What are the pitfalls? Although the evidence for shift changes predicting longitudinal decline in exposed swine confinement workers is reasonable, it is not certain whether the same substances in the complex environmental exposure inside swine confinement buildings are responsible for both the acute process (as observed by shift changes) and chronic change (as observed by annual decline), although endotoxins appear important. Second, the methodology of obtaining the follow-up evaluations in 1994/95 was different than that of 1989/90, in that the first observations were obtained on-site in the swine facilities, while the follow-up observations were obtained in a nearby town or village, which required a period of absence from exposure (estimated at between 1 and 2 h).However, this circumstance would likely mitigate toward an underestimation of the annual rate change because the FEV 1 and FVC measurements conducted on the first occasion onsite might be more likely to include acute changes as a result of exposure at the time.

Third, there was only minimal correlation between the 1989/90 and the 1994/95 environmental measurements. This minimal correlation could be due to changes in management practices over the study period that may cause variability in environmental conditions. Changes to manure handing procedures, feed types, cleaning methods and ventilation systems can afect the levels of contamination. Because no relationship was seen with the 1989/90 environmental data, further investigtion of the association between environment and changes in lung function is required to elucidate the role of changes in facility management.

Taken together, our interpretation of the evidence is that shift-change measurements in FEV 1 and FVC are reasonable predictors of longitudinal decline in exposed swine workers and can be conducted with sufficient reproducibility to assess the effectiveness of environmental control or personal protection in these facilities.