September 11th, 2014 8:56 am ET - Charles B. Hall, PhD
The inhalation of chemicals, particulate matter (dusts and fibers), and the incomplete products of combustion during occupational and environmental disasters has long been associated with respiratory disorders. While there is substantial literature on the association between respiratory diseases and chronic environmental exposures such as air pollution and long term occupational exposure in industries such as mining, silica handling, and construction, much remains to be learned regarding the biological mechanisms that cause such disease and on the latency between acute exposure and disease onset.
The destruction of the World Trade Center (WTC) in New York 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, concrete, and silica; complex organic chemicals; lead; and other metals. Increased incidence of respiratory disease has been reported in firefighters who worked in the rescue/recovery effort and in other cohorts. Obstructive airways diseases (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. New onset OAD continues to be observed many years after exposure, contrary to conventional wisdom that irritant-induced asthma should be triggered within a relatively short time after exposure.
Our research group at the Fire Department of the City of New York (FDNY), one of the Clinical Centers of Excellence in the WTC Health Program, administered by the National Institute for Occupational Safety and Health (NIOSH), used innovative statistical methods to investigate for how long new-onset OAD is associated with WTC-exposure intensity. In this research, funded by a NIOSH cooperative agreement, we assessed whether the higher incidence rates of physician diagnosed OAD seen in FDNY firefighters who experienced a higher intensity of exposure persisted throughout the first five years after September 11, 2001, by allowing the relative rate of new-onset OAD in firefighters with more vs. less exposure intensity to vary over time.
Our results were published in the August 1, 2014, issue of American Journal of Epidemiology. We found that although the relative rate of new-onset OAD diminished after 15 months, it remained elevated in firefighters who had experienced higher exposure intensity for the entire five year follow-up period. Similar results were seen in analyses that examined the incidence of OAD subtypes (asthma and chronic bronchitis). This is a longer period of latency than has been seen in previous studies of short-term exposures, but the WTC-exposure was unusually intense compared to other occupational/environmental exposures.
Our follow-up was limited to five years because in the sixth year of the WTC Health Program, free medications were provided, potentially altering patient-physician behaviors. This made study of incidence rates after year 5 challenging but not impossible as we attempt to determine how much longer the exposure-disease relationship may persist. We also have recently been awarded a new cooperative agreement to examine for how long WTC-exposure-disease relationship persists for new-onset chronic rhinosinusitis. Hopefully, the lessons learned from the study of the health effects of the WTC-responders can contribute to greater protections and better care for the survivors and responders in future disasters.
Charles B. Hall, PhD
Dr. Hall is Professor, Department of Epidemiology and Population Health, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY.
This research was supported by a cooperative agreement from the National Institute for Occupational Safety and Health, grant # U01 OH010412.
For more information on the World Trade Center Health Program visit the webpage.
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