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      Spatially variable risk factors for malaria in a geographically heterogeneous landscape, western Kenya: an explorative study

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          Abstract

          Background

          Large reductions in malaria transmission and mortality have been achieved over the last decade, and this has mainly been attributed to the scale-up of long-lasting insecticidal bed nets and indoor residual spraying with insecticides. Despite these gains considerable residual, spatially heterogeneous, transmission remains. To reduce transmission in these foci, researchers need to consider the local demographical, environmental and social context, and design an appropriate set of interventions. Exploring spatially variable risk factors for malaria can give insight into which human and environmental characteristics play important roles in sustaining malaria transmission.

          Methods

          On Rusinga Island, western Kenya, malaria infection was tested by rapid diagnostic tests during two cross-sectional surveys conducted 3 months apart in 3632 individuals from 790 households. For all households demographic data were collected by means of questionnaires. Environmental variables were derived using Quickbird satellite images. Analyses were performed on 81 project clusters constructed by a traveling salesman algorithm, each containing 50–51 households. A standard linear regression model was fitted containing multiple variables to determine how much of the spatial variation in malaria prevalence could be explained by the demographic and environmental data. Subsequently, a geographically-weighted regression (GWR) was performed assuming non-stationarity of risk factors. Special attention was taken to investigate the effect of residual spatial autocorrelation and local multicollinearity.

          Results

          Combining the data from both surveys, overall malaria prevalence was 24 %. Scan statistics revealed two clusters which had significantly elevated numbers of malaria cases compared to the background prevalence across the rest of the study area. A multivariable linear model including environmental and household factors revealed that higher socioeconomic status, outdoor occupation and population density were associated with increased malaria risk. The local GWR model improved the model fit considerably and the relationship of malaria with risk factors was found to vary spatially over the island; in different areas of the island socio-economic status, outdoor occupation and population density were found to be positively or negatively associated with malaria prevalence.

          Discussion

          Identification of risk factors for malaria that vary geographically can provide insight into the local epidemiology of malaria. Examining spatially variable relationships can be a helpful tool in exploring which set of targeted interventions could locally be implemented. Supplementary malaria control may be directed at areas, which are identified as at risk. For instance, areas with many people that work outdoors at night may need more focus in terms of vector control.

          Trial registration: Trialregister.nl NTR3496—SolarMal, registered on 20 June 2012

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          Most cited references 51

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          Geographically Weighted Regression: A Method for Exploring Spatial Nonstationarity

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            The changing epidemiology of malaria elimination: new strategies for new challenges.

            Malaria-eliminating countries achieved remarkable success in reducing their malaria burdens between 2000 and 2010. As a result, the epidemiology of malaria in these settings has become more complex. Malaria is increasingly imported, caused by Plasmodium vivax in settings outside sub-Saharan Africa, and clustered in small geographical areas or clustered demographically into subpopulations, which are often predominantly adult men, with shared social, behavioural, and geographical risk characteristics. The shift in the populations most at risk of malaria raises important questions for malaria-eliminating countries, since traditional control interventions are likely to be less effective. Approaches to elimination need to be aligned with these changes through the development and adoption of novel strategies and methods. Knowledge of the changing epidemiological trends of malaria in the eliminating countries will ensure improved targeting of interventions to continue to shrink the malaria map. Copyright © 2013 Elsevier Ltd. All rights reserved.
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              Urbanization, malaria transmission and disease burden in Africa.

              Many attempts have been made to quantify Africa's malaria burden but none has addressed how urbanization will affect disease transmission and outcome, and therefore mortality and morbidity estimates. In 2003, 39% of Africa's 850 million people lived in urban settings; by 2030, 54% of Africans are expected to do so. We present the results of a series of entomological, parasitological and behavioural meta-analyses of studies that have investigated the effect of urbanization on malaria in Africa. We describe the effect of urbanization on both the impact of malaria transmission and the concomitant improvements in access to preventative and curative measures. Using these data, we have recalculated estimates of populations at risk of malaria and the resulting mortality. We find there were 1,068,505 malaria deaths in Africa in 2000 - a modest 6.7% reduction over previous iterations. The public-health implications of these findings and revised estimates are discussed.
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                Author and article information

                Contributors
                tobiassolarmal@gmail.com , tobias.homan@wur.nl
                nicolas.maire@unibas.ch
                alexandra.hiscox@wur.nl
                aurelio.dipasquale@unibas.ch
                ibrahimkiche@yahoo.com
                kaonoka@yahoo.com
                cmweresa@icipe.org
                rmukabana@yahoo.co.uk
                amanda.ross@unibas.ch
                thomas-a.smith@unibas.ch
                willem.takken@wur.nl
                Journal
                Malar J
                Malar. J
                Malaria Journal
                BioMed Central (London )
                1475-2875
                4 January 2016
                4 January 2016
                2016
                : 15
                Affiliations
                [ ]Laboratory of Entomology, Wageningen University and Research Centre, Wageningen, The Netherlands
                [ ]Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland
                [ ]University of Basel, Basel, Switzerland
                [ ]Department of Medical Entomology, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
                [ ]School of Biological Sciences, University of Nairobi, Nairobi, Kenya
                Article
                1044
                10.1186/s12936-015-1044-1
                4700570
                © Homan et al. 2015

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                Funding
                Funded by: COmON Foundation
                Funded by: FundRef http://dx.doi.org/10.13039/501100005688, Gottfried und Julia Bangerter-Rhyner-Stiftung (CH);
                Funded by: Novartis Foundation for Medical Biological Research project
                Categories
                Research
                Custom metadata
                © The Author(s) 2016

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