Age patterns of severe paediatric malaria and their relationship to Plasmodium falciparum transmission intensity

Abstract

Background: The understanding of the epidemiology of severe malaria in African children remains incomplete across the spectrum of Plasmodium falciparum transmission intensities through which communities might expect to transition, as intervention coverage expands.

Methods: Paediatric admission data were assembled from 13 hospitals serving 17 communities between 1990 and 2007. Estimates of Plasmodium falciparum transmission intensity in these communities were assembled to be spatially and temporally congruent to the clinical admission data. The analysis focused on the relationships between community derived parasite prevalence and the age and clinical presentation of paediatric malaria in children aged 0-9 years admitted to hospital.

Results: As transmission intensity declined a greater proportion of malaria admissions were in older children. There was a strong linear relationship between increasing transmission intensity and the proportion of paediatric malaria admissions that were infants (R2 = 0.73, p < 0.001). Cerebral malaria was reported among 4% and severe malaria anaemia among 17% of all malaria admissions. At higher transmission intensity cerebral malaria was a less common presentation compared to lower transmission sites. There was no obvious relationship between the proportions of children with severe malaria anaemia and transmission intensity.

Conclusion: As the intensity of malaria transmission declines in Africa through the scaling up of insecticide-treated nets and other vector control measures a focus of disease prevention among very young children becomes less appropriate. The understanding of the relationship between parasite exposure and patterns of disease risk should be used to adapt malaria control strategies in different epidemiological settings.

Figure 1

Hospital sites included in the study of the age and clinical epidemiology of hospitalized paediatric malaria: Kilifi District Hospital (A), Althowra Hospital (B), Royal Victoria Hospital & the Medical Research Council hospital (C), Yemeni Swedish Hospital (D), Kilimanjaro CMC (E), Humera district Hospital (F), Kabale regional refferal Hospital (G), Mangochi district Hospital (H), Sibanor Clinic (I), Korogwe District Hospital (J), Siaya District Hospital (K), St Francis Hospital (L).

Figure 2

Age distribution of hospitalized malaria from 17 communities arranged by decreasing PfPR_2–10 (Plasmodium falciparum parasite prevalence in children 2 to 10 years). The bars denote the percentage of children in each single age group of all malaria admissions 0–9 years at each site.

Figure 3

Age specific proportion of total hospitalized paediatic malaria cases under different transmission intensities (x-axis; PfPR_2–10-Plasmodium falciparum parasite prevalence in children 2 to 10 years). The graphs show for each study sites the proportion of total malaria cases in children < 1 year (Figure 3a) and the proportion of total malaria cases in children 5–9 years (Figure 3b).

Figure 4

Proportion of total malarial cases diagnosed with clinical syndrome of cerebral malaria (Figure 4a) and severe malarial anaemia (Figure 4b) under different transmission intensities (PfPR_2–10 – Plasmodium falciparum parasite prevalence in children 2 to 10 years).