Abstract
BackgroundMalaria infection and disease exhibit microgeographic heterogeneity which if predictable could have implications for designing small-area intervention. Here, the space-time clustering of Plasmodium falciparum infections using data from repeat cross-sectional surveys in Gezira State, a low transmission area in northern Sudan, is investigated.MethodsData from cross-sectional surveys undertaken in January each year from 1999-2009 in 88 villages in the Gezira state were assembled. During each survey, about a 100 children between the ages two to ten years were sampled to examine the presence of P. falciparum parasites. In 2009, all the villages were mapped using global positioning systems. Cluster level data were analysed for spatial-only and space-time clustering using the Bernoulli model and the significance of clusters were tested using the Kulldorff scan statistic.ResultsOver the study period, 96,022 malaria slide examinations were undertaken and the P. falciparum prevalence was 8.6% in 1999 and by 2009 this had reduced to 1.6%. The cluster analysis showed the presence of one significant spatial-only cluster in each survey year and one significant space-time cluster over the whole study period. The primary spatial-only clusters in 10/11 years were either contained within or overlapped with the primary space-time cluster.ConclusionThe results of the study confirm the generally low malaria transmission in the state of Gezira and the presence of spatial and space-time clusters concentrated around a specific area in the south of the state. Improved surveillance data that allows for the analysis of seasonality, age and other risk factors need to be collected to design effective small area interventions as Gezira state targets malaria elimination.
Highlights
Malaria infection and disease exhibit microgeographic heterogeneity which if predictable could have implications for designing small-area intervention
Plasmodium falciparum infection prevalence Over the period 1999 to 2009, 96,022 malaria slide examinations were undertaken among children aged between two to below ten years in 88 villages in Gezira state (Table 1)
At the start of the study period in 1999, 8.6% of the children examined were positive for P. falciparum infection and by 2009 this had reduced to 1.6% representing more than a five-fold decline in overall P. falciparum infection rates
Summary
Malaria infection and disease exhibit microgeographic heterogeneity which if predictable could have implications for designing small-area intervention. Malaria parasite transmission and clinical disease are characterized by important microgeographic variations, often between adjacent villages, households or families [1,2,3,4,5,6,7] This local heterogeneity is driven by a variety of factors including genetic [6,8], distance to potential breeding sites [9,10,11,12], housing construction [2,5,11,13,14], presence of domestic animals near the household [15,16], and socio-behavioural characteristics [3,10,11,17]. The spatial and temporal clustering of Plasmodium falciparum infections in 88 villages surveyed each year from 1999 to 2009 in the Gezira state, a generally very low unstable transmission area of the northern Sudan, is examined
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