The second cross-sectional study was carried out in three of the four mills originally studied, and a larger mill substituted for the smallest The target population of this study consisted of all 334 employees of the four mills. Personnel records showed that 98 percent were men and 66 percent were black; the mean age was 38.7 years, and the mean length of mill employment was 9.8 years. Thirty-five employees did not work on the day of testing, and four were excluded because they had worked the day before. This left 295 potential participants, and 256 (87 percent) of these were interviewed This group was 97 percent men and 63 percent black, with mean age 38.1 years, and mean length of mill employment 9.9 years. The interviewed employees thus constituted a representative subset of the target population.
Of those interviewed, 52 percent were current cigarette smokers and 20 percent ex-cigarette smokers. Quit smoking cold turkey with My Canadian Pharmacy. Byssinosis was detected in four of 256 (1.6 percent). Mean dust levels were still relatively high, comparable to the levels observed in 1975.
In light of our previous failure to relate average dust concentration to biologic effects, we undertook to define exposure categories by the kind of dust encountered in various areas of the mills. A linter dust category consisted of jobs entailing exposure to cotton dust aerosols. These included seed feeding, cleaning, delinting, hulling, and linter baling. A products dust category included hull sacking, jobs involving the handling of cake, meal and oil, and other jobs remote from linter areas. A mixed category was required for jobs that involved dividing the worker’s time between linter and products areas. In the target population, the distribution of workers in linter, products, and mixed dust categories was 36, 33, and 31 percent In the 256 interviewed, the respective figures were 38, 34, and 28 percent, evidence again of the representative character of the subset. Among these dust categories, the products group workers had the greatest mean age (41.4 years) and length of mill employment (13.0 years). Measured dust levels were not significantly different among these categories.
Allergy skin testing was completed in 230 of the participants. The pride test method was used, and a positive reaction was defined as one at least 2 mm larger than saline control. A battery of ten geographically common inhalants was used to define atopy, which consisted of having two or more positive skin test reactions to these antigens. In addition, two occupational antigens were used: a saline extract of whole cottonseed, and a saline extract of mill dust consisting mainly of cottonseed linters. The overall prevalence of atopy was 15 percent, with similar rates in the three dust exposure categories. Workers in the linter exposure category, however, had excess prevalence of reactivity to whole cottonseed antigen, cottonseed linter antigen, and Fusarium.
Baseline lung function testing showed mean values for FVC and FEVi greater than 100 percent predicted, and a mean FEF25-75 of 87 percent predicted. The means were almost identical among the three dust exposure categories. Declines in expiratory flow rates over the working shift, however, were largest in the linter group. Although there were no significant differences among means, the proportion with FEVX declines exceeding 150 ml was significantly larger in the linter group (31 percent) than in the mixed and product groups (14 and 16 percent, respectively). The acute declines were not significantly related to smoking or dust concentration.
When the three exposure categories were divided into atopic and nonatopic subjects, large declines in FEVi and FEF25-75 were observed only in atopic workers in the linter exposure group (Table 3). This interaction was significant for FEVi at the level P =.05, but fell short of statistical significance for the FEF25-75 (P =.11).
Table 3—Interaction of Atopy and Type of Duet on Acute Declines in Expiratory Flow Rate
|DuetLinter||AtopyStatusAtopic||(n). 9||Postshift Mil Д FEVi, L A -.172||ius Preshift Value FEF25-75, L/sec -.600|