The decline in paediatric malaria admissions on the coast of Kenya

Abstract

Background: There is only limited information on the health impact of expanded coverage of malaria control and preventative strategies in Africa.

Methods: Paediatric admission data were assembled over 8.25 years from three District Hospitals; Kilifi, Msambweni and Malindi, situated along the Kenyan Coast. Trends in monthly malaria admissions between January 1999 and March 2007 were analysed using several time-series models that adjusted for monthly non-malaria admission rates and the seasonality and trends in rainfall.

Results: Since January 1999 paediatric malaria admissions have significantly declined at all hospitals. This trend was observed against a background of rising or constant non-malaria admissions and unaffected by long-term rainfall throughout the surveillance period. By March 2007 the estimated proportional decline in malaria cases was 63% in Kilifi, 53% in Kwale and 28% in Malindi. Time-series models strongly suggest that the observed decline in malaria admissions was a result of malaria-specific control efforts in the hospital catchment areas.

Conclusion: This study provides evidence of a changing disease burden on the Kenyan coast and that the most parsimonious explanation is an expansion in the coverage of interventions such as the use of insecticide-treated nets and the availability of anti-malarial medicines. While specific attribution to intervention coverage cannot be computed what is clear is that this area of Kenya is experiencing a malaria epidemiological transition.

Figure 1

Map showing the three study districts and the location of the metrological station in relation to the hospital facility. Inset is a map of Kenya showing location of three districts.

Figure 2

Admissions by month for the period January 1999 to March 2007 at three sites on the Kenyan coast. The top row is Kilifi, the middle row Kwale and the bottom Malindi. The graphs show malaria admissions (left column) and non-malaria admissions (right column) as dashed lines. The yellow solid line is a 13-point moving average applied to filter seasonal variation and highlight the long-term movements in the data. The two solid tone lines illustrate the change in admissions adjusted for seasonality (light grey) and seasonality, rainfall and non-malaria admissions (black). The intercept was chosen (from the potential 11) based on the maximal correlation with the 13-point m.a.

Figure 3

Rainfall per month for the period January 1999 to March 2007 at three sites on the Kenyan coast. The top row is Kilifi, the middle row Kwale and the bottom Malindi. The graphs in the left column show the monthly rainfall in mm as dashed lines. The yellow solid line is a 13-point moving average applied to filter seasonal variation and highlight the long-term movements in the data. Trends corrected for seasonality are shown in black. The rainfall expressed as anomalies relative to 1999–2007 monthly mean for each site are shown in the middle column. The 13-point moving average is again also shown. The intercept was chosen (from the potential 11) based on the maximal correlation with the 13-point m.a.

Figure 4

Cumulative monthly ITN distribution volumes expressed per capita across the three districts of Malindi, Kilifi and Kwale.