Epidemiological and Clinical Profiling of Brucellosis Relapse and Complication Syndromes: Insights from a Registry in Western Iran

Introduction: Brucellosis manifests heterogeneously across endemic regions, with relapse and complication patterns remaining inadequately characterized. This study leverages a provincial registry to delineate syndrome-specific epidemiological and clinical profiles. Methods: A prospective cohort analysis of ۳۰ brucellosis cases confirmed by both serological testing and compatible clinical manifestations registered in Hamadan Province, Iran (۲۰۲۳–۲۰۲۴). Cases were stratified as Relapse-only (R) (۱۶.۶۷%), Complication-only (C) (۷۰%), or Relapse-Complication Syndrome (RC) (۱۳.۳۳%). Multivariate non-parametric analyses compared demographics, exposures, clinical features, and laboratory parameters. Results: Males predominated (۶۶.۷%), with mean age ۴۸.۹±۱۸.۹ years. Complication-only patients were older (۵۱.۲±۱۶.۸ vs. ۴۴.۴±۱۱.۱ in relapse; P=۰.۸۹۵). Occupational animal contact (۸۰%) and unpasteurized dairy consumption (۴۰%) were primary risks. Relapse-Complication Syndrome showed male predominance (۷۵%) and concentrated age distribution (۵۳–۶۲ years). Musculoskeletal complications dominated (۴۰% arthritis, ۴۰% spondylitis), disproportionately affecting lumbar vertebrae (۸۰%). Symptomatically, generalized pain (۹۳.۳%), fatigue (۸۳.۳%), and back pain (۷۳.۳%) were ubiquitous, while fever discriminated Relapse-Complication Syndrome (۷۵% vs. ۴۷.۶% in complications; P=۰.۵۶۰). Serology (Wright≥۱:۸۰ in ۹۰%) and inflammatory markers (ESR>۵۰mm/hr in ۳۲%) showed no syndromic discrimination. Novel incidence patterns emerged: highest relapse in Famenin males (۳۵.۷۱/۱۰۰۰), complications in Tuyserkan males (۵۷.۱۴/۱۰۰۰), and Relapse-Complication in Bahar females (۴۵.۴۵/۱۰۰۰). Conclusion: This registry-based syndromic stratification identifies distinct epidemiological phenotypes. The high complication burden despite treatment, geographic clustering, and dissociation between serology and clinical severity demand revised surveillance protocols and targeted prevention in agricultural communities.