Risk factors for malaria among British missionaries living in tropical countries.
Thirty-two episodes of malaria (10 confirmed by laboratory tests) were reported by 162 people living in 18 developing countries under the auspices of one British missionary society. Malaria was endemic in all countries involved, and a total of 367 person-years were observed. The overall incidence rate for malaria was 87.3 per 1000 person-years at risk. Important factors identified were residence in West Africa compared with elsewhere (relative risk (RR) = 13.0, P less than 0.001), being in the 20-39 year age group (RR = 3.2, P less than 0.002), history of gastroenteritis (RR = 3.1, P less than 0.002) and living in a rural area (RR = 1.7, n.s.). Chemoprophylaxis was taken by 119 people (73.5%).