Challenges in using serological methods to explore historical transmission risk of Chlamydia psittaci in a workforce with high exposure to equine chlamydiosis

This report describes the challenges encountered in using serological methods to study the historical transmission risk of C. psittaci from horses to humans. Methods: In 2017, serology and risk factor questionnaire data from a group of individuals, whose occupations involved close contact with horses, were collected to assess the seroprevalence of antibodies to C.psittaci and identify risk factors associated with previous exposure. Results: 147 participants were enrolled in the study, provided blood samples, and completed a questionnaire. On ELISA testing, antibodies to the Chlamydia genus were detected in samples from 17 participantsbut further specific species-specific MIF testing did not detect C. psittaci-specific antibodies in any ofthese samples. Conclusion: No serological evidence of past C. psittaci transmission from horses to humans was found in this study cohort. There are major challenges in using serological methods to determine the prevalence of C. psittaci exposure.