The objective of this study was to provide real-world clinical laboratory-based data to supplement Centers for Disease Control and Prevention (CDC) reporting of Q fever. We analysed titre results of specimens submitted to a large US clinical laboratory for Coxiella burnetii IgG antibody testing from 2010 through 2016. Presumptive Q fever was defined as acute (phase II IgG titre ⩾1:128, phase I titre <1:1024) or chronic (phase I IgG titre ⩾1:1024), based on the results from a single serum specimen. During 2010–2016, an average of 328 presumptive acute Q fever cases were identified at Quest each year, nearly three times the annual average reported to the CDC (122). During the same period, the number of chronic cases identified annually at Quest Diagnostics (34) was similar to that reported to the CDC (29). These findings suggest that CDC data may underestimate the incidence of acute Q fever.
