Meteorologic influences on Plasmodium falciparum malaria in the Highland Tea Estates of Kericho, Western Kenya

Abstract

Recent epidemics of Plasmodium falciparum malaria have been observed in high-altitude areas of East Africa. Increased malaria incidence in these areas of unstable malaria transmission has been attributed to a variety of changes including global warming. To determine whether the reemergence of malaria in western Kenya could be attributed to changes in meteorologic conditions, we tested for trends in a continuous 30-year monthly malaria incidence dataset (1966-1995) obtained from complete hospital registers at a Kenyan tea plantation. Contemporary monthly meteorologic data (1966-1995) that originated from the tea estate meteorologic station and from global climatology records were also tested for trends. We found that total hospital admissions (malaria and nonmalaria) remained unchanged while malaria admissions increased significantly during the period. We also found that all meteorologic variables showed no trends for significance, even when combined into a monthly suitability index for malaria transmission. We conclude that climate changes have not caused the highland malaria resurgence in western Kenya.

Figure 1

Malaria, hospital admissions, and meteorologic station data, Kericho tea estate, 1966–1995. Malaria incidence (a) total hospital admissions (b) mean monthly temperature (c) and total monthly rainfall (d) are all plotted with a 25-point (month) moving average (bold) to show the overall movement in the data. The significance of these movements is presented in Table.

Figure 2

Climate and malaria suitability data for the Kericho area from the global gridded climatology data, including meteorologic and malaria suitability time series. Minimum (bottom), mean (middle) and maximum (top) monthly temperature (a) total monthly precipitation (b) and mean vapor pressure (c) are all plotted with a 25-point (month) moving average (bold) to show the overall movement in the data. The number of months per year suitable for malaria transmission (d) are also plotted. Suitability was determined if rainfall exceeded 152 mm and temperature exceeded 15°C in any month (1,4). The significance of these movements is presented in Table.