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. 2024 Feb 8;18(2):e0011947.
doi: 10.1371/journal.pntd.0011947. eCollection 2024 Feb.

Spatial heterogeneity in mass drug administration from a longitudinal epidemiological study assessing transmission interruption of soil transmitted helminths in the Wolaita zone of southern Ethiopia (Geshiyaro Project)

Santiago Rayment Gomez  1 , Rosie Maddren  1 , Ewnetu Firdawek Liyew  2 , Melkie Chernet  2 , Ufaysa Anjulo  3 , Adugna Tamiru  3 , Getachew Tollera  2 , Geremew Tasew  2 , Birhan Mengistu  1 , Benjamin Collyer  1 , Kathryn Forbes  1 , Roy Anderson  1
Affiliations

Spatial heterogeneity in mass drug administration from a longitudinal epidemiological study assessing transmission interruption of soil transmitted helminths in the Wolaita zone of southern Ethiopia (Geshiyaro Project)

Santiago Rayment Gomez et al. PLoS Negl Trop Dis. .

Abstract

Objectives: Deworming programmes of soil-transmitted helminths are generally monitored and evaluated by aggregating drug coverage and infection levels at a district level. However, heterogeneity in drug coverage at finer spatial scales means indicators may remain above thresholds for elimination as a public health problem or of transmission in some areas. This paper aims to highlight the misleading information that aggregating data at larger spatial scales can have for programme decision making.

Methods: Drug coverage data from the Geshiyaro project were compared at two spatial scales with reference to the World Health Organisation's targets. District (woreda) and village (kebele) level were compared. The association between infection levels and drug coverage was analysed by fitting a weighted least-squares function to the mean intensity of infection (eggs per gram of faeces) against drug coverage.

Results: The data show clearly that when the evaluation of coverage is aggregated to the district level, information on heterogeneity at a finer spatial scale is lost. Infection intensity decreases significantly (p = 0.0023) with increasing drug coverage.

Conclusion: Aggregating data at large spatial scales can result in prematurely ceasing deworming, prompting rapid infection bounce-back. There is a strong need to define context-specific spatial scales for monitoring and evaluating intervention programmes.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Map of Ethiopia showing the location of the Geshiyaro study region in southwestern Ethiopia.
Coloured polygons in the inset map highlight the five districts that were censused and biometrically monitored. Shapefile data from GADM (https://gadm.org/download_country.html).
Fig 2
Fig 2. Maps of the Geshiyaro study region within the Wolaita zone.
(a) village level MDA coverage in pre-School Aged Children (Pre-SAC) populations; (b) standard error of MDA coverage; (c) villages that were above or below WHO’s target threshold for MDA coverage (75%); (d) the aggregated MDA coverage at the district level. Abbreviations: Pre-SAC–pre-school-aged children. Shapefile data from GADM (https://gadm.org/download_country.html).
Fig 3
Fig 3. Maps of the Geshiyaro study region within the Wolaita zone.
(a) village level MDA coverage in School Aged Children (SAC) populations; (b) standard error of MDA coverage; (c) villages that were above or below WHO’s target threshold (75%) for MDA coverage; (d) the aggregated MDA coverage at the district level. Abbreviations: SAC–school-aged children. Shapefile data from GADM (https://gadm.org/download_country.html).
Fig 4
Fig 4. Maps of the Geshiyaro study region within the Wolaita zone.
(a) village level MDA coverage in adult populations; (b) standard error of MDA coverage; (c) villages that were above or below WHO’s target threshold for MDA coverage; (d) the aggregated MDA coverage at the district level. Shapefile data from GADM (https://gadm.org/download_country.html).
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