Long-term trends in urban scorpionism under mechanical and chemical control in a Brazilian municipality

Urban scorpionism is a persistent public health challenge in medium-sized Brazilian cities. While mechanical capture is routinely employed for surveillance, chemical control was reintroduced in November 2019 to intensify interventions in high-risk microenvironments. We conducted a longitudinal observational study using monthly aggregated data (January 2014–December 2024). Interrupted time-series analysis with segmented regression was used to evaluate temporal trends, seasonality and post-intervention changes. Mechanical capture intensity was included with 0-, 3- and 6-month lags. Robust standard errors were calculated using Newey–West corrections. Scorpion sting accidents remained present year-round, with predictable seasonal peaks despite sustained mechanical control. Lagged capture analyses showed no significant association with accident counts, indicating that captures primarily reflect operational effort. The November 2019 introduction of targeted chemical control was associated with an immediate level reduction of − 7.40 accidents (95% CI −13.73 to − 1.07; p = 0.022) and a significant negative change in slope (− 0.277 accidents/month; 95% CI −0.445 to − 0.110; p = 0.001). Comparison with the counterfactual projection showed divergence between observed and expected trajectories, corresponding to an estimated cumulative difference of 1,001 cases between November 2019 and December 2024 (30.9% reduction relative to the expected continuation of the pre-intervention trend). Integrated mechanical and focal chemical control were associated, in segmented regression analyses, with reductions in both level and slope of scorpion sting incidence after 2019, consistent with attenuation of the previously observed upward trend without evidence of abrupt disruption of seasonal dynamics. Surveillance indicators reflect sustained operational activity, while chemical interventions may contribute to targeted risk reduction within persistently affected urban settings.