Integrated one health surveillance reveals spatiotemporal dynamics and human–livestock concordance of brucellosis in northeastern Iran

Brucellosis remains a major bacterial zoonosis in endemic regions, sustained by infection in livestock and human exposure through direct animal contact and consumption of unpasteurized dairy products. This study evaluated the spatiotemporal patterns of human and livestock brucellosis in Razavi Khorasan Province, Iran, and assessed concordance between human and animal indicators within a One Health framework. A retrospective, record-based analysis was conducted using notified human brucellosis data (2016–2024) and provincial veterinary surveillance data for cattle and calves (2014–2024) and small ruminants (2023). Human incidence rates were calculated with year-specific mid-year population denominators and demographic associations were assessed using an effective-sample-size weighted chi-square approach. Annual bovine positive counts were modeled using negative binomial regression with the logarithm of the number tested as an offset. Small-ruminant seropositivity was estimated from the structured 2023 cross-sectional dataset using modified Rose Bengal testing followed by indirect ELISA, and animal- and herd-level correlates were evaluated using multivariable generalized estimating equations (GEE) with epidemiological-unit clustering. Temporal concordance between annual human incidence and annual bovine surveillance-based occurrence was assessed using Pearson correlation over the common observation period. Overall, 29,422 human brucellosis cases were reported, corresponding to a mean annual incidence of 47.7 per 100,000 population. Incidence increased significantly with age, peaking at 77.5 per 100,000 among individuals aged 45–<60 years (trend P < 0.001), and was markedly higher in rural compared with urban residents (125.5 vs. 19.6 per 100,000; P < 0.001). Incidence was numerically higher in men than women (51.6 vs. 43.4 per 100,000), with the prespecified effective-sample-size weighted comparison yielding P = 0.183. Reported exposures included animal contact (82.0%) and consumption of unpasteurized dairy products (71.1%), frequently occurring together (59.8%). Among 884,538 bovine tests performed, 939 were positive (overall surveillance-based test positivity 0.106%); negative binomial regression showed no significant monotonic temporal trend (IRR per calendar year = 1.01, 95% CI: 0.90–1.13, P = 0.861). Small-ruminant two-step seropositivity in the 2023 surveillance cycle was 17.3% (725/4,190) (95% CI: 16.2–18.5%). In the multivariable GEE analysis accounting for epidemiological-unit clustering, no evaluated animal- or herd-level covariate remained statistically significant. Across the common observation period, annual human brucellosis incidence showed a positive temporal correlation with annual bovine surveillance-based occurrence (Pearson r = 0.793; P = 0.011). County-level correlations between human incidence and bovine test positivity ( r = − 0.333, P = 0.072) and small-ruminant seropositivity ( r = − 0.103, P = 0.586) were not statistically significant; Global Moran’s I detected no significant spatial autocorrelation, and no Local Moran association remained significant after Bonferroni correction. Brucellosis remains endemic in Razavi Khorasan Province, with substantial human incidence, pronounced rural–urban and descriptive county-level variation, without statistically robust spatial clustering,, persistent evidence of infection in cattle and small ruminants, and a strong ecological temporal concordance between human and bovine surveillance signals. The bovine temporal result is based on an overdispersion-aware count model and does not establish causation or direct transmission. The 2023 small-ruminant result is a cross-sectional seropositivity estimate and cannot be interpreted as a temporal trend. Integrated One Health strategies should combine species-specific livestock surveillance and vaccination with food-safety measures and targeted risk communication in high-risk rural settings.