Yes, it is a hidden disease. The patient remains asymptomatic for long periods, and the disease is often diagnosed during routine tests, when a chest X-ray reveals the 'hidden' disease, i.e. tuberculosis. It has thus an occult/hidden character.

In places where the incidence of tuberculosis is not marked, 'tuberculin test surveys' be carried out among the general population, which gives an idea of the number of cases who are tuberculin positive, i.e. infected with tubercle bacilli (although the disease may be inactive in the majority of them). Those who have shown positive in the tuberculin test should be subjected to an X-ray examination of the chest, so as to find out hidden/ symptomless, especially active cases of the disease - in other words those who are suffering from active tuberculosis, but still showing no symptoms of the disease, can be detected.

For an epidemiological survey, small X-rays may be taken through a special X-;ray plant fitted in a van, which moves from place to place or village to village, or visits poor communities/slums. X-rays are taken in quick succession, one by one, of the various persons, who 'are made to stand in a queue before entering the van. They come out of the van after the exposure for the chest X-ray. This is called miniature mass radiography (MMR). These surveys were most common in the past when the disease was at its peak.

However, in places where the incidence of tuberculosis is high, all persons in such areas are expected to be infected with tubercle bacilli, i.e. they will be found as tuberculin positive. Hence the tuberculin test is of little value at such places, for epidemiological survey, and therefore, one can directly switch on to MMR study, for the detection of both hidden and active cases of tuberculosis.