A total of 654 (3%) farmers reported a history of doctor-diagnosed chronic bronchitis after age 20 (). Prevalence of chronic bronchitis diagnosis increased with increasing age, BMI, and years on the farm. Current and former smokers were more likely to report chronic bronchitis than never smokers. Those who reported chronic bronchitis were more likely than controls to report a history of other respiratory outcomes, including asthma, emphysema, and wheeze.
General Characteristics of 20,908 Farmers in the Agricultural Health Study by Chronic Bronchitis Status (1993-7)
Pesticide use and pesticide exposure were associated with prevalent chronic bronchitis among AHS farmers (). Farmers who reported having a HPEE in their lifetime were more likely to report chronic bronchitis (OR=1.83, 95% CI= 1.50, 2.24). HPEEs were independently associated with chronic bronchitis and did not modify the odds ratios for the individual pesticides. After adjustment for base-model covariates (age, state, gender, and packyears), 14 insecticides and four herbicides were significantly associated with prevalent chronic bronchitis. Heptachlor, an organochlorine insecticide, had the highest odds ratio (OR=1.71, 95% CI=1.37, 2.13); four other organochlorine insecticides also had elevated odds rations (chlordane, DDT, lindane, toxaphene). Specific organophosphates (coumaphos, diazinon, dichlorvos, malathion, parathion), carbamates (carbaryl and carbofuran), and permethrin were associated with chronic bronchitis. Two chlorophenoxy herbicides (2,4,5-T and 2,4,5-TP) and two other herbicides (chlorimuron-ethyl and petroleum oil) were associated with chronic bronchitis as well. We found no association between chronic bronchitis and any fungicides or fumigants.
Lifetime Pesticide Exposure and the Association With Chronic Bronchitis Among Farmers in the Agricultural Health Study (1993-7)
Use of specific pesticides can be correlated with use of other pesticides. Of the 18 pesticides that were significant in the base model, 11 remained statistically significant after adjusting for the correlated pesticides(). Three pesticides remained unadjusted by other pesticides under our criteria (carbofuran, chlorimuron-ethyl, and petroleum oil); thus, these odds ratios are identical to those in . Heptachlor again had the highest odds ratio (OR=1.50, 95% CI =1.19,1.89). Only DDT remained significant among the other organochlorine pesticides (OR=1.27, 95% CI=1.04,1.56). Three commonly used insecticides (diazinon, malathion, carbaryl) remained significant; although each appeared to attenuate the estimate for the others. The odds ratios for two chemicals commonly used on animals (coumaphos and permethrin) remained elevated (i.e., >1.25) but were no longer statistically significant. The chlorphenoxy herbicides (2,4,5-T and 2,4,5-TP) remained elevated after mutual adjustment.
Pesticides Associated With Chronic Bronchitis Among Farmers in the Agricultural Health Study (1993-7) Adjusted for up to 3 correlated pesticides with correlations >=0.20
presents the dose-response models for the pesticides that remained significant after adjustment for correlated pesticides and the two other pesticides with significant dose-response trends (dichlorvos and permethrin on crops). Despite significant tests of trend, we found little evidence for monotonic increases over all dose levels. Carbaryl, DDT, dichlorvos, malathion, and permethrin on crops all had their highest ORs in their highest lifetime days category. DDT showed a significant dose response trend with risk increasing with increasing number of days of lifetime use. Individuals who used malathion more than 235 days in their lifetime had a 70% increased risk of chronic bronchitis. We saw little evidence that increasing use of herbicides was associated with increased risk of chronic bronchitis, with the potential exception of 2,4,5-TP.
Selected pesticide*-specific dose-response models for Chronic Bronchitis Among Farmers in the Agricultural Health Study (1993-7)
We also evaluated pesticide application activities as risk factors. Using solvents as pesticide additives was associated with chronic bronchitis (OR=1.39, 95% CI =1.07, 1.79). Farmers who applied pesticides to animals were more likely to report chronic bronchitis than those who did not (OR= 1.39, 95% CI=1.18, 1.64). Current farm activities, including crop production, animal handling and production, were not associated with chronic bronchitis, except for handling stored hay (OR= 1.34, 95% CI=1.14, 1.58) and butchering animals (OR= 1.34, 95% CI=1.07, 1.68). We saw no evidence of confounding of the pesticide results by these current farm activities.
A total of 65 percent of farmers (n=13,538) reported holding a job off the farm. Individuals who reported a diagnosis of chronic bronchitis were also more likely than controls to report having had a job off the farm (OR= 1.20, 95% CI= 1.01, 1.43). Odds ratios for off-farm exposures and chronic bronchitis are presented in . Pesticide use off the farm (OR= 1.40, 95% CI= 1.04, 1.88) and solvent use (OR= 1.34, 95% CI= 1.08, 1.66) were significantly associated with chronic bronchitis among farmers.
Off-Farm Exposures and Chronic Bronchitis Among Farmers in the Agricultural Health Study (1993-7)
We saw no evidence of differential effects of these agricultural and occupational exposures among smokers and non-smokers. In models containing a three-level variable for smoking (current, past, and never), we observed no interaction between smoking and pesticide or occupational exposures (data not shown). We had 263 cases of chronic bronchitis among non-smokers (40% of all cases); stratified models suggested similar risk factors for smokers and non-smokers (data not shown).
In models limited to non-asthmatics (499 cases and 19,401 controls), we observed no major differences from the pesticide results for the whole sample. We saw some attenuation of the correlated-pesticide-adjusted results in for heptachlor (from OR=1.50 to OR=1.31, 95% CI=0.99, 1.73), diazinon (from OR=1.25 to OR=1.17, 95% CI=0.92, 1.48), permethrin on crops (from OR=1.26 to OR =1.13, 95%CI=0.86,1.49), permethrin on animals (from OR=1.26 to OR=1.16, 95%CI=0.84,1.59), and 2,4,5-T (from OR=1.31 to OR=1.19, 95%CI=0.92, 1.53). The odds ratios for carbaryl and malathion increased when asthmatics were removed from the sample. We also saw few differences from the dose-response models presented in . The odds ratio for pesticide use off the farm was attenuated from 1.40 to 1.32 (95%CI=0.93,1.87).