Epidemiological trends, health inequality, and forecasting of Brucellosis in Mainland China, 2004-2030

Brucellosis poses a significant global public health challenge. However, owing to insufficient long-term data, the complete epidemiological landscape and health inequalities in Mainland China have yet to be fully elucidated. Therefore, this study aimed to systematically assess the incidence, temporal trends, spatiotemporal patterns, and socioeconomic disparities related to brucellosis in Mainland China.

Utilizing national human brucellosis reporting data from 2004 to 2024, a comprehensive epidemiological analysis was conducted. Descriptive epidemiological methods were employed to characterize the epidemic features and fitted Joinpoint regression models to calculate the annual percent change (APC) and average annual percent change (AAPC), quantifying trends over time. Seasonality was evaluated using seasonal indices and circular distribution methods to identify peak periods and case concentration. Spatiotemporal scan statistics were applied to identify high-risk clusters (hotspots) of disease distribution. The slope index of inequality (SII) and concentration index (CI) were calculated to assess health disparities associated with regional income levels. Autoregressive integrated moving average models were constructed to predict monthly incidence rates and future trends.

From 2004 to 2024, a total of 888,954 cases of brucellosis were reported in Mainland China, yielding an average annual incidence of 3.11 per 100,000 population. Cases were primarily concentrated in pastoral (42.43%) and agro-pastoral (43.36%) regions, with an alarming upward trend in agricultural regions observed recently. The epidemic demonstrated notable seasonality, peaking from mid-February to late August, with the highest incidence in mid-May. Nevertheless, the intensity of this seasonality weakened progressively over time (β =- 0.869, P < 0.0001). Overall, between 2004 and 2024, the incidence rate of human brucellosis in Mainland China increased (AAPC = 8.54%; 95% confidence interval (CI): 3.74-13.56), characterized by three distinct phases: a rapid increase (2004-2014, APC = 14.46%), a brief decline (2014-2018, APC = -9.54%), and a subsequent resurgence (2018-2024, APC = 12.17%). Notably, incidence rates increased considerably in the southern (AAPC = 35.66%), eastern (AAPC = 21.89%), northeastern (AAPC = 21.88%), and central (AAPC = 19.30%) regions of China. 24 provinces (including autonomous regions and municipalities) exhibited increasing incidence rates. Spatiotemporal scan statistics identified a primary cluster (2015-2024; six northwestern provinces [encompassing autonomous regions and municipalities]; relative risk (RR) = 12.94; log-likelihood ratio (LLR) = 393,077.07; P < 0.001) and two secondary clusters. Health inequality analysis revealed significantly higher brucellosis risk in low-income regions (CI = -0.291; SII = -5.44; 95% CI: -14.94-4.07). Predictions based on current trends suggest an overall increase in brucellosis incidence in Mainland China from 2025 to 2030, with a projected peak of 0.72 per 100,000 (95% CI: 0.54-0.89) in July 2030.

From 2004 to 2024, brucellosis in Mainland China has demonstrated an upward trend, characterized by a persistent yet evolving spatial "north-south diffusion" pattern and diminishing seasonality. Ecological analyses revealed a consistent negative association between provincial income and incidence, reflecting a macro-level disparity wherein low-income regions bear a heavier disease burden. If transmission patterns and current control intensity persist, the incidence is predicted to increase persistently through 2030. Consequently, context-specific interventions are essential.High-incidence regions should prioritize source control, proactive screening of high-risk populations, and behavioral interventions to limit further transmission, whereas low-incidence regions should concentrate on preventing imported cases through strengthened surveillance and rapid outbreak response.