Lung function and farm size predict healthy worker effect in swine farmers.

Background: Swine farmers are exposed to a number of airborne contaminants associated with respiratory ill health.

Objectives: To examine the factors associated with healthy worker effect in the swine industry from a longitudinal follow-up of farmers at 4 years and 13 years.

Design: A prospective study of swine farmers and nonexposed rural residents was conducted using similar questionnaires and same spirometer at each time point.

Results: In the original observations in 1990/1991, we studied 302 swine farmers and 261 nonfarming control subjects. Four years later in 1994/1995, 217 swine farmers and 171 nonfarming control subjects of the original group participated again. In 2003/2004, 163 swine farmers and 118 control subjects were retested. Of the 163 swine farmers, 52 remained active swine farmers and 111 were no longer swine farming, thus providing the opportunity to evaluate work continuity in the industry. Among farmers studied in 2003/2004, mean values for percentage of predicted FEV(1)/FVC ratio and forced expiratory flow between 25% and 75% of FVC were lower in those who had quit swine farming compared to those still swine farming and nonfarming control subjects. The herd size in the barn at baseline in 1990/1991 and at interim follow-up in 1994/1995 was a significant predictor of quitting swine farming. In addition, percentage of predicted FEV(1)/FVC at the interim observation was a significant predictor of quitting swine farming.

Conclusions: There is a significant healthy worker effect among swine farmers. The continuation of work in the facilities may be predicted by herd size and interim lung function.