Optimal survey designs for targeting chemotherapy against soil-transmitted helminths: effect of spatial heterogeneity and cost-efficiency of sampling - PubMed (original) (raw)

Optimal survey designs for targeting chemotherapy against soil-transmitted helminths: effect of spatial heterogeneity and cost-efficiency of sampling

Hugh J W Sturrock et al. Am J Trop Med Hyg. 2010 Jun.

Abstract

Implementation of helminth control programs requires information on the distribution and prevalence of infection to target mass treatment to areas of greatest need. In the absence of data, the question of how many schools/communities should be surveyed depends on the spatial heterogeneity of infection and the cost efficiency of surveys. We used geostatistical techniques to quantify the spatial heterogeneity of soil-transmitted helminths in multiple settings in eastern Africa, and using the example of Kenya, conducted conditional simulation to explore the implications of alternative sampling strategies in identifying districts requiring mass treatment. Cost analysis is included in the simulations using data from actual field surveys and control programs. The analysis suggests that sampling four or five schools in each district provides a cost-efficient strategy in identifying districts requiring mass treatment, and that efficiency of sampling was relatively insensitive to the number of children sampled per school.

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Figures

Figure 1.

Locations of the countries included in the study (inset map) and locations of schools from the datasets included in the study (main map).

Figure 2.

Map of Kenya showing province boundaries (inset map) and locations of 6,899 mixed public primary schools in Western, Nyanza, and Coast provinces (main map). The size and position of Western and Nyanza provinces are not in relation to Coast Province.

Figure 3.

Semi-variograms and best-fitted lines of spatial models for soil-transmitted helminths Ascaris lumbricoides and Trichuris trichiura in A, Kenya; B, Uganda and northern Tanzania > 2° south; C, Uganda and northern Tanzania < 2° south; and D, Zambia; and hookworm in A, Kenya; B, Uganda and Tanzania; and C, Zambia. Vertical axis indicates semi-variance and horizontal axis indicates distance in decimal degrees. Range in kilometers was calculated assuming 1 decimal degree = 112 km at the equator.

Figure 4.

A, Relationship between the number of schools surveyed and the ability to correctly classify districts according to treatment strategy in Coast, Nyanza, and Western provinces, based on conditionally simulated data from Kenya data and variograms (Coast, Western 1 and Nyanza 1) and Uganda data and variograms (Western 2 and Nyanza 2). Results are averaged over the different numbers of children sampled per school because there was little effect of sample size. B, Cost implications of different sampling strategies, averaged across different number of children per school, using a treatment cost of $0.15 per person and considering one year of treatment.

Figure 5.

Cost per district of the different sampling strategies (dark gray) and the cost of unnecessary treatment in those districts incorrectly classified in a higher endemicity class and requiring mass treatment, when mass treatment was not required (light gray) in Coast Province, Kenya, assuming treatment costs of $0.15 over one year. The solid lines represent 60 children per school and the dashed lines represent 10 children per school.

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Optimal survey designs for targeting chemotherapy against soil-transmitted helminths: effect of spatial heterogeneity and cost-efficiency of sampling - PubMed (original) (raw)