Objectives The purpose of this study is to determine the trajectory of lung function change after exposure cessation to occupational organic dust exposure, and to identify factors that modify improvement.

Methods The Shanghai Textile Worker Study is a longitudinal study of 447 cotton workers exposed to endotoxin-containing dust and 472 silk workers exposed to non-endotoxin-containing dust. Spirometry was performed at 5-year intervals. Air sampling was performed to estimate individual cumulative exposures. The effect of work cessation on forced expiratory volume in 1 s (FEV₁) was modelled using generalised additive mixed effects models to identify the trajectory of FEV₁ recovery. Linear mixed effects models incorporating interaction terms were used to identify modifiers of FEV₁ recovery. Loss to follow-up was accounted for with inverse probability of censoring weights.

Results 74.2% of the original cohort still alive participated in 2011. Generalised additive mixed models identified a non-linear improvement in FEV₁ for all workers after exposure cessation, with no plateau noted 25 years after retirement. Linear mixed effects models incorporating interaction terms identified prior endotoxin exposure (p=0.01) and male gender (p=0.002) as risk factors for impaired FEV₁ improvement after exposure cessation. After adjusting for gender, smoking delayed the onset of FEV₁ gain but did not affect the overall magnitude of change.

Conclusions Lung function improvement after cessation of exposure to organic dust is sustained. Endotoxin exposure and male gender are risk factors for less FEV₁ improvement.