The Sixteenth Conference of the International Society for Environmental Epidemiology (ISEE): Abstracts
Several epidemiologic studies have reported increased risk of rheumatoid arthritis (RA) among farmers. However, the exposures accounting for any increase (e.g., pesticides, silica, solvents) have not been extensively investigated. We studied farming activities and exposures as risk factors for RA among women in the Agricultural Health Study (AHS), a cohort of licensed pesticide applicators and their spouses. We attempted to validate diagnoses for 430 women who self-reported that they had RA in the 5-year followup interview. RA diagnosis was confirmed for 140 women (33%) through a combination of self-confirmation upon callback and contact with physicians. Among the remaining women, 29% did not confirm the diagnosis themselves when recontacted, 28% were not confirmed by the physician, and 10% were never reached. Among the 140 ′confirmed’ cases, RA diagnosis was considered confirmed in several ways. A woman was classified as having ’physician-confirmed RA’ if any one of her physicians indicated that she had a diagnosis of RA, or indicated that she satisfied 4 of 7 American Rheumatism Association (ARA) criteria for RA diagnosis. In addition, ′self-confirmed RA’ was classified as self-confirmation of RA diagnosis upon re-interview in the validation effort and return of a signed form consenting physician contact, regardless of whether any physician responded. Five controls for each case were selected from all women in the AHS cohort, matched on birthdate (n=700). Longterm smoking was associated with 80% increased risk for more than 20 pack-years (OR=1.8, 95% CI: 1.0-3.4), consistent with previous reports. The risk of RA was not associated with having ever personally mixed or applied pesticides (of any type), nor did it vary by the number of days or years a woman participated in this activity. However, certain insecticides were associated with increased risk, including organochlorines (OR=1.6; 95% CI: 0.9-2.8) such as DDT (OR=1.5, 95% CI: 0.7-2.9) and lindane (OR=3.7, 95% CI: 1.3-10.9), and organophosphates (OR=1.3, 95% CI: 0.9-1.9) such as malathion (OR=1.4, 95% CI: 0.9-2.1) and DDVP (OR=1.9, 95% CI: 0.8-4.6). Welding on the farm or in another job was associated with increased risk of RA (OR=2.7, 95% CI: 1.1-6.5). These reported associations were generally present in each state, and upon restriction to cases whose diagnosis date was confirmed to follow exposure. Other farming exposures, including herbicides and solvents, were not associated with RA, nor were residential pesticide applications. Because of the severe disability associated with this relatively common disease, further investigation into causes is warranted.