Satellite images were used to construct a sampling frame for the random selection of households enrolled in prospective longitudinal and cross-sectional surveys of malaria parasitaemia in the catchment area of Macha Hospital in Southern Province, Zambia (Figure 1 ). Macha Hospital is approximately 70 km from the nearest town of Choma and the catchment area is populated by traditional villagers living in small, scattered homesteads. Anopheles arabiensis is the primary vector responsible for malaria transmission, which peaks during the rainy season from December through April [11 (link)]. The sampling frame for the random selection of households was constructed from a Quickbird™ satellite image obtained from DigitalGlobe Services, Inc. (Denver, Colorado). The image was imported into ArcGIS 9.2 (Environmental Systems Research Institute [ESRI], Redlands, California) and locations of households were identified and enumerated manually. Structures of appropriate size and shape were identified as potential residences, and consisted of one or more domestic structures where members of a family resided. Smaller structures, such as kraals, and larger structures, such as schools, were excluded. Selected households were allocated to one of two study cohorts: longitudinal and cross-sectional. Households in the longitudinal cohort were surveyed repeatedly approximately every two months and households in the cross-sectional cohort were surveyed once. Cross-sectional and longitudinal household surveys were conducted approximately every other month (during alternate months) from April 2007 through December 2007 in the first study area and from February 2008 through December 2008 in the second study area. Data from all cross-sectional households and the first longitudinal household visit were used to develop the spatial risk model. Model validation was conducted with the full longitudinal dataset. The study was approved the Johns Hopkins Bloomberg School of Public Health Institutional Review Board and the University of Zambia Research Ethics Committee.
A field team was provided with images and coordinates of the randomly selected households. After obtaining permission from the local chief and head of household, and individual written informed consent, a questionnaire was administered to each participant residing within the household and a blood sample was collected by finger prick. Rapid diagnostic tests (RDT; ICT Diagnostics, Cape Town, South Africa) were used to detect P. falciparum histidine-rich protein 2. This RDT was shown to detect 82% of test samples with wild-type P. falciparum at a concentration of 200 parasites/μL 98% of test samples with a concentration of 2,000 parasites/μL, with false positives in 0.6% of clean negative samples [12 ]. Individuals who were RDT positive were offered treatment with artemether-lumefantrine (Coartem®) by trained medical personnel. Households in which at least one individual tested positive by RDT were classified as a positive household. Positive and negative households were plotted as a data layer in ArcGIS 9.2.
A field team was provided with images and coordinates of the randomly selected households. After obtaining permission from the local chief and head of household, and individual written informed consent, a questionnaire was administered to each participant residing within the household and a blood sample was collected by finger prick. Rapid diagnostic tests (RDT; ICT Diagnostics, Cape Town, South Africa) were used to detect P. falciparum histidine-rich protein 2. This RDT was shown to detect 82% of test samples with wild-type P. falciparum at a concentration of 200 parasites/μL 98% of test samples with a concentration of 2,000 parasites/μL, with false positives in 0.6% of clean negative samples [12 ]. Individuals who were RDT positive were offered treatment with artemether-lumefantrine (Coartem®) by trained medical personnel. Households in which at least one individual tested positive by RDT were classified as a positive household. Positive and negative households were plotted as a data layer in ArcGIS 9.2.
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