A Multi-model Counterfactual Analysis of Human Brucellosis in China: Spatiotemporal Epidemiology and Heterogeneous Pandemic-associated Deviations in 2020.

OBJECTIVES: This study examined long-term spatiotemporal patterns of human brucellosis in China and assessed whether reported incidence in 2020 differed from expected levels during the COVID-19 pandemic. METHODS: We analyzed surveillance data from 31 provincial-level regions in mainland China from 2004 to 2020. Joinpoint regression assessed national trends. Seasonal indices, spatial autocorrelation, and space-time scan statistics were used to examine monthly variation and geographic clustering. Province-specific forecasting models estimated expected case counts. RESULTS: National incidence increased from 2004 to 2014 and declined thereafter, with an overall average annual percent change (AAPC) of 6.03% across the full 2004-2020 study period. Cases regularly peaked from March to July. Farmers and herders accounted for most cases, while adults aged ≥45 years represented an increasing share. Persistent hotspots were concentrated in northern pastoral and agro-pastoral provinces. The largest space-time cluster included Inner Mongolia and Shanxi during 2008-2015. In 2020, observed cases varied from forecast levels across provinces and seasons. Qinghai and Anhui showed excess cases in both peak and non-peak seasons, while Guizhou exhibited more pronounced excess in the non-peak season; by contrast, Heilongjiang reported consistently fewer cases than expected. CONCLUSIONS: Human brucellosis in China remains seasonal, spatially concentrated, and increasingly linked to older livestock workers. Prevention should focus on persistent endemic hotspots, periods of intensified livestock-related exposure, particularly the livestock birthing season, and sustained surveillance capacity during public health emergencies.