8%. The children residing in urban areas were observed to be at a significantly higher risk of infection than those in rural areas. CONCLUSION: The study in Orissa State suggests high rates of transmission of tuberculous infection and calls to attention the need for intensification of concerted and sustained tuberculosis control efforts.

Prevalence of tuberculosis in a rural area by an alternative survey method without prior radiographic screening of the population.

SETTING: Mass miniature radiography (MMR) is the usual tool for population screening in tuberculosis case prevalence surveys. However, this facility is not available at most centres in India. OBJECTIVE: The feasibility of conducting a survey without MMR screening was therefore investigated. DESIGN: The study was carried out in Bangalore rural district during 1984-1986. The area was the same as for six earlier prevalence surveys conducted since 1961. The population aged up to 44 years was tuberculin tested. Persons with test induration size of > or = 10 mm were eligible for sputum examination, besides all those aged over 45 years who were eligible without discrimination. RESULTS: Reduction of workload was not adequately achieved through screening, as 78.4% of the registered population (29,400) was still eligible for sputum examination. The changed screening procedure in this survey also made comparison with earlier data difficult. In spite of more liberal and comprehensive screening, the observed prevalence rate of cases (438/100,000 population aged 10+ years) was similar to earlier surveys. The prevalence rate of smear-positive cases, however, was much lower (68/100,000 population aged 10+ years). CONCLUSION: In conclusion, the candidate screening procedure was not suitable. The findings nevertheless conformed to the overall declining trend for the area, as reported earlier.

Tuberculous infection in a rural population of south India: 23-year trend.

A survey was conducted in Bangalore district of south India between February 1984 and January 1986 to study the tuberculosis infection rate. The data from this survey, along with the information derived from the earlier ones in the same area conducted between 1961-1968, have been used in the report to study the trend of tuberculosis. Tuberculin test results in 0- to 14-year-old unvaccinated children from each survey were distributed, and based on the antimode, infected persons were identified. The standardized prevalence rates in population from the surveys were converted into risk rates by using the TSRU methodology and compared. The average annual risk of infection of 1.1% observed in 1961 declined to 0.61% in 1985, representing a decline of approximately 37% in nearly 23 years. This amounted to an average decline of 3.2% per annum over the period. The trend probably represented a natural dynamics. Whether organized intervention played some role could not be commented upon. Similar studies in other parts of the country are recommended in order to have information on the trend in the country as a whole.

Tuberculin sensitivity and skin lesions in children after vaccination with 11 different BCG strains.

In previously published studies, a number of BCG strains used in several production laboratories were compared in animal models. Liquid vaccines from the different strains were prepared in one laboratory with a uniform technique, the aim being to obtain uniform in vitro properties. In the studies reported here, such vaccines were compared by means of vaccinating children in India and Denmark and then measuring their post-vaccination skin lesions and tuberculin sensitivity. One strain induced delayed hypersensitivity strikingly weaker than that induced by any of the others, although the vaccine was in no way inferior in terms of exhaustive in vitro tests. Differences among the other strains were slight, although sometimes statistically significant. The implications of such differences are discussed.