Webber et al. approved by the Institutional Review Board of Montefiore Medical Center. Study participants. The original sample consisted of 14,380 firefighters and EMS workers who were hired before 25 July 2002 (the date the WTC site closed). We excluded 1,636 firefighters who arrived after day 14 or were never present (because of demographic differences between them and earlier arrivals); 369 who did not complete questionnaires; and 1,997 EMS workers (because of differences in their job tasks and because they had less strin- gent preemployment health requirements). The final sample for cross-sectional analysis consisted of 10,378 firefighters. Data sources. We obtained demographics f r o m t h e F D N Y e m p l o y e e d a t a b a s e . Symptoms, exposure status, mask/respirator use, and smoking history were collected from the questionnaires. Symptom prevalence. The questionnaire asked participants about LRS and URS: “Since the disaster, have you had any of the following new or worsening respiratory symptoms?” For LRS, possible answer choices included “no respiratory symptoms,” “wheezing,” “shortness of breath,” and “daily cough”; for URS, possi- ble answers included “no nose or throat symp- toms,” “nasal drip,” “nasal congestion,” “sore throat,” and “hoarse throat with change or loss of voice.” Multiple answers were allowed. We estimated GERD symptoms based on a positive response to “chest tightness or pain” or “stomach upset or heartburn.” Follow-up questionnaires asked participants if they had any of the above symptoms, and affirma- tive answers were qualified as to their pres- ence during “the last 4 weeks.” We obtained information on symptoms pre-9/11 from the participant’s first post-9/11 questionnaire, which asked: “Prior to the disaster did you commonly suffer from any of the following: daily cough, nasal congestion or drip, wheeze, shortness of breath, chest tightness or pain.” Multiple answers were allowed. WTC exposure. The FDNY-WTC expo- sure intensity index (Prezant et al. 2002) categorized exposure based on first arrival at the WTC site as follows: group 1 (the most severely exposed) arrived on the morning of 9/11 and were present during the tower col- lapses; group 2 arrived during the afternoon of 9/11; group 3 arrived on day 2 (12 September 2001); and group 4 (least exposed) arrived on days 3–14. In addition to arrival group, we created two duration variables. The first used infor- mation from questions in which participants reported which months they worked at the site, on or off duty, from September 2001 through July 2002. We used the sum of the number of months participants worked on the site as a continuous variable in multivariate models. We created the second variable, based 976 on both work duration and mask/respirator use, by multiplying each month the partici- pant reported working at the site by 1.0, 0.75, or 0.25, depending on the reported mask/ respirator use frequency of “never,” “rarely,” or “mostly” during that month (Wheeler et al. 2007). The sum of the number of mask-use– weighted months was tested as a continuous variable in multivariate models. Smoking history. “Current smokers” reported smoking cigarettes during any year post-9/11. “Former smokers” reported smok- ing before 9/11 but did not report current smoking in any post-9/11 questionnaire. “Never smokers” consistently reported not smoking pre- and post-9/11. Time periods. In this study we include data from 17,447 questionnaires analyzed cross-sectionally in 1-year periods based on the date administered: year 1, 2 October 2001 to 11 September 2002; year 2, 12 September 2002 to 11 September 2003; year 3, 12 September 2003 to 11 September 2004; and year 4, 12 September 2004 to 11 September 2005. Within each year, if persons completed more than one questionnaire, we used data only from the earliest one. Cohort for analysis of symptom patterns over time. To identify symptom patterns and their relative frequency, we also analyzed a cohort (n = 3,722) that completed question- naires during both the first and fourth years according to four reported symptom patterns: early onset/resolved, early onset/persistent, delayed onset, and asymptomatic initially and at 4 years (Buyantseva et al. 2007). Statistical analyses. Bivariate analyses of categorical variables used the chi-square test with odds ratios (ORs) and 95% confi- dence intervals (95% CIs). We assessed con- tinuous variables using the t-test or analysis of variance. In cross-sectional analyses, we used marginal logistic regression models fit- ted with generalized estimating equations to assess differences in the annual prevalence of symptoms by arrival group, and McNemar’s test for trend to assess the relation of arrival group to symptoms. In the cohort, we tested the linear trend of symptom prevalence over time by arrival group using the Cochran-Armitage test for trend. We used multiple logistic regression analyses with backward elimination to predict outcomes of any LRS, URS, or GERD at fol- low-up. Variables tested in all models included age and years of FDNY service on 9/11, arrival group, duration of work at the WTC site in months and weighted for mask/respirator use, symptoms before 9/11, symptoms reported on initial questionnaire, smoking status (current, former, or never), and elapsed time between initial and follow-up questionnaires. We indi- vidually tested three interaction terms in each model: arrival group and smoking history, arrival group and months of work, and mask/ respirator use and months of work. Variables remained in the model based on a p-value of ≤ 0.05 and assessment of their impact on other variables in the model. Goodness of fit was assessed using the Hosmer-Lemeshow test. Data were analyzed using SAS, version 9.1 (SAS Institute Inc., Cary, NC). Results We collected 17,447 questionnaires from 10,378 WTC-exposed firefighters over the 4-year period from 2 October 2001 to 11 September 2005. During the study, fire- fighter compliance with scheduled periodic evaluations every 18 months, including ques- tionnaire completion, was 85%. Most partici- pants were male (99.8%), were white (93.6%), and never smoked (73.1%). The number of participants in each year of the serial cross- sectional analyses was 8,920 in year 1; 1,197 in year 2; 2,889 in year 3; and 4,441 in year 4. By arrival group, 16.2% (1,683) arrived dur- ing the morning on 9/11, 63.7% (6,611) during the afternoon of 9/11, 11.7% (1,215) on day 2, and 8.4% (869) on days 3–14. The overall mean (± SD) duration of work at the WTC site was 4.4 ± 2.8 months, which dif- fered significantly by arrival group: 4.7 ± 3.0, 4.4 ± 2.8, 3.9 ± 2.5, and 3.3 ± 2.3 months for arrival groups 1–4, respectively (p < 0.0001). Comparing the group of 10,378 with the cohort of 3,722, we found small statistically significant differences in mean age (39.2 years vs. 37.3 years; p < 0.01) and percent Caucasian (93.6% vs. 94.7%; p < 0.01), whereas per- cent male (99.8%) and percent arrival group 1 (16.2%) were the same. Prevalence of symptoms in cross-sectional analyses. Before 9/11, participants had rarely reported LRS: frequent cough was reported by 4.1%, dyspnea by 2.5%, and wheeze by 1.2%. In the first year (2 October 2001 to 11 September 2002), the most common LRS was frequent cough, reported by 54.2%. By year 2, the rate of frequent cough declined to 16.9%, remaining close to that level to affect 15.7% during year 4. In contrast, dyspnea and wheeze showed little change: dyspnea was reported by 40% during year 1 and 38.8% during year 4, and wheeze was reported by 34% throughout all 4 post-9/11 years. Before 9/11, reports of URS were also rare, with frequent sore throat reported by 3.2% and frequent rhinosinusitis by 4.4%. During year 1, the most common respiratory symptom was sore throat, reported by 62.4%. By year 2, the rate of sore throat declined to 36.0%, pla- teauing to affect 37.0% in year 4. In contrast, rhinosinusitis showed little change, varying from 45.1% to 47.8% during years 1 and 4, respectively. Before 9/11, symptoms consistent with GERD were reported by 5.2%. GERD symptoms were reported by 41.8% during ovlume 117 | number 6 | June 2009 • Environmental Health Perspectives