An Evaluation of Serological Titers for Q Fever in Several Texas Panhandle Populations

Christopher D Bass, The University of Texas School of Public Health


Coxiella burnetii is a gram negative intracellular bacterium associated with the development of Q fever in humans. Enzootic livestock populations can shed large numbers of the bacterium during parturition with resultant human infections occurring through inhalation of contaminated particulate matter and dust. The National Notifiable Disease Surveillance System (NNDSS) received 1,366 confirmed or probable cases of Q-fever between 2000 and 2012 (4). National seroprevalence has been estimated at 3.1% (IFA>1:16) for persons >/= 20 years of age (1). In 2008, a cluster of human Q fever cases possibly associated with a construction site in a Texas Panhandle county resulted in 17(8.5%) workers confirmed positive via indirect immunofluorescence assay (IFA Phase I or II >/=1:128). At the time, the expected human seroprevalence of Coxiella burnetii antibody in the Texas Panhandle was unknown. This questioned whether the construction site incident was indeed an outbreak. It also questioned whether a unique risk factor existed in the Texas Panhandle that contributed to elevated seroprevalence. In 2009, a cross sectional study was designed to determine seroprevalence of Coxiella burnetii within a representative population of Health Service Region One (26 counties of the Northern Texas Panhandle). The study aimed to identify potential risk factors for seropositive persons to include various field exposure activities, agricultural vocations and regional density of concentrated animal feeding operations (CAFOs). Whole blood samples (n=589) obtained from an Amarillo, TX blood bank performing routine site visits were screened for Coxiella burnetii antibody utilizing enzyme-linked immunosorbent assay (ELISA) to phase II antigen with positive or equivocal results confirmed by indirect immunofluorescence assay (IFA>1:128). Results indicated a seroprevalence of 10.7% among the participating blood donors, significantly higher than the 3.1% national estimate determine by Anderson et al (1). Proportion of males (OR - 2.1, 95% CI 1.22-3.73, p<0.01), persons participating in agricultural vocations (OR - 2.7, 95% CI 1.55-4.88, p<0.01) and person’s consuming unpasteurized dairy products (OR-2.0, 95% CI 1.13-3.50, p<0.02) were statistically different between seropositive and seronegative subgroups. Difference in proximity of home residence to nearest CAFO (>200 dairy or beef cattle) was not statistically significant between seropositive and seronegative subgroups, however geo-spatial analysis revealed a distinct south-western distribution of seropositive subject home residences correlating with counties having the highest CAFO counts. This finding may have public health significance and warrants further research: to assess if CAFOs pose risks to public health; and if so, to develop methods of risk reduction through collaboration of the industry, public health officials and scientists.^

Subject Area

Environmental health|Public health|Veterinary science

Recommended Citation

Bass, Christopher D, "An Evaluation of Serological Titers for Q Fever in Several Texas Panhandle Populations" (2017). Texas Medical Center Dissertations (via ProQuest). AAI10617164.