Travel as a Risk Factor for Malaria Requiring Hospitalization on a Highland Tea Plantation in Western Kenya

BACKGROUND: Over the past two decades, endemic malaria returned to the western highlands of Kenya, a region that had been free of endemic malaria during the preceding 30 years. A study of malaria patients admitted to a tea estate hospital was conducted to estimate the risk of severe malaria when acquired during travel away from the tea estates compared with infections that had probably been locally acquired. METHODS: From May 1998 to March 2000, 1,296 patients were evaluated with a case-control design and standardized questionnaire during their hospitalization. Death certificates from the tea estates were examined from 1964 to 1972 and 1986 to 1999. RESULTS: Travel away from the tea estates during the 2 months prior to hospitalization (n = 432) was strongly associated with a diagnosis of malaria (odds ratio 2.7, 95% CI 2.1-3.5). The estimate of risk associated with travel was consistent with known malaria endemicity, the Rift Valley Province having a much lower malaria transmission than the area around Lake Victoria. The seasonality of malaria-related deaths indicates that many lowland-origin children probably contracted their fatal infection away from the tea plantation. CONCLUSIONS: Travel within Kenya is a significant risk factor for hospitalization owing to malaria on the tea estates; expatriate travelers need to be aware that the East African highlands cannot be regarded as malaria free.