Characteristics of persistent hotspots of Schistosoma mansoni in western Côte d’Ivoire

Background: Preventive chemotherapy with praziquantel is the cornerstone of schistosomiasis control. However, in some social-ecological settings, the prevalence and/or intensity of Schistosoma infection does not lower meaningfully despite multiple rounds of preventive chemotherapy, a phenomenon termed persistent hotspot (PHS). We assessed the characteristics of PHS in a Schistosoma mansoni -endemic area of Côte d’Ivoire. Methods In October 2016, a cross-sectional parasitological survey was conducted in 14 schools in the western part of Côte d’Ivoire, one year after multiple rounds of preventive chemotherapy. In each school, 50 children aged 9-12 years were randomly selected and invited to submit two stool samples and one urine sample. Stool samples were subjected to triplicate Kato-Katz thick smears for S. mansoni diagnosis. Urine samples were examined by a filtration method for S. haematobium eggs. PHS was defined as failure to achieve a reduction in the prevalence and/or intensity of S. mansoni infection of at least 35% and 50%, respectively after multiple rounds of preventive chemotherapy targeting school-aged children. A questionnaire was administered in six schools to obtain data on demographic characteristics, including human-water contact behaviours, water, sanitation and hygiene and history of preventive chemotherapy. A malacological survey was conducted in December 2016. Results The overall prevalence of S. mansoni and S. haematobium in the 14 surveyed schools was 9.5% and 2.6%, respectively. There were four PHS among six schools that underwent detailed investigation. The S. mansoni prevalence in the four PHS was 10.9% (95% confidence interval (CI): 6.4-15.5%), compared to 6.6% (95% CI: 1.4-11.8%) in the remaining two schools. The arithmetic mean of S. mansoni eggs per gram of stool (EPG) among infected children was 123.8 EPG in PHS and 18.7 EPG in the remaining two schools. A statistically significant difference between PHS and the other schools regarding praziquantel coverage was found with higher coverage rate observed in PHS (98.4% versus 89.0%, X 2 = 3.7, p = 0.001). There was no significant difference with regard to access to clean water in the two groups of schools. Children bathing in open freshwater bodies were at higher odds of S. mansoni infection (odds ratio (OR) = 4.5, 95% CI: 1.6-12.6). A total of 76 human-water contact sites (53 in PHS and 23 in the other schools) were examined and 688 snails were collected, including 92 Biomphalaria pfeifferi , 25 Bulinus forskalii , 16 Bu. globosus and one Bu. truncatus . Conclusion Children in PHS schools bathed more frequently in open freshwater bodies, and hence, they were potentially more exposed to S. mansoni . Our findings call for an integrated control approach, complementing preventive chemotherapy with behavioural change implementation in PHS settings.