Prevalence study of tuberculous infection over fifteen years, in a rural population in Chingleput district (south India).

As in the earlier BCG trial against tuberculosis conducted in Chingleput district in south India (in 1969), the entire study population was tuberculin tested (Survey I), a study was undertaken subsequently to see whether in this population there was any change in the tuberculosis situation in terms of prevalence of infection in children. For this purpose, in two of the panchayat unions, in a random sample of panchayats, tuberculin testing was repeated twice at an interval of 10 yr (Survey II) and 15 yr (Survey III) after the initial testing in children aged 1-9 yr. High coverages were obtained for tuberculin testing and reading. Data from 8,703 and 9,709 children at Surveys I and II respectively was used for comparing the prevalence of infection over a period of 10 yr and from 4,808, 4,965 and 4,889 children at Surveys I, II and III respectively for comparing the prevalence of infection over a period of 15 yr. The results showed that although the prevalence of infection varied in the two panchayat unions, within each panchayat union it did not differ significantly at the three surveys. The overall prevalence of infection at the three surveys was 9.0, 10.2 and 9.1 per cent respectively. The average annual risk of tuberculous infection was estimated to be 1.7, 1.9 and 1.7 per cent at the three surveys respectively. Thus, the results clearly showed that, over a period of 15 yr, there was no change in the tuberculosis situation, in terms of prevalence of infection, in the study population.

Post-vaccination tuberculin sensitivity for assessing BCG vaccination in areas with high prevalence of non-specific sensitivity.

The relationship of non-specific sensitivity to post-vaccination tuberculin sensitivity has been the subject of controversy. This relationship has an important bearing on the common practice of using post-vaccination tuberculin sensitivity for assessing BCG vaccination in areas with a high prevalence of non-specific sensitivity. If post-vaccination tuberculin sensitivity is found to be dependent on the amount of already existing, naturally acquired, non-specific sensitivity it could not be considered a reliable measure of the success of BCG vaccination. In a recent BCG trial in India a large number of persons were tested with PPD-S and PPD-B and also vaccinated with BCG vaccine or injected with placebo, by random allocation. Mutually exclusive random samples of the study population were retested with PPD-S at 2 1/2 months, 2 1/2 years and 4 years after vaccination. At each post-vaccination test the tuberculin sensitivity obtained among the placebo-injected controls provided a measure of the tuberculin sensitivity due to non-specific sensitivity that would have been present in the absence of BCG vaccination. The difference between the mean size of reactions to the post-vaccination test among the vaccinated and among the unvaccinated controls provided a measure of tuberculin sensitivity that was wholly due to BCG vaccination. Thus it was possible to separate and study the two components of post-vaccination tuberculin sensitivity. The results of the study indicate that post-vaccination tuberculin sensitivity can be used to assess BCG vaccination in areas with a high prevalence of non-specific sensitivity, provided the assessment is done in younger age groups and based on post-vaccination tuberculin sensitivity as measured at 2-3 months after vaccination and not later.

Feasibility of a chemoprophylaxis trial in India against tuberculosis. A pilot study.

A pilot study in Bangalore to investigate the feasibility of a chemoprophylaxis trial with isoniazid is described.For a chemoprophylaxis trial, 2 basic requirements are that a large number of participants must take the drug and that reliable estimates of the amount of drug consumed should be available. Distribution of weekly supplies of pills for self-medication was tried and actual consumption was checked by urine examination using the Belles-Littleman filter-paper spot test. Except during the first month, the proportion of positive urine samples was very small.Estimating drug consumption by "pill counting" or by means of house-to-house interview was not reliable. These methods are not recommended for a chemoprophylaxis trial in India.Direct administration of pills to each participant every day for 6 months by a locally employed person resulted in a much higher consumption of pills. In spite of some deliberate false recording and some genuine recording errors, the results are considered encouraging enough to warrant further trials. Procedures are simpler and records of consumption for each individual are available. The method also provides the opportunity to use the individual, and not the family, as the unit for randomization between treatments.The proportion of positive urine samples provides an objective means of assessing the reliability of estimates of drug intake by other methods but large numbers of urine samples would be required if this method were to be used independently for estimating individual pill consumption.

Influence of isoniazid on naturally acquired tuberculin allergy and on induction of allergy by BCG vaccination.

Previous studies on the influence of isoniazid on the size of the tuberculin reaction have given conflicting results. A controlled study in an area with high prevalence of low-grade allergy has been carried out by the administration of isoniazid or placebo tablets. For those not vaccinated with BCG, isoniazid in a single daily dose of 5 mg/kg body-weight tended to reduce somewhat the size of the tuberculin reaction among those with reactions of 12 mm or more at the initial tuberculin test.In people who were vaccinated with BCG, isoniazid given simultaneously resulted in significantly less increase in the size of post-vaccination tuberculin reactions as compared with controls; the difference was still significant, in tests conducted 4(1/2) months after the discontinuation of isoniazid. However, in spite of isoniazid, the post-vaccination allergy induced by BCG was quite considerable. This considerable increase in post-vaccination allergy suggests that the vaccination was successful in spite of the administration of isoniazid and makes it clear that primary chemoprophylaxis could be combined with BCG vaccination.Administration of isoniazid for 2 months is estimated to have killed about 90% of the bacilli in the BCG vaccine injected intracutaneously.