BackgroundQ fever is an endemic disease in different parts of Iran. This study aimed to investigate the prevalence of acute Q fever disease among at-risk individuals in northwestern Iran.MethodologyAn etiological study was carried out in 2013 in Tabriz County. A total of 116 individuals who were in contact with livestock and had a nonspecific febrile illness were enrolled in the study. IgG phase II antibodies against Coxiella burnetii were detected using ELISA.Principal findingsThe prevalence of acute Q fever was 13.8% (95% confidence interval [CI]: 8.0, 21.0%). Headache (87.5%) and fatigue and weakness (81.3%) were the dominant clinical characteristics among patients whit acute Q fever. Acute lower respiratory tract infection and chills were poorly associated with acute Q fever. Furthermore, 32% (95% CI: 24, 41%) of participants had a history of previous exposure to Q fever agent (past infection). Consumption of unpasteurized dairy products was a weak risk factor for previous exposure to C. burnetii.ConclusionThis study identified patients with acute Q fever in northwestern of Iran. The evidence from this study and previous studies conducted in different regions of Iran support this fact that Q fever is one of the important endemic zoonotic diseases in Iran and needs due attention by clinical physicians and health care system.