Immunity to poliovirus in Afghanistan: A household sampling method for serological assessment based on geographical information systems

Abstract

Afghanistan continues to experience challenges affecting polio eradication. Mass polio vaccination campaigns, which aim to protect children under the age of 5, are a key eradication strategy. To date, the polio program in Afghanistan has only employed facility-based seroprevalence surveys, which can be subject to sampling bias. We describe the feasibility in implementing a cross-sectional household poliovirus seroprevalence survey based on geographical information systems (GIS) in three districts. Digital maps with randomly selected predetermined starting points were provided to teams, with a total target of 1,632 households. Teams were instructed to navigate to predetermined starting points and enrol the closest household within 60 m. To assess effectiveness of these methods, we calculated percentages for total households enrolled with valid geocoordinates collected within the designated boundary, and whether the Euclidean distance of households were within 60 m of a predetermined starting point. A normalized difference vegetation index (NDVI) image ratio was conducted to further investigate variability in team performances. The study enrolled a total of 78% of the target sample with 52% of all households within 60 m of a pre-selected point and 79% within the designated cluster boundary. Success varied considerably between the four target areas ranging from 42% enrolment of the target sample in one place to 90% enrolment of the target sample in another. Interviews with the field teams revealed that differences in security status and amount of non-residential land cover were key barriers to higher enrolment rates. Our findings indicate household poliovirus seroprevalence surveys using GIS-based sampling can be effectively implemented in polio endemic countries to capture representative samples. We also proposed ways to achieve higher success rates if these methods are to be used in the future, particularly in areas with concerns of insecurity or spatially dispersed residential units.

Figure 1.. Kandahar province: GPEI administrative levels.

Figure 2.. Nangahar province: GPEI administrative levels.

Figure 3.. Environmental surveillance in Kandahar, Jalalabad and Behsud. Delineation of catchment and non-catchment areas, all areas in ES catchment.

Figure 4.. Pilot test site, Azam Basti, Malir, Karachi district.

Figure 5.. Kandahar and Jalalabad team performances.

Figure 6.. Presence and absence of vegetation pixels in Kandahar. A: shown by the Normalized Difference Vegetation Index (NDVI); B: shown as a Boolean image.

Figure 7.. Presence and absence of vegetation pixels in Jalalabad and Behsud. A: shown by the Normalized Difference Vegetation Index (NDVI); B: shown as a Boolean image.

Figure 8.

Spread of vegetation pixel counts per cluster for catchment and non-catchment areas in Kandahar, Jalalabad and Behsud. Box and whisker plot where the line dividing the middle of the shaded boxplot is the median of all data values in the range. The shaded box contains the interquartile range (IQR) and depicts the bottom 25% (dark grey) and top 25% (light grey). Data points contained within the lower and upper whiskers represent 1.5 times the minimum and maximum of the IQR. Data points beyond the whiskers represent outliers.