Resurgence of Human Brucellosis in Khuzestan Province, Southwestern Iran: Epidemiological Trends From 2017 to 2024
Brucellosis is a neglected zoonosis with a considerable disease burden in livestock‐dependent areas. Khuzestan Province, southwestern Iran, exhibits diverse ecological and agricultural landscapes that may drive heterogeneous transmission. Knowledge of recent epidemiological trends is important for targeted control. We aimed to characterize the temporal and demographic patterns of human brucellosis in Khuzestan from 2017 to 2024, with emphasis on changes observed after 2021. We analyzed aggregated surveillance data for all laboratory‐confirmed human brucellosis cases reported in Khuzestan Province between 2017 and 2024. Crude annual incidence rates were calculated using population denominators linearly interpolated from the 2017 census and the 2023 official estimate. Log‐linear trend regression, performed using Joinpoint software, estimated the annual percentage changes (APCs) in incidence case counts. Poisson′s regression with population offset quantified period relative risks (RRs) comparing 2022–2024 with 2017–2021. Chi‐square tests assessed temporal shifts in distributions across age groups (15 categories), sex, residence (rural/urban/nomadic), and four geographical zones (Northern Highlands, Central Plains, Southern Coastal and Marshland, and Western Borderlands). A total of 3923 cases were reported. Crude incidence remained stable at 7.9–8.1 per 100,000 during 2017–2019, declined to 6.3–7.0 in 2020–2021, and then increased sharply to 12.3–14.7 in 2022–2024 (APC = +10.7%; 95% CI: 2.2–19.9; p = 0.019). Incidence during 2022–2024 was 1.66 times higher than during 2017–2021 (95% CI: 1.52–1.81; p < 0.001). The largest relative increases in reported case counts were in adults aged ≥ 70 years (APC = +21.1%; 95% CI: 11.1–32.2) and in adults aged 65–69 years (+20.0%, 9.9–31.1), whereas children aged 0–4 years showed no significant change. The male‐to‐female ratio shifted from 0.88 in 2017 to 1.22 in 2024 (p = 0.032), driven by a significant rise in male cases (APC = +11.5%, p = 0.011) against a nonsignificant female increase. Rural cases increased significantly (APC = +11.2%, p = 0.009), accounting for 47%–61% of annual cases. The Northern Highlands zone bore 62.7% of total cases (APC = +11.6%, p = 0.003); the Southern Coastal zone exhibited the steepest relative increase (APC = +15.8%, p = 0.020). Although statistically significant, changes in composition over time were small in magnitude (Cramér′s V = 0.06 − 0.12). Human brucellosis in Khuzestan Province has resurged dramatically since 2021, with a 66% increase in period risk. The epidemiological profile shifted to older adults, males, and people living in rural areas, with marked geographical heterogeneity. The results emphasize the need for targeted vaccination of livestock in high‐burden areas (Northern Highlands and Southern Coastal), enhanced surveillance in older age groups, and increased One Health approaches to reverse this trend.