Mass drug administration coverage and its determinants for the elimination of onchocerciasis in Ulanga District, Tanzania.

Background: Onchocerciasis remains an important public health problem targeted for elimination in Tanzania. Ulanga District was hyperendemic for onchocerciasis before the intervention, underscoring the need for particularly high coverage in MDA efforts. The district has been implementing MDA through Community Directed Treatment with Ivermectin (CDTI) strategy since 1998. However, there is preliminary evidence of persistent onchocerciasis transmission, which likely sustains the observed high prevalence of Onchocerciasis in both human and vector species. This could be linked to poor treatment coverage. This study was conducted to assess treatment coverage and explore factors that determine drug uptake during MDA program.

Methods: A cross-sectional study was conducted in Ulanga District, Morogoro, Tanzania, from April to June 2019. Using multistage cluster sampling, 502 participants were randomly selected and interviewed through a structured questionnaire. Modified Poisson regression analysis was used to identify independent factors affecting MDA uptake.

Results: The overall response rate was 96% with majority (67%) of respondents being females, and the mean age of the study participants was 37.8 years with a standard deviation (SD) of ± 15 years. The study found that MDA coverage varied across villages: Mawasiliano (68%, CI: 59.3 - 75.6), Uponera (83%, CI; 76.6 - 89.6), Isongo (84.8%, CI: 77.3 - 90.1) and Togo (79%, CI: 70.1 - 85.8). While Uponera and Isongo achieved the WHO-recommended 80% coverage for transmission interruption, Mawasiliano and Togo fell below this threshold. Age significantly influenced drug uptake, with younger individuals (15-24 years) having a lower uptake rate [APR = 2.8, p = 0.008], followed by the 25-34 age group [APR = 2.3, p = 0.04]. Occupation also played a role, as small and medium enterprise (SME) workers [APR = 3.2, p = 0.05] and students [APR = 2.9, p = 0.05] were less likely to participate. Residence duration in the village was a strong predictor of MDA uptake. Individuals living in the village for more than a year were significantly more likely to participate [APR = 2.3, p = 0.00]. Additionally, a lack of awareness about MDA benefits negatively impacted participation, as those uncertain about its benefits were less likely to take the drug [APR = 2.5, p = 0.03]. Similarly, individuals unaware of the correct MDA distribution schedule had lower uptake [APR = 2.5, p = 0.03]. However, those who took Ivermectin for prevention purposes were significantly more likely to participate [APR = 13.4, p = 0.001].

Conclusions: MDA coverage below the WHO optimally recommended coverage has been demonstrated in the villages studied. This implies low drug uptake, delayed interruption of transmission and Onchocerciasis elimination. The findings highlight the need for targeted interventions to improve MDA coverage by focusing on younger individuals, certain occupational groups, and new residents. Strengthening community engagement, improving health communication, and intensifying biannual MDA efforts are recommended to accelerate Onchocerciasis elimination in the district. It also underscores the need for adopting other effective public health interventions such as community mobilization towards slash and clear of potential breeding sites for Onchocerciasis vector.