University of Tabriz Journal of Zoonotic Diseases 2476-535X 10 2 2026 06 01 High prevalence of Coxiella burnetii coinfection in brucellosis patients: Molecular evidence from an endemic region in Iran 1171 1182 21820 10.22034/jzd.2026.21820 EN Zahra Montaseri Department of Infectious Diseases, School of Medicine, Fasa University of Medical Sciences, Fasa, Iran Maryam Ghasemzadeh Student Research Committee, Fasa University of Medical Sciences, Fasa, Iran Abbas Abdollahi Department of Bacteriology, School of Medicine, Fasa University of Medical Sciences, Fasa, Iran Maryam Montaseri Department of Food Hygiene and Public Health, School of Veterinary Medicine, Shiraz University, Shiraz, Iran 0000-0002-0533-1648 Mahmoud Agholi Department of Parasitology and Mycology, Fasa University of Medical Sciences, Fasa, Iran Mehdi Sharafi Department of Epidemiology, School of Public Health, Shiraz University of Medical Sciences, Shiraz, Iran Journal Article 2026 04 19 Brucellosis and Q fever are important zoonotic diseases with overlapping clinical manifestations.  Their concurrent occurrence is limited in Iran. This study investigated the prevalence and molecular characteristics of <em>Coxiella burnetii </em>infection among brucellosis patients in Fars province, Southwest Iran.<strong> </strong>A total of 152 blood samples were collected from clinically suspected brucellosis patients (68 men and 84 women) with clinical manifestations of fever, chills, and musculoskeletal pain of less than 8 weeks’ duration. All patients were confirmed for brucellosis using serological assays and PCR. Subsequently, all samples were evaluated for <em>C. burnetii</em> infection using a species-specific PCR assay. Demographic data and potential risk factors were also analyzed. A remarkably high prevalence of <em>C. burnetii</em> infection (76.31%) was detected among brucellosis patients. Livestock exposure was significantly associated with coinfection (p=0.036). Phylogenetic analysis showed close similarity to internationally reported strains. All patients received combination therapy with doxycycline and streptomycin, resulting in clinical improvement. All patients received combination therapy with doxycycline and streptomycin, resulting in clinical improvement. This study provides compelling molecular evidence of a high rate of brucellosis and Q fever coinfection in an endemic region, highlighting a potentially underrecognized public health concern. The findings emphasize the need to consider Q fever in the differential diagnosis of brucellosis, particularly in high-risk populations with livestock exposure. Incorporating doxycycline into empirical treatment regimens represents a rational and effective strategy to ensure adequate coverage against both <em>Brucella</em> spp. and <em>C. burnetii</em> in endemic settings. https://jzd.tabrizu.ac.ir/article_21820_e18eaa635300492859d456a02576bea6.pdf