The prevalence and annual rate of tuberculous infection in South Africa

The prevalence and incidence rates of tuberculous infection were calculated from 170 000 Mantoux test results gathered by the Tuberculosis Research Institute between 1974 and 1980 and also from tuberculin survey results from other sources covering the periods 1944-45 and 1953-54. Prevalence rates in 10-year-olds were generally low in the Asian and White groups, less than 5 % at present, and fairly high in the Coloured and Black groups, whose rates ranged from 10 % to 20 %. Very little difference was found between the prevalence rates of the urban and rural populations in any of the age groups surveyed, but as a rule higher rates were found in lowland (mostly coastal) than in highland regions. An overall annual decrease over the past 25–30 years of 5 % in the infection rates of Blacks and Coloureds was estimated, and of 7 % and 8 % in Asians and Whites. However, it is suggested that these downward trends have increased progressively in all ethnic groups in South Africa in recentyears, but that annually they do not exceed 13%. Annual rates of infection in 7-year-olds were expected to reach 1–2 per 1000 Blacks by 1982. One tuberculous infection annually per 1000 population may be considered sufficiently low for the disease to be regarded as of minimal importance. In South African Whites this level has already been reached and it is expected to be in Asians within the next 5–10 years. In Coloureds and Blacks another 20 to 30 years will have to pass before this level is reached. Les taux de prévalence et d'incidence de ('infection tuberculeuse ont été' calculés à partir des résultats de 170 000 tests de Mantoux recueillis au Tuberculosis Research Institute entre 1974 et 1980, ainsi qu'à partir des résultats d'enqut̂es tuberculiniques d'autres sources couvrant les périodes 1944–1945 et 1953–1954. Les taux de prévalence chez les sujets de 10 ans étaient généralement fiables dans les groupes de sujets asiatiques et blancs (il est actuellement inférieur à 5 %) et assez élevé dans les groupes desujets de couleur et noirs, parmi lesquels ils s'échelonnaient de 10 à 20 %. On a trouvé peu de différence entre les taux de prévalence des populations urbaine et rurale quelque soit le groupe téste et, d'une manière générale, les taux ont été trouvés plus bas dans les terres basses (essentiellement cotières) que clans les regions de hautes terres. On a estimé que clans ('ensemble le pourcentage annuel de diminution du taux d'infection au cours des 25 à 30 derniéres années a