Distribution of tuberculous infection and disease among households in a rural community.

Clinical experience has led to a strong belief that tuberculosis is a family disease and contact examination is a sine qua non for case-finding programmes. Considerable doubts are cast on the usefulness of contact examination in tuberculosis control by the present study, which is based on a sample of an entire population rather than on family contacts of known cases only. Cases of tuberculosis occurred mostly singly in households, and contact examination could have revealed only a very small percentage of the cases in this community.Another common belief is that the prevalence of infection among children under five years of age is a good index of disease in households. In this study, however, a large proportion of households with cases of tuberculosis had no children of this age, and even in homes with a bacteriologically confirmed case, about 88% of the children did not show evidence of infection.The tuberculin reactions of infected contacts were, on the average, slightly larger than those among non-contacts. Further, the proportion of large tuberculin reactions among infected persons was found to be greater in the younger age-groups than in the older age-groups. This finding has been taken to indicate that new infection gives rise to large reactions that subsequently wane to some extent in persons not constantly exposed to infection, such as, for example, the members of households without cases.