Exposure to the WTC Disaster and Obstructive Airway Disease
Exposure to the WTC Disaster and Obstructive Airway Disease
There were 962 confirmed cases of OAD during the course of the study, which included 537 cases of asthma and 425 of nonasthma OAD, 417 of which were chronic bronchitis and 8 of which were COPD/emphysema. The median number of FDNY physician visits and the timing of the first visit were nondifferential by exposure group; therefore, they were not included in final models. The only variable that differed by exposure group was OAD incidence (Table 1); differences between exposure groups were significant for any OAD and for both subtypes (likelihood ratios based on Poisson model χ statistics of 53.02, 31.63, and 21.49 for any OAD, asthma, and nonasthma OAD, respectively, all with 2 degrees of freedom, and all P < 0.001).
On the basis of the profile likelihood, the change point from a single change point model was determined to be 15 months after September 11, 2001. A single change point improved model fit over a model without any change points (P < 0.001). Adding a second change point did not improve model fit (P = 0.338); therefore, a 3-change-point model was not considered. Analysis of the linear trend in exposure response found the same change point at 15 months, and that model fit significantly better than the corresponding model with no change points (P < 0.001). We also found no improvement in fit by adding a second change point (P = 0.442) compared with a 1-change-point model.
The relative rates of developing OAD for the most highly exposed group compared with the least exposed group were 3.96 (95% confidence interval (CI): 2.51, 6.26) during the first 15 months after September 11, 2001, and 1.76 (95% CI: 1.26, 2.46) after 15 months (Table 2). These pre– versus post–change point differences were statistically significant both for the high-exposure versus the low-exposure comparison (P = 0.005) and the high-exposure versus the moderate-exposure comparison (P < 0.001). In the final linear trend model, higher WTC exposure level was a significant predictor of OAD, both before (P < 0.001) and after (P = 0.001) the 15-month change point. Sensitivity analyses by OAD subtype showed similar results. The best fitting model for those with asthma was a single change point at 15 months. Before 15 months, the most highly exposed had a relative rate of 4.61 (95% CI: 2.43, 8.73) compared with the least exposed. After 15 months, the relative rate was 1.78 (95% CI: 1.14, 2.79). The 15-month change point model for nonasthma OAD had similar results (Table 2). Although contrasts between high and moderate exposures were nonsignificant both for any OAD and the subtypes, and the contrasts between moderate and low exposures were nonsignificant for the subtypes, the trend tests for asthma and nonasthma OAD were significant both before (P < 0.001) and after (P = 0.013 for asthma; P = 0.030 for nonasthma OAD) the 15-month change point.
More than 88% of the cohort had their first FDNY physician visit for any reason by the 15-month change point, and this rate did not differ significantly by exposure group (P = 0.109). All individuals diagnosed before the 15-month change point reported at least 1 lower respiratory symptom during that period. Of those diagnosed after the 15-month change point (n = 599), 71.8% (n = 430) reported at least 1 lower-respiratory symptom before the change point.
Results
There were 962 confirmed cases of OAD during the course of the study, which included 537 cases of asthma and 425 of nonasthma OAD, 417 of which were chronic bronchitis and 8 of which were COPD/emphysema. The median number of FDNY physician visits and the timing of the first visit were nondifferential by exposure group; therefore, they were not included in final models. The only variable that differed by exposure group was OAD incidence (Table 1); differences between exposure groups were significant for any OAD and for both subtypes (likelihood ratios based on Poisson model χ statistics of 53.02, 31.63, and 21.49 for any OAD, asthma, and nonasthma OAD, respectively, all with 2 degrees of freedom, and all P < 0.001).
On the basis of the profile likelihood, the change point from a single change point model was determined to be 15 months after September 11, 2001. A single change point improved model fit over a model without any change points (P < 0.001). Adding a second change point did not improve model fit (P = 0.338); therefore, a 3-change-point model was not considered. Analysis of the linear trend in exposure response found the same change point at 15 months, and that model fit significantly better than the corresponding model with no change points (P < 0.001). We also found no improvement in fit by adding a second change point (P = 0.442) compared with a 1-change-point model.
The relative rates of developing OAD for the most highly exposed group compared with the least exposed group were 3.96 (95% confidence interval (CI): 2.51, 6.26) during the first 15 months after September 11, 2001, and 1.76 (95% CI: 1.26, 2.46) after 15 months (Table 2). These pre– versus post–change point differences were statistically significant both for the high-exposure versus the low-exposure comparison (P = 0.005) and the high-exposure versus the moderate-exposure comparison (P < 0.001). In the final linear trend model, higher WTC exposure level was a significant predictor of OAD, both before (P < 0.001) and after (P = 0.001) the 15-month change point. Sensitivity analyses by OAD subtype showed similar results. The best fitting model for those with asthma was a single change point at 15 months. Before 15 months, the most highly exposed had a relative rate of 4.61 (95% CI: 2.43, 8.73) compared with the least exposed. After 15 months, the relative rate was 1.78 (95% CI: 1.14, 2.79). The 15-month change point model for nonasthma OAD had similar results (Table 2). Although contrasts between high and moderate exposures were nonsignificant both for any OAD and the subtypes, and the contrasts between moderate and low exposures were nonsignificant for the subtypes, the trend tests for asthma and nonasthma OAD were significant both before (P < 0.001) and after (P = 0.013 for asthma; P = 0.030 for nonasthma OAD) the 15-month change point.
More than 88% of the cohort had their first FDNY physician visit for any reason by the 15-month change point, and this rate did not differ significantly by exposure group (P = 0.109). All individuals diagnosed before the 15-month change point reported at least 1 lower respiratory symptom during that period. Of those diagnosed after the 15-month change point (n = 599), 71.8% (n = 430) reported at least 1 lower-respiratory symptom before the change point.
Source...