Evaluation of the insecticide custody chain and its relationship with malaria burden in the Brazilian Amazon: a process and exploratory impact assessment (2019-2023)

BACKGROUND Malaria remains a major public health concern in Brazil, with the Amazon region accounting for 99.9% of the country’s cases. Indoor residual spraying (IRS) using Etofenprox 20% PM is a core vector control strategy. However, inefficiencies in the insecticide custody chain, including planning, storage, and distribution, may compromise intervention effectiveness.
OBJECTIVES This study aimed to evaluate the insecticide custody chain from a process perspective, identifying logistical bottlenecks, while also exploring potential impact by examining associations between insecticide allocation and malaria burden in Brazil and in three high-incidence municipalities in the state of Amazonas (Barcelos, Tefé, and São Gabriel da Cachoeira) from 2019 to 2023. The underlying hypothesis is that in a well-functioning system, insecticide distribution should be correlated with malaria risk determinants, such as epidemiological and environmental variables, rather than merely responding to reported case counts.
METHODS A mixed-methods approach was used. Quantitative analysis applied Pearson correlation, simple and multiple linear regressions (with time-lag), and ARIMA models to evaluate associations between insecticide volume and malaria cases, incorporating environmental and demographic covariates. A complementary qualitative assessment, based on a structured risk matrix, examined failures across four stages of the custody chain: planning, storage, application, and monitoring.
FINDINGS At the national level, insecticide volume was significantly associated with malaria cases (β = 0.161; p = 0.038;
R² = 0.74) and deforestation (β = 0.626; p = 0.034). Time-series analysis revealed a reactive pattern, with insecticide allocation often lagging behind malaria incidence peaks. In the municipalities studied, models lacked statistical significance, but trends suggested weak local planning and disconnects from risk-based forecasting. The risk matrix revealed systemic weaknesses, including limited data interoperability, insufficient integration of environmental indicators, and poor federal coordination.
MAIN CONCLUSIONS The current custody chain functions reactively and lacks integration with surveillance and predictive environmental data, contradicting World Health Organization (WHO) recommendations. Structural reforms are urgently needed. These include: (i) risk-based planning incorporating environmental variables, (ii) interoperable information systems, (iii) improved surveillance of vector resistance, and (iv) intergovernmental agreements for equitable and efficient resource allocation. Findings highlight the need for strategic reorientation of IRS logistics toward anticipatory and data-driven planning. Strengthening the custody chain through intersectoral coordination and environmental intelligence is essential not only to improve operational efficiency but also to increase the cost-effectiveness and epidemiological impact of malaria control interventions in the Amazon. Lessons learned may inform broader efforts in other endemic regions aiming for malaria elimination.