Objectives Whether cessation of exposure to endotoxin containing organic dusts leads to transient vs. sustained improvement of lung function is unknown.
Method The Shanghai Textile Workers study is a 30-year prospective cohort study of 447 cotton workers exposed to endotoxin containing cotton dust and 472 control silk workers unexposed to endotoxin. Spirometry and questionnaires were administered at 5 year intervals, and endotoxin sampling was performed to estimate individual cumulative exposures. The effect of work cessation on FEV1 was modelled with a generalised additive mixed effects (GAMM) model.
Results When cessation was modelled as a smoothed term, adjusting for age, gender, height, and smoking history, cessation was associated with a significant FEV1 improvement in both cotton and silk workers. Work cessation displayed a non-linear quadratic effect on FEV1, with an average adjusted +38.1, +220, +316 ml effect in silk and +26.3, +184.1, +264.1 ml effect in cotton workers at 10, 20, and 25 years of work cessation. In a model allowing for a quadratic effect of cessation years as suggested by the GAMM model, the linear component of the interaction suggested that cessation of cotton work was associated with less FEV1 improvement than silk work (cotton*cessation year interaction ß = -2.6 ml, p = 0.025).
Conclusions Lung function improvement after work cessation was observed in both cotton and silk workers, suggesting that non-endotoxin containing organic dust exposure has adverse respiratory effects. The greater improvement in FEV1 in silk compared to cotton textile workers suggests that the endotoxin component of cotton dust is associated with additional detrimental effects.