Seroprevalence and risk factors of antibodies against Coxiella burnetii among dog owners in southwestern Québec, Canada

Abstract

Coxiella burnetii is a zoonotic agent responsible for human Q fever, a potentially severe disease that can lead to persistent infection. This cross-sectional study aimed to estimate the seroprevalence to C. burnetii antibodies and its association with potential risk factors in the human population of five regions of Québec, Canada. A serum bank comprising sera from 474 dog owners was screened by an enzyme-linked immunosorbent assay followed by confirmation of positive or equivocal sera by an indirect immunofluorescence assay. Observed seroprevalences of 1.2% (95% confidence interval (CI): 0.0–6.6), 2.6% (95% CI: 0.5–7.4) and 5.9% (95% CI: 3.4–9.6) were estimated in the regions of Montréal, Lanaudière and Montérégie, respectively, which all included at least 83 samples. Having lived or worked on a small ruminant farm (prevalence odds ratio (POR) = 5.4; 95% CI: 1.6–17.7) and being a veterinarian or veterinary student (POR = 6.1; 95% CI: 1.6–24.0) were significantly associated with C. burnetii seropositivity. Antibodies against C. burnetii were detected in the human population of Québec. Although seropositivity to this agent was associated with occupational contact with domestic animals, antibodies were also detected in people with no reported professional exposure. No associations with ruminant farm proximity were identified.

Fig. 1.

Flowchart illustrating the selection of participants, collection of information and results for a C. burnetii seroprevalence study in Québec, Canada, from a source population of 485 potential participants from which sera were available from a 2014 study.

Fig. 2.

Distribution of human sera tested by ELISA for C. burnetii according to their Panbio index values (quantitative results) and their qualitative interpretation with the IFA results for the ELISA-positive sera, ELISA-equivocal sera and ELISA-negative sera with a Panbio index values close to the equivocal threshold. The sera were collected in human participants of Québec, Canada, in 2014 and tested in 2019.

Fig. 3.

Study area, geographical distribution of human participants and distribution of ruminant farm density in 2014 in Québec, Canada, for a C. burnetii serological study. (A) Study area: southwestern portion of the province of Québec, Canada. (B) Geographical distribution of the participants (360) according to their C. burnetii serological status in the five administrative regions studied (qualitatively identified). (C) Geographical distribution of the small ruminant farm density (km²) calculated in ArcGIS using a point density in a 5 km radius around the participants' place of residence. (D) Geographical distribution of the bovine farm density (km²) calculated in ArcGIS using a point density in a 5 km radius around the participants' place of residence.