Chest
Volume 111, Issue 6, June 1997, Pages 1733-1741
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Occupational and Environmental Lung Disease
Accelerated Lung Function Decline in Swine Confinement Workers

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We conducted a longitudinal study to determine the annual rate decline in pulmonary function measurements in male swine confinement workers. For comparison, a grain farming group and a nonfarming rural-dwelling control group were also chosen for the longitudinal study. Two hundred seventeen swine confinement workers, 218 grain farmers, and 179 nonfarming control subjects had valid pulmonary function measurements at the baseline observation conducted in 1990 to 1991 and at the second observation conducted in 1994 to 1995. The swine confinement workers were younger (mean age=38.3±11.7 [SD] years) than the nonfarming control subjects (42.6± 10.4 years) and the grain farmers (44.5±11.9 years). When stratified by age, nonfarming control subjects had the lowest mean annual rate decline in FEV1 and FVC in all age categories. The swine confinement workers had the largest annual rate decline in FEV1 and FVC, and this was most obvious in the middle age categories. After controlling for age, height, smoking, and baseline pulmonary function, swine confinement workers had excess annual decline of 26.1 mL in FEV1 (p=0.0005), 33.5 mL in FVC (p=0.0002), and 42.0 mL/s in forced expiratory flow between 25% and 75% of FVC (FEF25-75%) (p=0.02) over nonfarming control subjects. Grain farmers had excess annual decline of 16.4 mL in FEV1 (p=0.03), 26.7 mL in FVC (p=0.002), and 11.2 mL/s in FEF25-75% (p=0.38) over control subjects. These findings suggest that workers engaged in the swine industry and grain farmers appear prone to accelerated yearly losses in lung function and may therefore be at risk for the future development of chronic airflow limitation.

Section snippets

Materials and Methods

The methods of population selection, data collection, and data analysis for the baseline observations conducted in 1990 and 1991 have been described previously.3, 15 Briefly, all swine operations in the central area of the province of Saskatchewan with annual sales of at least 200 hogs in 1988 were identified from documentation provided by the Saskatchewan Pork Producers Marketing Board. After excluding the swine operations from Hutterite Colonies and swine operations with less than 200 pigs,

Results

As shown in Table 1, the swine confinement workers were significantly younger than the nonfarmers (p<0.001) and the grain farmers (p<0.001). The only significant difference in mean weights was between nonfarming control subjects and grain farmers (p = 0.05). When we examined the follow-up of nonsmokers, current smokers, and former smokers, unavailability of follow-up of smokers was greater in nonfarming control subjects (33/79, 41.8%) than in swine confinement workers (11/41, 26.8%) and grain

Discussion

This is the third study, of which we are aware, in which longitudinal evaluation of swine farmers has taken place following cross-sectional observations. The Ontario cross-sectional study did not find marked differences between swine farmers and dairy farmers,14 but longitudinal observations demonstrated a work association with increased reporting of symptoms on exposure to swine, molds, and grains.17 An early cross-sectional study by Donham et al1 in Iowa did not reveal differences in baseline

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    This study was supported by a grant from the National Health and Research Development Program (NHRDP), Health Canada.

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