Epidemiological basis of tuberculosis eradication. 10. Longitudinal studies on the risk of tuberculosis in the general population of a low-prevalence area.

The introduction of chemotherapy dramatically changed the epidemiology of tuberculosis as the risk of infection was thereby nearly eliminated. The present paper illustrates the risk of disease under these conditions. A large and representative segment of the Danish population, a total of over 626 000 persons aged 15-44 years, was examined by a standardized technique in 1950-52 and has now been followed for 12 years. It has been possible by means of simple parameters such as infection and vaccination status, X-ray lesion and age to divide the population into groups with widely different incidence rates. The time trend in disease rates among vaccinated persons and natural reactors suggests that post-primary tuberculosis is of great significance in the present tuberculosis situation. Three-quarters of all cases stem from the natural reactors. It would have been of great practical significance to identify high-risk groups which yielded a great part of the patients. This was not possible since the majority of cases developed among reactors whose distinctive feature was that they were infected at time of examination.