The annual risk of infection with Mycobacterium tuberculosis in England and Wales since 1901

SETTING: England and Wales. OBJECTIVE: To estimate the magnitude and trend in the annual risk of infection with Mycobacterium tuberculosis in England and Wales since 1901. DESIGN: Estimates for the prechemotherapy 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 tuberculin survey, and discuss the utility of data collected under the national bacille Calmette-Guerin (BCG) vaccination scheme for estimating the annual risk of infection. RESULTS: Tuberculosis meningitis mortality rates among 0-4 year olds declined at 4% per annum until 1950, and suggest 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 accelerated 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 of chemotherapy, which dramatically reduced the prevalence of sources of infection in the population. Data collected during the national BCG vaccination scheme were found to be unsuitable for estimating infection risks.