| Summary: | In 1956 a controlled trial of chemoprophylaxis against tuberculosis was launched in Greenland. Medication, either isoniazid (INH) or placebo, was given on a community basis, so that all inhabitants in one village received the same drug. The dosage of INH was low and intermittent, a total of 2200 mg over six months. In all, 76 villages were included in the study, and the medication was randomly allocated. Since the villages varied greatly in size they were grouped in clusters. Each of the 18 clusters represents a population of approximately 400 participants, all of whom were adult tuberculin reactors with no previous history of tuberculosis and no previous bacillus Calmette-Guérin (BCG) vaccination. The effectiveness of INH was evaluated by cluster analysis. The incidence of tuberculosis in the INH villages was compared with that in the placebo villages, computed as the average of the rates for the clusters. INH had an effect during the first six follow-up years, when the morbidity was one-third lower than in the placebo group. During the next six years no effect was evident. The effect of INH was independent of the initial x-ray findings. INH decreased the incidence of bacillary cases but had no demonstrable effect on the incidence of cavitary and fatal cases. All controlled studies have shown that INH had an effect, although the effect varied widely. However, a mass program poses problems from a public health point of view; the long lasting medication is a drawback, and side-effects, including fatalities, have been observed in numbers which cannot be disregarded. The main problem in a low prevalence country is partly an epidemiologic one (the inexpensive identification of small groups carrying a high rate and producing many cases) and partly an economic one (evaluation of the costs and benefits of a mass chemoprophylaxis program versus the present tuberculosis control system).
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