Chronic Lung Function Decline in Cotton Textile Workers: Roles of Historical and Recent Exposures to Endotoxin

Background: Long-term occupational exposure to cotton dust that contains endotoxin is associated with chronic respiratory symptoms and excessive decline in forced expiratory volume in 1 sec (FEV₁), but the mechanisms of endotoxin-related chronic airflow obstruction remain unclear. Objective: In the current study, we examined temporal aspects of the exposure-response relationship between airborne endotoxin exposure, longitudinal change in FEV₁, and respiratory symptoms in a cohort of Chinese cotton textile workers. Methods: This prospective cohort study followed 447 cotton textile workers from 1981 to 2006. at approximately 5-year intervals. We used a generalized estimating equations approach to model FEV₁ level and respiratory symptoms as a function of past exposure (cumulative exposure up to the start of the most recent 5-year survey interval) and cumulative exposure (within the most recent interval) to endotoxins, after adjusting for other covariates. Models were stratified by active versus retired work status and by years employed before the baseline survey (< 5 and > 5 years). Results and Conclusions: Past exposure to endotoxin was associated with reduced FEV₁ level among retired cotton workers. Among all cotton workers, past exposure was more strongly associated with reduced FEV₁ for those hired < 5 years before baseline than for those who were hired > 5 years after baseline. Recent endotoxin exposure was significantly associated with byssinosis, chronic bronchitis, and chronic cough.