The Duration of an Exposure Response Gradient between Incident Obstructive Airways Disease and Work at the World Trade Center Site: 2001-2011
May
The Duration of an Exposure Response Gradient between Incident Obstructive Airways Disease and Work at the World Trade Center Site: 2001-2011
Background: Adverse respiratory effects of World Trade Center (WTC) exposure have been widely documented, but the length of time that exposure remains associated with disease is uncertain. We estimate the incidence of new cases of physiciandiagnosed obstructive airway disease (OAD) as a function of time since 9/11/2001 in WTC-exposed firefighters. Methods: Exposure was categorized by first 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 10 years post-9/11/2001, estimating the time(s) of change in the RR with change point models. We further examined the relationship between self-reported lower respiratory symptoms and physician diagnoses. Results: Change points were observed at 15 and 84 months post-9/11/2001, with relative incidence rates for the high versus low exposure group of 4.02 (95% CI 2.62-6.16) prior to 15 months, 1.90 (95% CI 1.49-2.44) from months 16 to 84, and 1.20 (95% CI 0.92-1.56) thereafter. Incidence in all exposure groups increased after the WTC health program began to offer free coverage of OAD medications in month 63. Self-reported lower respiratory symptoms in the first 15 months had 80.6% sensitivity, but only 35.9% specificity, for eventual OAD diagnoses. Conclusions: New OAD diagnoses are associated with WTC exposure for at least seven years. Some portion of the extended duration of that association may be due to delayed diagnoses. Nevertheless, our results support recognizing OAD among rescue workers as WTC-related even when diagnosed years after exposure.
Background
This research was supported by National Institute of Occupational Safety and Health Cooperative Agreement U01 OH010412.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
The inhalation of chemicals, particulate matter (dusts and fibers), and the incomplete products of combustion during
occupational and environmental disasters have long been associated with respiratory disorders.1 While there is substantial
literature 2,3,4,5,6,7,8,9,10,11 on the association between respiratory diseases and chronic environmental exposures such as air
pollution, and long-term occupational exposure in mining, silica handling, and construction, and other industries, much remains
to be learned regarding the biological mechanisms that cause such disease and the presumed latency period between acute
exposure and disease onset.
The destruction of the World Trade Center (WTC) buildings after a terrorist attack on September 11, 2001, resulted in a
massive, intense dust cloud that was found to contain a huge variety of irritants including partially combusted and/or pulverized
wood, paper, and jet fuel; pulverized construction materials including asbestos, glass, silica, fiberglass, and concrete; complex
organic chemicals; lead; and other metals.12 Increased incidence of respiratory disease has been reported in firefighters who
worked in the rescue/recovery effort and in other worker and non-worker cohorts.13,14,15,16,17 Obstructive airway disease
(OAD), such as asthma and chronic bronchitis, have been shown to be associated with intensity of exposure as measured by
arrival time at the WTC site.18 New-onset OAD continues to be observed many years after WTC exposure,19 contrary to
conventional wisdom that irritant-induced asthma is triggered within a relatively short time after exposure.20 We set out to
determine whether late-onset OAD demonstrated an exposure intensity gradient similar to early-onset disease, which would be
consistent with WTC-causation, or whether the exposure gradient disappears over time.
Methods
Data Sources
Demographic information was obtained from the Fire Department of the City of New York (FDNY) employee database. The
FDNY medical program, run by the FDNY Bureau of Health Services (FDNY-BHS), has used an electronic medical record with
ICD-9 coded diagnoses since 1996. Physician diagnoses for this study were obtained from this electronic medical record. Since
October 2001, FDNY-BHS also has collected data from self-administered health questionnaires completed during routine
monitoring exams conducted every 12-18 months. We used questionnaire information to categorize WTC exposure intensity,
smoking status, and the presence of lower respiratory symptoms of cough, shortness of breath, or wheeze.
Cohort
The study population consisted of uniformed male FDNY firefighters who were on active duty as of 9/11/2001 and had
participated in the WTC rescue/recovery effort on or before 9/24/2001. We excluded those who did not consent for research
(1.6%), those with evidence of pre-9/11 OAD based on FDNY-BHS medical records (5.1%), those who did not have (...truncated)