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The New York State Department of Health has conducted a number of studies over the past 10 years investigating health impacts related to the September 11, 2001 (9/11) disaster among New York City residents and New York State World Trade Center (WTC) responders. Efforts to evaluate the health effects of WTC exposures in these cohorts presented numerous challenges, including study design and associated concerns about bias, identifying the affected populations, gaining community support and participation, and determining the most appropriate clinical testing and follow-up approaches. The unique position of a state public health agency provided multiple points of support for these efforts. An overview of what was found and the lessons learned during the response to the 9/11 disaster is presented, from the viewpoint of a state public health agency.
Ten years ago, we began the first investigations of health impacts related to the September 11, 2001 (9/11) disaster among New York City (NYC) residents and New York State (NYS) World Trade Center (WTC) responders. After a substantial effort assessing and following-up their health, we summarize and share what we found and the lessons learned from the 9/11 disaster, from the viewpoint of a state public health agency.
In 2002, the NYS Department of Health (NYSDOH) conducted a retrospective cohort study to assess the respiratory health impacts of 9/11 among NYC residents. Results showed that affected-area residents experienced more lower respiratory symptoms (LRS, 55.8%) and upper respiratory symptoms (URS, 122%) three months post-9/11 compared to control area residents (20.1%).1,2 Both URS and LRS were three times more persistent one year after 9/11 in the affected areas compared to control areas. Follow-up approximately 2–4 years post-9/11, showed declines in LRS but higher proportions of persistent symptoms among affected area residents.3 In a NYSDOH study of NYS WTC responders, URS and LRS were reported by nearly half of participants. One third reported a psychological symptom. Respiratory and PTSD symptoms were associated with being in the dust cloud on 9/11.4 Follow-up studies found WTC exposure was associated with LRS but not with reported asthma two years post-9/11. Smoke exposure may have had a greater lower respiratory impact than resuspended dust.5 Chronic bronchitis was identified as a persistent problem 5-years post- 9/11. Participants with the highest exposures were more likely to experience increased severity of asthma and/or LRS.6 Additional follow-up, 6 years post-9/11, found using a respirator with canister was protective for central airways in responders exposed to dust and smoke.7 Testing of biological samples showed WTC responders were exposed to perfluorochemicals and polychlorinated dibenzofurans.8,9 Comparing residential with occupational exposures, we found new-onset LRS post-9/11 was slightly higher in NYS WTC responders than residents of affected areas.1,2,5 Cough was the predominant LRS among both populations.2,5
We experienced many challenges and developed corresponding strategies in conducting these epidemiologic studies after the WTC disaster. The first problem we encountered was recruitment difficulty because a significant number of residents moved out of the affected area after 9/11 and centralized rosters were not available to track WTC responders. Some individuals refused to answer questions related to the disaster that provoked an emotional reaction, or were overwhelmed with requests for participation from multiple agencies.
Voluntary response could introduce selection bias, i.e., people who experienced symptoms and lived or worked in the affected areas were more likely to participate than those who did not. This bias may have affected the representativeness of our studies and could also have led to overestimation of disease incidence in exposed residents and responders. We minimized this bias by: (1) emphasizing the importance of participation regardless of respiratory issues and using general terms such as “breathing problem”; (2) employing similar recruitment efforts in residential areas or among all WTC responders to reduce differential motivation; (3) using exclusion criteria to limit misclassification due to mobility and occupational exposure; (4) obtaining similar response rates and comparable demographics between exposed and control populations; and (5) estimating the change in exposure-disease association for areas targeted and non-targeted for additional recruitment.
Another important challenge is recall or reporting bias, i.e., affected-area participants or exposed responders might have recalled and reported more symptoms than the controls. To minimize this bias, we asked for specific time frames, severity, and frequency of symptoms, and lists of prescription medications. We also assessed memorable events such as new diagnoses, emergency department visits, and hospitalizations, as they are less prone to recall bias. To estimate reporting bias, we also queried conditions unrelated to WTC and excluded individuals who responded affirmatively to all health conditions. Finally, in some sub-groups, we conducted pulmonary function tests, methacholine challenge tests, and used fractional exhaled nitric oxide (FENO) as a biomarker to validate self-reported symptoms.
Another challenge we faced was a lack of objective exposure measurements. A semi-quantitative exposure assessment was conducted which categorized participants by different patterns of exposure. The algorithm incorporated dust and smoke exposure, time period, and duration on-site, location of work, personal protective equipment used, and quantitative data from air monitoring in pertinent locations.10
The WTC disaster had long-term health impacts for NYC residents and NYS WTC responders. As a state environmental health agency, we had an important role in responding to this tragedy. We developed useful methodologies while evaluating the impacts of this event, learned valuable lessons which may be applied in future natural and manmade disasters, and identified surveillance and research priorities for emergency response.
Conceived and designed the experiments: SL, MPM, EFF, SAH. Analysed the data: RJ, MLH. Wrote the first draft of the manuscript: SL, MPM. Agree with the manuscript results and conclusions: SL, MPM, RJ, MLH, SAH, EFF. Jointly developed the structure and arguments for the paper: SL, MPM, RJ, MLH, SAH, EFF. Made critical revisions and approved final version: SL, MPM, RJ, MLH, SAH, EFF. All authors reviewed and approved of the final manuscript.
Disclosures and Ethics
As a requirement of publication author(s) have provided to the publisher signed confirmation of compliance with legal and ethical obligations including but not limited to the following: authorship and contributorship, conflicts of interest, privacy and confidentiality and (where applicable) protection of human and animal research subjects. The authors have read and confirmed their agreement with the ICMJE authorship and conflict of interest criteria. The authors have also confirmed that this article is unique and not under consideration or published in any other publication, and that they have permission from rights holders to reproduce any copyrighted material. Any disclosures Lessons learned from the 9/11 disaster are made in this section. The external blind peer reviewers report no conflicts of interest.