Pesticide Exposure and Risk of Rheumatoid Arthritis among Licensed Male Pesticide Applicators in the Agricultural Health Study

The occupation of farming has been associated with rheumatoid arthritis (RA); pesticides may account for this association, but there are few studies. We investigated associations between RA and use of pesticides in the Agricultural Health Study. The study sample was drawn from male pesticide applicators enrolled in 1993–1997 who provided questionnaire data at baseline and at least once during follow-up (over a median 18 y; interquartile range 16–19). Incident RA cases ( =220), confirmed by physicians or by self-reported use of disease-modifying antirheumatic drugs, were compared with noncases ( =26,134) who did not report RA. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression, adjusting for enrollment age, state, smoking pack-years, and education. We evaluated the association of RA with the use of 46 pesticides and across 4 levels (never use and tertiles) of lifetime days of use for 16 pesticides with OR≥1.2 for ever use. Incident RA was associated with ever use of fonofos (OR = 1.70; 95% CI: 1.22, 2.37), carbaryl (OR = 1.51; 95% CI: 1.03, 2.23), and chlorimuron ethyl (OR = 1.45; 95% CI: 1.01, 2.07) compared with never use. Statistically significant exposure–response trends in association with RA were observed for lifetime days of use of atrazine [OR = 1.62 (95% CI: 1.09, 2.40); =0.01] and toxaphene [OR = 2.42 (95% CI: 1.03, 5.68); =0.02]. Exposure–response was nonlinear for fonofos [OR = 2.27 (95% CI: 1.44, 3.57); OR = 0.98 (95% CI: 0.54, 1.80); OR = 2.10 (95% CI: 1.32, 3.36); =0.005] and suggestive for carbaryl ( =0.053). Our results provide novel evidence of associations between exposure to some pesticides and RA in male farmers. https://doi.org/10.1289/EHP1013.