The study uses innovative statistical methods – parametric survival models with change points – to study the incidence of new onset obstructive airway disease (OAD) diagnoses and symptoms over the first ten years following WTC exposure, with the goal of determining the length of time that exposure response gradients are observed among exposed FDNY firefighters. This study will allow estimation of the length of time that a relatively short-term, high intensity exposure may be associated with incident respiratory illness.
Respiratory disorders are associated with occupational/environmental exposures. The latency period between exposure and disease onset remains uncertain. The World Trade Center (WTC) disaster presents a unique opportunity to describe the latency period for obstructive airway disease (OAD) diagnoses. This prospective cohort study of New York City firefighters compared the timing and incidence of physician-diagnosed OAD relative to WTC-exposure. Exposure was categorized by WTC arrival time: high (9/11/2001 AM); moderate (9/11/2001 PM or 9/12/2001); or low (9/13/-24/2001). We modeled relative rates (RR) and 95% confidence intervals (CI) of OAD incidence by exposure over the first 5 years post-9/11/2001, estimating the time(s) of change in the RR with change point models. We observed a change point at 15 months post-9/11/2001. Before 15 months the RR for the high versus low exposure group was 3.96 (95% CI=2.51-6.26) and thereafter, 1.76 (95% CI=1.26-2.46). Incident OAD was associated with WTC-exposure for at least 5 years post-9/11/2001. There were increased rates of new-onset OAD among the high-exposed during the first 15-months and, to a lesser extent, throughout follow-up. This difference in RR by exposure occurred despite full and free access to healthcare for all WTC-exposed firefighters, demonstrating the persistence of WTC-associated OAD risk.
Conventional wisdom has been that new incident obstructive airway disease (OAD) that is associated with environmental or occupational exposure would present weeks to months, not years, after exposure. This research in the FDNY firefighter cohort found that physician diagnosis of incident OAD is associated with World Trade Center (WTC) exposure for at least five years after the exposure. These results support current policy to provide health care for these conditions to exposed rescue/recovery workers regardless of the year of diagnosis, and also adds to the body of evidence that WTC exposure was fundamentally different from previous severe occupational and environmental exposures.
Glaser M, Webber M, Zeig-Owens R, et al. 2014. Estimating the time interval between exposure to the World Trade Center disaster and incident diagnoses of obstructive airway disease. American Journal of Epidemiology. 180(3):272–9.
Hall C, Liu X, Zeig-Owens R, et al. 2015 May. The duration of an exposure response gradient between incident obstructive airways disease and work at the World Trade Center site: 2001–2011. PLoS Currents. 20:7.