Trends in Malaria Incidence and Predictive Factors before and after Campaign-Based Distribution of Standard and Next-Generation Insecticide-Treated Nets: An Observational Study Conducted in Kongo Central, Democratic Republic of the Congo

Abstract

Background: The incidence of malaria has risen globally, including in the DRC, despite repeated LLIN campaigns. In Kongo Central, five distribution cycles occurred from 2010 to 2023. In 2023, standard pyrethroid nets were replaced with next-generation PBO and IG2 nets. Methods: In this observational historical cohort study, we analyzed malaria incidence trends (2010-2024) and projections (2024-2030) across 31 health zones using exhaustive data from the National Health Information System, LLIN distribution records, and ERA5 climatic variables. Bivariate and multivariate panel data models (random effects and STATA v16) identified predictive factors. Results: Incidence rose progressively from 2010 to 2024 (mean, 266 cases/1000 individuals in the population; range, 47 - 765), with projections indicating continuation. Bivariate analyses showed temporary reductions one year post-distribution for both standard (deltamethrin 55 - 80 mg/m 2 ) and next-generation LLINs, but there was no sustained difference (RR 0.40 [95% CI 0.18 - 0.89] for 2011 for deltamethrin against 2023 PBO/IG2; p = 0.016). Multivariate panel models identified temperature (coef. 10.88, p = 0.02) and deforestation (coef. 7.94, p = 0.01) as drivers of the increase, and population density (coef. 0.09, p < 0.001) was found to be protective. Conclusion: The incidence of malaria is rising in the province, with both standard and next-generation nets providing only short-term reductions. Environmental factors like temperature and deforestation highlight the need for integrated control strategies as opposed to the use of nets alone.