Socioeconomic Health Equity with Malaria Burden: Quantifying Slope (Relative) Index of Inequity in Malaria Infection Outcomes in the Southeastern-coastal Tanzania

Background Malaria remains a significant public health challenge in Tanzania, with socioeconomic factors playing crucial roles in disease outcomes. While previous studies have explored the relationship between socioeconomic status and malaria infection, quantitative assessment of equity condition in malaria outcomes remains understudied. This study innovatively applies Slope Index of Inequality (SII) and Relative Index of Inequality (RII) to quantify the equity conditions between socioeconomics and malaria burden in three Districts located in the Southeastern coast of Tanzania. Methods Data from the baseline survey of the China-Tanzania Demonstration Project on Malaria Control conducted in 2019 were analyzed. Key variables included: 1) socioeconomic status quantified through Principal Component Analysis incorporating household infrastructure, asset ownership, and social potential; 2) malaria infection outcomes, including blood test results, treatment costs, and days absent from work/education (days off). Logistic and linear regression analyses were performed to assess socioeconomic impacts, while SII and RII were calculated to measure health equity conditions across socioeconomic strata in three districts of Rufiji, Kilwa, and Kibiti. Results Higher socioeconomic status was associated with a lower risk of malaria infection (OR = 0.9975, 95% CI: 0.9972–0.9978), lower treatment costs (coefficient = -3.13, P < 0.05), and fewer days off work (coefficient = -0.0017, P < 0.05). Rufiji district demonstrated the most significant socioeconomic equality in malaria infection risk (SII=-12.62%, 95%CI: -17.19% to -8.06%; RII = 1.28, 95%CI: 1.12 to 1.55), treatment cost (SII = 837.769, 95%CI: -1182.44 to -491.75; RII = 1.30, 95%CI: 1.09 to 1.63) and days off (SII=-0.46, 95%CI: -0.62 to -0.30; RII = 1.21, 95%CI: 1.05 to 1.46). Conclusion The findings highlight significant socioeconomic disparities in malaria-related outcomes across the studied districts, emphasizing the need for targeted public health interventions to address inequities. By prioritizing equity-focused policies, such as enhanced access to prevention and treatment, Tanzania can make strides toward more inclusive malaria control and health system strengthening, particularly for the most vulnerable populations. Furthermore, the use of SII and RII offered a nuanced understanding of health disparities across the socioeconomic spectrum.