Significant gap between Point participation and long‑term treatment adherence: An evaluation of ivermectin MDA in the Kwanware‑Ottou persistent onchocerciasis transmission focus, Wenchi, Ghana

TL;DR

Despite long-term ivermectin treatment, onchocerciasis transmission persists in Ghana due to low long-term adherence, with high recent participation masking poor sustained coverage.

Contribution

The study reveals a significant gap between recent and long-term treatment adherence in ivermectin MDA, using a novel approach combining satellite imagery and census data.

Findings

Point participation in ivermectin MDA was 80.3%, but effective participation (≥10 rounds) was only 53.5%.

Effective participation was strongly inversely correlated with infection prevalence (-0.74 for microfilariae, -0.79 for anti-Ov16 seroprevalence).

Remote settlements and mobile populations had lower effective participation, contributing to ongoing transmission.

Abstract

Despite more than 27 years of ivermectin mass drug administration (MDA), onchocerciasis transmission persists in the Kwanware-Ottou focus within the Wenchi Health District of Ghana. This study examined participation in ivermectin MDA over time in this transmission focus.

In March 2024, two months after MDA using the community-directed treatment with ivermectin (CDTI) approach, settlements within Kwanware-Ottou focus were identified through community consultations and satellite imagery. A census was then conducted integrating an ivermectin treatment coverage evaluation survey (CES) to evaluate community participation in CDTI. Data were cleaned using STATA and analysed in R. Descriptive statistics, multiple logistic regression, and ordinal logistic regression were conducted to examine factors associated with point and effective participation in CDTI. Point participation is the percentage of individuals aged 15 + who took ivermectin during the last CDTI, while effective participation refers to those who have taken it at least ten times in past rounds. Pearson correlation was used to assess the relationship between participation and infection prevalence.

Nineteen settlements were identified, with an overall point participation of 80.3% (n = 1461 participants; 95% Confidence Interval, CI:78.6 - 82) for the preceding CDTI. However, 10 settlements had coverage below 80%. Effective participation was only 53.5% (n = 974; CI: 51.2 -55.9), well below the recommended 80%. Participation was influenced by factors such as age, occupation, ethnicity, remoteness, length of stay in the settlement, and mobility (migration). Effective participation was correlated with infection levels, with correlation coefficients of -0.74 for microfilariae prevalence and -0.79 for anti-Ov16 seroprevalence, indicating a strong inverse relationship.

High point participation masks low effective participation and insufficient subdistrict geographical coverage. Conducting exhaustive CES in delineated foci is essential for evaluating CDTI performance, tailoring and strengthening CDTI, and informing alternative strategies to interrupt onchocerciasis transmission. This approach has contributed to effective, context-specific strategies to interrupt transmission in Wenchi and beyond.

Onchocerciasis or river blindness transmission persists in parts of Ghana despite decades of treatment with ivermectin via mass drug administration (MDA). This study focused on the Kwanware-Ottou transmission hotspot, where infection persists despite long-term treatment efforts. Using satellite imagery and settlement consultation, we identified 19 settlements and conducted a comprehensive survey to assess both recent and long-term participation in MDA. We found that while many individuals reported recent treatment during the last MDA round (80.3%), only about half had participated in enough rounds to meet elimination targets. Mobile populations and residents of remote settlements were particularly underserved. Our findings show that high reported coverage during a given MDA round can mask critical gaps in effective MDA participation in the long-term, which are strongly linked to ongoing transmission. We recommend evaluating both point and effective MDA participation in areas with inadequate treatment coverage or persistent transmission. This has contributed to commendable, tailored strategies to interrupt onchocerciasis transmission in Wenchi and beyond.

Figures