Geographical variations in the prevalence of chest x-ray abnormalities detected in tuberculosis surveys in eight African countries south of the Sahara.

A number of national tuberculosis surveys were carried out in the African Region by WHO teams from 1955 to 1960. Chest X-ray examinations were included in most of these surveys, but comparison of the results from different countries was not possible on the basis of the original readings as different X-ray interpreters had been used in the different surveys.A further study was therefore conducted in which the survey films were re-read by a single reader, so as to eliminate inter-reader variation and thereby obtain comparable estimates of the prevalence of tuberculosis as well as of cardiac enlargement and dilatation of the aorta.A method of analysis of variance was used to compare variations from group to group and from country to country, as well as between larger areas within the African continent.It was found that the prevalence of radiologically established tuberculosis was significantly higher in East than in West Africa, and that dilatation of the aorta was up to five times more prevalent along the West African coast than in the Highlands of East Africa. The country-to-country variation did not exceed that expected by chance, and the study seems to underline the fact that epidemiological variations in Africa do not follow national frontiers, but that they are associated with ecological variables which differ between broad regions within the continent.