Cotton dust and endotoxin exposure and long-term decline in lung function:Results of a longitudinal study

Background: To evaluate the relationship between long-term exposure to cott on dust and Gram-negative bacterial endotoxin on lung function, we conducte d an 11-year follow-up study of cotton textile workers in Shanghai, China. Methods: Workers at a nearby silk-thread manufacturing mill were used as a referent population. Ninety percent of the original cohort of 445 cotton an d 467 silk textile workers both active and retired - were identified for te sting in the 11th year: Questionnaires and spirometric testing were perform ed, as well as cotton dust and endotoxin sampling at three points over the 11-year follow-up period: at baseline, at Year 5, and at Year 11. After exc luding deaths and subjects on sick-leave, 84% of the original cohort had co mplete health and environmental data. Results: The data were reanalyzed using generalized estimating equations fe edback model which allow for subject transfer over time between work areas, various exposure levels to dust and endotoxin, and FEV1. Cotton workers ha d a larger loss of FEV1 during the first 5 years of study (-40 mls/yr) as c ompared with the second 6 years of follow-up (-18 mls/yr). During the same periods, the average decline among silk workers was slightly higher in the first period, but was more consistent (-30 mls/yr vs. -27 mls/yr), and thes e differences could nor be explained by worker selection or dropout. Wizen cumulative exposure to dust and endotoxin were estimated and used in a mult ivariate model (GEE) for FEV1 loss, cumulative dust, but not endotoxin, was associated with 11-year loss im FEV1 after adjustments for confounders. Th ere was evidence of feedback between dust-exposure levels and FEV1, indicat ing the existence of a healthy-worker survivor effect. After accounting for a healthy-worker survivor effect, we found a significant relationship betw een dust exposure and FEV1 decline. Conclusions: Our results suggest that cotton dust is more strongly associat ed with chronic airflow limitation than associated endotoxins. Further work is needed to clarify potential reversibility after cessation of exposure, and the relative contributions of dust, endotoxin, and tobacco to chronic r espiratory impairment in cotton and other vegetable-exposed workers. Am. J. Ind. Med. 35:321-331, 1999. (C) 1999 Wiley-Liss, Inc.