Contact examination is not recommended as a routine procedure for Case-finding in the District Tuberculosis Programme. The rationale for not including contact examination as a routine Case-finding measure is: (1) prevalence rate of tuberculosis among the contacts is not much higher than in the general population (2) at the time of diagnosis of an index case, a second case may not be found in the same household. Though more prevalence cases cannot be diagnosed by contact examination, is it possible that by keeping the household contacts, as a group, under surveillance, future incidence of cases in the community can be substantially prevented? A model situation has been created by using hypothesis derived from various studies conducted in India, designed to answer the question. Variables used in the model are: 40% of the general population are infected at any point of time, there is only one prevalence case of TB at any given point of time in an average household of five, 40% of the non-infected population in a contact household are infected per year, incidence of disease among newly infected group is seven, times of the incidence among previously infected, incidence of disease in general population is 0.13% and from among previously infected persons 0.3% per year develop sputum disease.

At an incidence rate of 0.13% per year among general population aged >5 years, it is expected that 111 cases would arise in a year in the population of 1,00,000 under study. Thus, of the 111 cases occurring in the community, 101 arise from those who are not contacts.

The proportional contribution of new cases from the contact group to the total incidence cases in the entire community is so small, that even if all the contacts are kept under surveillance, BCG vaccinated or placed on chemoprophylaxis, still over 90% of incidence cases cannot be prevented from occurring. This is apart from the fact that keeping them under surveillance will be highly costly and is an operational problem of considerable magnitude.