Effectiveness of community-based burden estimation to achieve elimination of lymphatic filariasis: a comparative cross-sectional investigation in Côte d’Ivoire

For lymphatic filariasis (LF) elimination, endemic countries must document the burden of LF morbidity (LFM). Community-based screening (CBS) is used to collect morbidity data, but evidence demonstrating its reliability is limited. Recent pilots of CBS for LFM alongside mass drug administration (MDA) in Côte d’Ivoire suggested low LFM prevalence (2.1-2.2 per 10,000).We estimated LFM prevalence in Bongouanou District, Côte d’Ivoire, using a comparative cross-sectional design. We compared CBS implemented independently of MDA, adapted from existing Ministry of Health protocols, to a population-based prevalence survey led by formally trained nurses. We evaluated the reliability of case identification, coverage, equity, and cost of CBS.CBS identified 87.4 cases of LFM per 10,000; the survey identified 47.5 (39.4-56.3; prevalence ratio [PR] 1.84; 95% CI 1.64-2.07). CBS identified 39.7 cases of suspect lymphoedema per 10,000; the survey confirmed 35.1 (29.2-41.5) filarial lymphoedema cases per 10,000 (PR 1.13 [0.98-1.31]). CBS identified 100.3 scrotal swellings per 10,000; the survey found 61.5 (55.5-67.8; PR 1.63 [1.41-1.88]); including 26.6 (21.5-32.4) filarial hydrocoele per 10,000 (PR of suspect to confirmed hydrocele 3.77 [3.12-4.64]). Positive predictive values for case identification through CBS were 64.0% (54.5-72.8%) for filarial lymphoedema; 93.2% (88.5-96.4%) for scrotal swellings; and 33.3% (26.4-40.8%) for filarial hydrocoele. Households of lower socioeconomic status and certain minority languages were at risk of exclusion. Direct financial costs were $0.17 per individual targeted and $69.62 per case confirmed. We provide our CBS toolkit.Our community-based approach to LFM burden estimation appears scalable and provided reliable prevalence estimates for LFM, scrotal swellings and LF-lymphoedema. The results represent a step-change improvement on CBS integrated with MDA, whilst remaining at programmatically feasible costs. Filarial hydrocoele cases were overestimated, attributable to the use of case definitions suitable for mass-screening by informal staff. Our findings are broadly applicable to countries aiming for LF elimination using CBS.Summary boxWhat is already known?In many lymphatic filariasis (LF) endemic countries, community-based screening (CBS) is used alongside mass drug administration (MDA) campaigns to estimate the burden of disease (LFM), required to achieve WHO targets for disease elimination.Previous studies have shown that the accuracy of CBS for LFM varies widely and the underlying contextual factors that impact on effectiveness remain unclear.In Côte d’Ivoire in 2020, pilot studies alongside MDA suggested low prevalence of LFM, though a process evaluation indicated estimates were negatively affected due to the competing demands of MDA, a challenge reported in other settings.What are the new findingsWe strengthened CBS in Bongouanou Department, Côte d’Ivoire, and de-coupled activities from MDA, which led to a 40-fold increase in LFM case estimates. We validated this estimate using a population-based prevalence survey led by formal healthcare workers, which demonstrated a comparable estimate of LFM.The direct financial cost of CBS was comparable to, or less than, other large-scale NTD interventions and supports scalability as a programmatic activity.We quantified specific biases of CBS, including poor differentiation between hydrocoele and scrotum swellings of alternative aetiology, and preferential inclusion of household based on sociodemographic characteristics.What do the new findings implyThe approach we developed for strengthened, standalone CBS can provide estimates of LFM that reflect the true burden of disease, and is applicable to other LF endemic countries utilising large-scale community-based approaches.There is likely to be a high burden of LFM in endemic districts requiring expansion of morbidity management and disability prevention services.Accurate delineation of hydrocoele from other causes of scrotal swellings appears unfeasible using informal cadres employed during CBS. In settings where CBS is implemented, health providers should consider integration of conditions in activities.Public InvolvementTwo CDDs who had been involved in pilot LFM screening activities in 2020 participated in a review workshop, providing feedback which was used to develop the toolkit for LFM screening.Prior to the start of study activities, a launch meeting was held with traditional and religious leaders, administrative authorities and representatives of men’s, women’s and children’s groups of Bongouanou district. Participants were asked for their perspective on the importance of LFM as a health problem in their communities. Through this meeting they were informed about the CBS and nurse-led survey, and asked to cascade information through their communities.Patients were not involved in the study design.