Several limitations of the study should be recognized, mainly related to the size of the cohort, the follow-up time period, and the suboptimal spirometry. The size of the inception cohort was constrained by the company’s production plans and an automated manufacturing process. As noted above, the 1-year follow-up duration limits insight into the prevalence of TDI sensitization and asthma, which can take longer than 1 year to develop, and almost 25% of the initial inception cohort was lost to follow-up. The reason(s) workers had resigned from the company or refused to participate was not available. Efforts are on-going to follow- up these workers. Further medical evaluation of workers with findings suggestive of possible isocyanate asthma could help clarify risk, but was not feasible. Unfortunately baseline spirometry was obtained on less than half of the workers and at a different facility, and the full spirometry data was not available, limiting quality assessment and analysis. These considerations were taken into account in interpreting the findings.