Are Farming and Animal Exposure Risk Factors for the Development of Granulomatosis with Polyangiitis? Environmental Risk Factors Revisited.

Objective To investigate the possible association between animal exposure and risk for Granulomatosis with Polyangiitis (GPA). Methods Patients with GPA at the Department of Rheumatology, Uppsala University Hospital, between January 1st, 2011 to December 31st 2018 were consecutively included. All patients filled in a questionnaire on possible environmental exposures; occupation, spare time hobbies and animal contact. As controls we included 128 patients with rheumatoid arthritis (RA) and 248 population controls collected from the EIRA study (Epidemiological Investigation of Rheumatoid Arthritis), matched for age, gender and geographical area of residence. The controls filled out a questionnaire on current and past contact with farming and animals, at the time of the RA patient's diagnosis. Results A total of 62 GPA-patients, 128 RA- and 248 population controls were included in the study. GPA was significantly associated with horse exposure with a two to three-fold increased risk (OR 3.08, 95%CI 1.34-7.08) and 2, 61 (95% CI 1.29-5, 29) respectively. Borderline increased risks were found for any animal contact but no association was found when analyzing contact with cat/dog only. A significant association was found between GPA and farming compared to the population controls OR 7, 60 (95% CI 3, 21-17, 93. Conclusion This study has identified to our knowledge for the first time a significant association between a specific animal exposure, namely horses, and the development of GPA. The results also support previous studies reporting an association between farming and GPA, underscoring the possibility of exogenous factors as initiators in the development of GPA.