Malaria infection, disease and mortality among children and adults on the coast of Kenya

Abstract

Background: Malaria transmission has recently fallen in many parts of Africa, but systematic descriptions of infection and disease across all age groups are rare. Here, an epidemiological investigation of parasite prevalence, the incidence of fevers associated with infection, severe hospitalized disease and mortality among children older than 6 months and adults on the Kenyan coast is presented.

Methods: A prospective fever surveillance was undertaken at 6 out-patients (OPD) health-facilities between March 2018 and February 2019. Four community-based, cross sectional surveys of fever history and infection prevalence were completed among randomly selected homestead members from the same communities. Paediatric and adult malaria at Kilifi county hospital was obtained for the 12 months period. Rapid Diagnostic Tests (CareStart™ RDT) to detect HRP2-specific to Plasmodium falciparum was used in the community and the OPD, and microscopy in the hospital. Crude and age-specific incidence rates were computed using Poisson regression.

Results: Parasite prevalence gradually increased from childhood, reaching 12% by 9 years of age then declining through adolescence into adulthood. The incidence rate of RDT positivity in the OPD followed a similar trend to that of infection prevalence in the community. The incidence of hospitalized malaria from the same community was concentrated among children aged 6 months to 4 years (i.e. 64% and 70% of all hospitalized and severe malaria during the 12 months of surveillance, respectively). Only 3.7% (12/316) of deaths were directly attributable to malaria. Malaria mortality was highest among children aged 6 months-4 years at 0.57 per 1000 person-years (95% CI 0.2, 1.2). Severe malaria and death from malaria was negligible above 15 years of age.

Conclusion: Under conditions of low transmission intensity, immunity to disease and the fatal consequences of infection appear to continue to be acquired in childhood and faster than anti-parasitic immunity. There was no evidence of an emerging significant burden of severe malaria or malaria mortality among adults. This is contrary to current modelled approaches to disease burden estimation in Africa and has important implications for the targeting of infection prevention strategies based on chemoprevention or vector control.

Keywords: Adults; Age-pattern; Immunity; Infection; Malaria; Mortality; Severe disease.

Fig. 1

Map showing the study sites. This includes location of 29 geo-coded health facilities south of KHDSS including Kilifi county hospital (KCH) overlaid on the geocoded homesteads, location of the sisal plantation, farmlands or shrubs and the roads. Health facility where patients were enrolled are shown by the red crosses, blue cross are other health facilities in the area; enumeration zones are the cream polygons; road class means: B, National Trunk Road; C, Primary Roads; D, Secondary Roads

Fig. 2

Comparison of malaria metrics across all age in the study area. a Parasite prevalence (green line) and community fever test positive prevalence (purple line). b The health facility RDT period prevalence (red line) and health facility RDT incidence rate (blue line). c The incidence of uncomplicated malaria admission (gray bar) and incidence of severe malaria (black bars). d Incidence of deaths attributable to malaria

Fig. 3

Parasite prevalence between 1999 and 2001 (green line) [24, 48] and current parasite prevalence between 2018 and 2019 (red line)