Schenker et al. We constructed logistic regression mod- els to assess the association between disease states and variables of interest. Multivariate models always contained age and ever/never smoking status. Odds ratios (ORs) are given with 95% confidence intervals (CIs). We used linear regression models to assess the asso- ciation between continuous independent vari- ables, such as the abundance of carbonaceous substances or crystalline dust, and dependent variables. We used general linear models to determine the association between worker classification and the amount of mineral deposition in lung tissue (least mean squares), with age adjustment. Interaction terms were included in multivariate regression models if the interaction term was significant at the p ≤ 0.05 level and confounders if the OR or the point estimate was altered by ≥ 15%. Table 1. Demographic characteristics of population. Results Study population. All cases were Hispanic males with a mean age of 32.5 years (range, 16–73 years) (Table 1). Approximately one- third had lived in Fresno County ≤ 10 years, one-third for 11‒20 years, and one-third for ≥ 20 years. Overall education was low (mean = 8.1 years), and agricultural workers had significantly less education than nonagri- cultural workers. Approximately half of the subjects were classified as current smokers at the time of death (Table 1). Cause of death was classified according to the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9CM; U.S. Department of Health and Human Services 2002) (Table 2). The predominant causes of death were vehicu- lar accidents (50%), homicide (21%), cardio- vascular disease (10%), and suicide (8%). Values are no. (%) or mean ± SD unless noted otherwise. All subjects were male and Hispanic (total n = 112). aChi-square categorical tests used except for age and years of education, where the Kruskal–Wallis test giving a chi- square value was used. bBased on histologic criteria (see text). Table 3. Global diagnoses based on lung pathology in 112 residents of Fresno County, California, USA. aDefined on histologic criteria as pathologic changes consistent with chronic bronchitis. bDefined on histologic criteria, including the presence of all of the following: smooth muscle hyperplasia/hypertrophy, goblet cell metaplasia, mucous gland enlargement, thickening of basement membrane, and chronic inflammation with lymphocytes and occasional eosinophils. 990 ovlume 117 | number 6 | June 2009 • Environmental Health Perspectives Lung pathology. Gross examination revealed varying amounts of black pigmen- tation in the pleura, around bronchovascu- lar bundles, in the centriacinar zones of the parenchyma, and within hilar lymph nodes. Airway microdissection showed that dust accumulation was less proximally but became distinct around small airways. Grossly recog- nizable emphysema was rarely seen. Many lungs showed parenchymal hemorrhage con- sistent with a traumatic death. Smoking-related small airway disease and mineral dust‒associated small airways dis- ease were seen in 54.5% and 28.6% of all cases, respectively (Table 3). Pneumoconiosis (macules and/or nodules) was observed in 20.9% of subjects, lymph node fibrosis asso- ciated with mineral dust accumulation in 48.7%, pathologic changes consistent with chronic bronchitis in 56.3%, and microscopic emphysema in 23.6%. Asthmalike inflamma- tion and airway wall remodeling were seen in 26.8% of 112 subjects (Table 3). The crude prevalence of mineral dust small airways dis- ease, pneumoconiosis, and pathologic changes consistent with chronic bronchitis was sig- nificantly (p < 0.05) higher among farmwork- ers than among nonagricultural workers and approached statistical significance for lymph node fibrosis and emphysema. In univariate models of the relationship between pathologic disease and mineral dust deposition as evaluated by polarized light microscopy on tissue sections, mineral dust deposition was strongly and significantly asso- ciated with interstitial fibrosis, mineral dust small airway disease, pneumoconiosis, patho- logic changes consistent with chronic bron- chitis, emphysema, and lymph node fibrosis (Table 4). These associations remained signifi- cant after adjustment for age and smoking sta- tus. Cigarette smoking was associated with an OR of < 1 for mineral dust small airways dis- ease, but this association was small compared with the very strong association with mineral dust exposure (OR = 575.4; 95% CI, 39.4 to > 999). Agricultural work was kept in the model for chronic bronchitis over mineral dust because it had a higher point estimate (OR = 2.58; 95% CI, 0.87–7.72), although it did not achieve statistical significance at p < 0.05. Fibrosis of the walls of membranous and respiratory bronchioles was seen in most of the subjects. Examples of airway lesions in the groups are shown in Figure 2. The fibro- sis was significantly (p < 0.05) greater in the upper lobes compared with the lower lobes. Forty-one percent of the nonsmoking, nonag- ricultural workers showed no fibrosis of their respiratory bronchioles (frequency score of 0) (Figure 3). Very few nonagricultural work- ers exhibited a severe grade of airway fibrosis (frequency score > 1.4). Agricultural work- ers had more severe grades of fibrosis. The Characteristic Total no. of subjects (%) Ever smokedb Age (years) Years education Years in Fresno County Agricultural worker 53 (51.5) 32 (60.4) 35 ± 14.2 5.6 ± 3.2 11.9 ± 11.0 Nonagricultural worker 50 (48.5) 26 (52.0) 30 ± 10.5 10.1 ± 2.8 17.2 ± 12.0 Table 2. Cause of death (total n = 112). Cause of death Heart and cardiovascular disease All vehicle accidents Accidental poisonings by analgesics/psychotropic agents Excessive heat Accidental drowning and submersion Agricultural machine accident Accidental electrocution Suicide and self-inflicted injury Homicide and injury inflicted by others Unknown cause aPercentages may not add to 100 because of rounding. Specific feature Mineral dust small airways disease Smoking-related small airways disease Pneumoconiosis (macules and/or nodules) Interstitial fibrosis Lymph node fibrosis Chronic bronchitisa Asthma-like airway diseaseb Emphysema All cases 32 (28.6) 61 (54.5) 23 (20.9) 21 (19.1) 54 (48.7) 63 (56.3) 30 (26.8) 26 (23.6) Overall 103/112 58 (56.3) 32.5 ± 12.8 8.1 ± 3.7 14.95 ± 11.9 410–429 E800–E848 E850–E854 E900 E910 E919 E925 E950–E959 E960–E969 — Significance of difference between agricultural and nonagricultural workersa (9 unknown status) Not significant χ2 = 0.74 p = 0.39 χ2 = 3.18 p = 0.075 χ2 = 35.8 p ≤ 0.0001 χ2 = 5.98 p = 0.0145 12 (10) 54 (50) 5 (4) 1 (1) 4 (4) 1 (1) 1 (1) 9 (8) 23 (21) 2 (2) 0.009 0.392 0.003 0.210 0.072 0.040 0.530 0.073 ICD-9CM code range Frequency (%)a Prevalence (%) Farmworkers 22 (41.5) 32 (60.4) 17 (32.1) 13 (24.5) 30 (56.6) 36 (67.9) 12 (22.6) 17 (32.1) Non-farmworkers p-Value 9 (18.0) 26 (52) 4 (8.3) 7 (14.6) 19 (38.8) 24 (48.0) 14 (28.0) 8 (16.7)