title: Elevated dry-season malaria prevalence associated with fine-scale spatial patterns of environmental risk: a case-control study of children in rural Malawi.
abstract: BACKGROUND
  Understanding the role of local environmental risk factors for malaria in holo-endemic, poverty-stricken settings will be critical to more effectively implement- interventions aimed at eventual elimination. Household-level environmental drivers of malaria risk during the dry season were investigated in rural southern Malawi among children < five years old in two neighbouring rural Traditional Authority (TA) regions dominated by small-scale agriculture.
  
  
  METHODS
  Ten villages were randomly selected from TA Sitola (n = 6) and Nsamala (n = 4). Within each village, during June to August 2011, a census was conducted of all households with children under-five and recorded their locations with a geographic position system (GPS) device. At each participating house, a nurse administered a malaria rapid diagnostic test (RDT) to children under five years of age, and a questionnaire to parents. Environmental data were collected for each house, including land cover within 50-m radius. Variables found to be significantly associated with P. falciparum infection status in bivariate analysis were included in generalized linear models, including multivariate logistic regression (MLR) and multi-level multivariate logistic regression (MLLR). Spatial clustering of RDT status, environmental factors, and Pearson residuals from MLR and MLLR were analysed using the Getis-Ord Gi* statistic.
  
  
  RESULTS
  Of 390 children enrolled from six villages in Sitola (n = 162) and four villages in Nsamala (n = 228), 45.6% tested positive (n = 178) for Plasmodium infection by RDT. The MLLR modelled the statistical relationship of Plasmodium positives and household proximity to agriculture (<25-m radius), controlling for the child sex and age (in months), bed net ownership, elevation, and random effects intercepts for village and TA-level unmeasured factors. After controlling for area affects in MLLR, proximity to active agriculture remained a significant predictor of positive RDT result (OR 2.80, 95% CI 1.41-5.55). Mapping of Pearson residuals from MLR showed significant clustering (Gi* z > 2.58, p < 0.01) predominantly within TA Sitola, while residuals from MLLR showed no such clustering.
  
  
  CONCLUSIONS
  This study provides evidence for significant, dry-season heterogeneity of malaria prevalence strongly linked to peridomestic land use, and particularly of elevated risk associated with nearby crop production.
authors.affiliation: Department of Epidemiology, School of Public Health, University of Michigan, 48104 Ann Arbor, MI, USA. lintow@umich.edu.
authors.forename: Lindsay R
authors.initials: LR
authors.lastname: Townes
authors.forename: Dyson
authors.initials: D
authors.lastname: Mwandama
authors.forename: Don P
authors.initials: DP
authors.lastname: Mathanga
authors.forename: Mark L
authors.initials: ML
authors.lastname: Wilson
mesh_terms: D016022:Case-Control Studies; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000175:diagnosis / Q000453:epidemiology*; D008295:Malawi / Q000453:epidemiology; D008297:Male; D010963:Plasmodium falciparum / Q000302:isolation & purification*; D015995:Prevalence; D012307:Risk Factors; D012424:Rural Population; D012621:Seasons; D062206:Spatial Analysis; D011795:Surveys and Questionnaires