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Table 1 Variables used to analyse transmission risk

From: Rapid case-based mapping of seasonal malaria transmission risk for strategic elimination planning in Swaziland

Category

Variable

Input data

Manipulation

Predictors for high season

Predictors for low season

Weather

Rainfall

Monthly rainfall from 12 weather stations across the country

Ordinary kriging in R [28] to interpolate values across the country

Mean, minimum, maximum and summed monthly rainfall from November 2010 through February 2011

Mean, minimum, maximum and summed montly rainfall from March 2011 through October 2011

Temperature

Long-term averages, maximums, and minimums from WorldClim datasets [29]

 

Long-term average, maximum, and minimum temperature

Long-term average, maximum, and minimum temperature

Geography

Elevation and topography

90 m digital elevation model from the Radar Topography Mission [30, 31]

Topographic wetness index [32] calculated from the elevation map with the System for Automated Geoscientific Analyses (SAGA) [33]

Elevation, topographic wetness index

Elevation, topographic wetness index

Land cover

Vegetation

Landsat Enhanced Thematic Mapper (ETM) image from March 2009 with spatial resolution 30 m

Used to calculate the normalized difference vegetation index (NDVI) [24] and the modified normalized difference water index (NDWI) [25], as well as the distance to the grid-cells with highest (99.99th percentile) NDWI

NDVI, NDWI, distance to highest NDWI

NDVI, NDWI, distance to highest NDWI

Water bodies

Map of water bodies and irrigation zones from the Food and Agriculture Organization of the United Nations's Aquastat website [34], map of rivers from Diva GIS [35]

Distance to the nearest water body or irrigation zone and distance to nearest river calculated in ArcGIS [36]

Distance to nearest water body, distance to nearest river

Distance to nearest water body, distance to nearest river

Population

Population density

Gridded 100 m resolution population map from the AfriPop project [37, 38]

 

Population density

Population density

Vector control

Indoor residual spraying (IRS)

Date and number of houses covered by IRS in each of the 55 constituencies

Number of households receiving IRS in each region summed for the six months prior to each transmission season

Houses sprayed per population from July to December 2010

Houses sprayed per population from November 2010 to April 2011

Bed nets

Geolocations of all nets distributed since January 2010

All nets distributed before the start of each transmission summed at a 1 km resolution

Nets distributed per population from January to December 2010

Nets distributed per population from January 2010 to April 2011

Importation

Imported cases

Household locations of all identified imported cases

Distance to the nearest imported case household identified from two months prior to the start of the transmission season to two months prior to the end

Distance to the nearest of 89 imported case households identified from November 2010 to February 2011

Distance to the nearest of 54 imported case households identified from March to October 2011

  1. All variables were resampled to 100 sq m, producing maps with 2.4 million grid cells across the country.