However, as a mass screening program for low-risk populations, the procedure was largely discontinued in the 1970s, following recommendation of the World Health Organization, due to three main reasons:# The dramatic decrease of the general incidence of tuberculosis in developed countries (from 150 cases per 100,000 inhabitants in 1900, 70/100,000 in 1940 and 5/100,000 in 1950);# Decreased benefits/cost ratio (a recent Canadian study has shown a cost of CD$ 236,496 per case in groups of immigrants with a low risk for tuberculosis, versus CD$ 3,943 per case in high risk groups);# Risk of exposure to ionizing radiation doses, particularly among children, in the presence of extremely low yield rates of detection.