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

## TL;DR

This study estimates that 3% of the U.S. adult population has been exposed to Coxiella burnetii, the bacterium that causes Q fever, with most cases unrelated to agricultural work.

## Contribution

The study provides the first nationally representative estimate of general population exposure to Coxiella burnetii in the U.S., excluding agricultural workers.

## Key findings

- Approximately 6.2 million U.S. adults have been exposed to Coxiella burnetii.
- 86.9% of seropositive individuals had no history of agricultural work.
- Exposure rates were consistent across various demographic groups.

## Abstract

Coxiella burnetii 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 C. burnetii 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 C. burnetii, 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 C. burnetii 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 C. burnetii 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 C. burnetii 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.