Risk factors associated with the acquisition of sleeping sickness in north-east Zambia; a case-control study.

A case-control study identified 59 cases of Rhodesian sleeping sickness in the northern Luangwa valley of Zambia together with age- and sex-matched nearest neighbour and hospital controls. Birth outside the trypanosomiasis endemic area was not shown to increase the risk of acquiring sleeping sickness. Significantly more cases under the age of 20 years had lived outside the endemic area compared with neighbour controls, although this was not true for those over 20 years old. Ethnic group and main occupation did not differ between cases and neighbour controls. Fishing as an auxiliary occupation increased the risk infection. Members of the United Church of Zambia had a relative risk of acquiring trypanosomiasis twice as great as other religious groups, perhaps because their scattered churches involve more walking through tsetse-infected bush. Sleeping sickness cases said that there were zebras near their village significantly more often than controls, although zebras are not usually considered a likely source of infection. In a preliminary study there was no difference in blood groups or haemoglobin genotype between cases and controls.