THE ANNUAL RISK OF INFECTION WITH MYCOBACTERIUM-TUBERCULOSIS IN ENGLAND AND WALES SINCE 1901

SETTING: England and Wales. OBJECTIVE: To estimate the magnitude and t rend in the annual risk of infection with Mycobacterium tuberculosis i n England and Wales since 1901. DESIGN: Estimates for the prechemother apy era are derived assuming that 1% of new infections among 0-4 year olds led to fatal tuberculosis meningitis, as found in the Netherlands . The estimates are validated against data from the 1949-1950 national tuberculin survey. We explore the trend thereafter using tuberculous meningitis notifications and data from the 1971-1973 national tubercul in survey, and discuss the utility of data collected under the nationa l bacille Calmette-Guerin (BCG) vaccination scheme for estimating the annual risk of infection. RESULTS: Tuberculosis meningitis mortality r ates among 0-4 year olds declined at 4% per annum until 1950, and sugg est that the annual risk of infection declined from 12% in 1901 to 1.9 % in 1949. The decline in the annual risk of infection probably accele rated in 1950, although its magnitude cannot be determined accurately. CONCLUSION: An accelerated decline in the annual risk of infection in England and Wales from 1950 probably resulted from the introduction o f chemotherapy, which dramatically reduced the prevalence of sources o f infection in the population. Data collected during the national BCG vaccination scheme were found to be unsuitable for estimating infectio n risks.