Q Fever-Related Community Infections: United States Exposure to Coxiella burnetii

<i>Coxiella burnetii</i> is a significant infectious pathogen that causes Q fever. Q fever is thought to be uncommon in the US and most human cases are believed to occur in agricultural livestock workers. However, the extent of US community exposure to <i>C. burnetii</i> is not known with certainty. Using nationally representative 2003-2004 US National Health and Nutrition Examination Survey serologic, demographic, and occupational history data, the magnitude of US adult general population exposure to <i>C. burnetii</i>, excluding agricultural-sector workers, was estimated. Exposure was defined as positive serum IgG antibodies in an immunofluorescence assay (e.g., current or past infection). A total of 3.0% (95% CI: 2.0-4.4) of the US population met the criteria for <i>C. burnetii</i> exposure, representing some 6.2 million persons. Overall, 86.9% (95% CI: 75.5-98.4) of the seropositive persons had no lifetime history of work in the agricultural sector (5.5 million persons). This was consistently true across all US demographic groups: aged 20-59 years, 87.3%; aged 60+ years, 85.7%; men, 86.1%; women, 87.6%; non-Hispanic Whites, 82%; non-Hispanic Blacks, 95.8%; Mexican Americans, 89.4%; immigrants from Mexico, 83.5%; and other immigrants, 96.8%. As a proportion of <i>C. burnetii</i> infections result in acute Q fever and chronic Q fever conveys significant mortality, the community-level risks to the general public may be significant. It is recommended that a 6-year sample of the most recent NHANES stored sera be analyzed to determine the current community <i>C. burnetii</i> exposure rates. Also, analyzing an additional 2005-2008 stored sera sample would provide an opportunity to assess the time trends and long-term health impacts.