No single patient with multiple sclerosis (M.S.) has yet been found among South Africa's 11 million Bantu. The disease does occur among the Coloured and Asian South Africans, but it is very uncommon. A survey of its annual incidence, prevalence, and annual mortality among the 3 million White population of South Africa is reported. For all White South Africans the average annual incidence was 0.6 per 100,000. There were 281 White patients with probable M.S. on prevalence day 1960, giving an overall prevalence rate of 9.1 or 11.0 per 100,000 when agecorrected to the population of England and Wales. The annual average mortality in recent years was 0.4 per 100,000. The female: male sex ratio was higher than has been found in other studies among immigrants from the continent of Europe and among the White English-speaking South-African-born. The annual incidence, prevalence, and mortality are low for the Afrikaans-speaking White South-African-born, between three and four times higher for the English-speaking White South-African-born, and between 10 and 11 times higher for White immigrants from Central and Northern Europe, including the United Kingdom. These European immigrants had apparently the same risk of developing M.S. as in their country of birth. Immigrants from Southern Europe and White immigrants born elsewhere, usually in other African countries, had a low prevalence of M.S. There was no significant difference in prevalence for the different groups of White South Africans between the cities, other urban areas and rural areas, nor between the four provinces of South Africa. M.S. occurred more often in two members of a family than would be expected by chance, but it is not clear whether this is because certain families are genetically predisposed to the disease or because members of a family share the same environment. The steep gradient in the prevalence of M.S. among people of the same European genetic stock in South Africa is evidence that an environmental factor is mainly responsible for M.S. Emigration from a high-risk area to South Africa, a low-risk area, does not apparently lessen the risk of developing the disease. From the present evidence I believe that the gradient of prevalence of M.S. in South Africa, taken in conjunction with the findings of other prevalence surveys elsewhere in the world, strongly suggests that the condition is normally an infection of infancy, probably a virus infection, and that those who are exposed to such living conditions in childhood that they miss early infection may develop multiple sclerosis later in life. © 1967, British Medical Journal Publishing Group. All rights reserved.
