Persistent high IgG phase I antibody levels against Coxiella burnetii among veterinarians compared to patients previously diagnosed with acute Q fever after three years of follow-up.

BACKGROUND

Little is known about the development of chronic Q fever in occupational risk groups. The aim of this study was to perform long-term follow-up of Coxiella burnetii seropositive veterinarians and investigate the course of IgG phase I and phase II antibodies against C. burnetii antigens and to compare this course with that in patients previously diagnosed with acute Q fever.

METHODS

Veterinarians with IgG phase I ≥ 1:256 (immunofluorescence assay) that participated in a previous seroprevalence study were asked to provide a second blood sample three years later. IgG antibody profiles were compared to a group of acute Q fever patients who had IgG phase I ≥ 1:256 twelve months after diagnosis.

RESULTS

IgG phase I was detected in all veterinarians (n = 76) and in 85% of Q fever patients (n = 98) after three years (p<0.001). IgG phase I ≥ 1:1,024, indicating possible chronic Q fever, was found in 36% of veterinarians and 12% of patients (OR 3.95, 95% CI: 1.84-8.49).

CONCLUSIONS

IgG phase I persists among veterinarians presumably because of continuous exposure to C. burnetii during their work. Serological and clinical follow-up of occupationally exposed risk groups should be considered.