Risk factors for Plasmodium falciparum infection in the Kenyan Highlands: a cohort study.

Jackie Cook,Gillian Stresman,Elizabeth Marube,Jennifer C Stevenson,Amrish Baidjoe,Chrispin Owaga,Robin Migiro,Chris Drakeley,Jon Cox

doi:10.1093/trstmh/try122

Abstract

BackgroundMalaria transmission in African highland areas can be prone to epidemics, with minor fluctuations in temperature or altitude resulting in highly heterogeneous transmission. In the Kenyan Highlands, where malaria prevalence has been increasing, characterising malaria incidence and identifying risk factors for infection is complicated by asymptomatic infection.MethodsThis all-age cohort study, one element of the Malaria Transmission Consortium, involved monthly follow-up of 3155 residents of the Kisii and Rachuonyo South districts during June 2009–June 2010. Participants were tested for malaria using rapid diagnostic testing at every visit, regardless of symptoms.ResultsThe incidence of Plasmodium falciparum infection was 0.2 cases per person, although infections were clustered within individuals and over time, with the majority of infections detected in the last month of the cohort study. Overall, incidence was higher in the Rachuonyo district and infections were detected most frequently in 5–10-year-olds. The majority of infections were asymptomatic (58%). Travel away from the study area was a notable risk factor for infection.ConclusionsIdentifying risk factors for malaria infection can help to guide targeting of interventions to populations most likely to be exposed to malaria.

Highlights

Malaria in African highland areas is typically characterised as unstable or epidemic
Highland regions are classified as fringe areas of malaria transmission and are considered possible targets for elimination
The population residing in the western highlands in Kenya has been subject to malaria epidemics since the 1930s,9 despite traditional dogma dictating that the relatively high altitude should have been a barrier to malaria transmission

Summary

Introduction

Malaria in African highland areas is typically characterised as unstable or epidemic. Small changes in altitude and temperature, land use and population movement, can result in highly heterogeneous transmission.[1,2,3,4,5,6,7,8] Highland regions are classified as fringe areas of malaria transmission and are considered possible targets for elimination. Establishing risk factors for infection may help to target interventions to areas or populations where residual transmission remains. Malaria transmission in African highland areas can be prone to epidemics, with minor fluctuations in temperature or altitude resulting in highly heterogeneous transmission. In the Kenyan Highlands, where malaria prevalence has been increasing, characterising malaria incidence and identifying risk factors for infection is complicated by asymptomatic infection

Methods

Results

Conclusion