The attacks of 9/11 had adverse health impacts far beyond the immediate deaths and injuries from the acute event. The WTC Health Registry, the largest postdisaster registry in U.S. history, is the best opportunity to measure the magnitude of these health problems. Our study estimates that more than 100,000 adults experienced new or worsening respiratory symptoms after 9/11 and that tens of thousands of cases of probable PTSD and thousands of cases of newly diagnosed asthma developed in the first 2 to 3 years after the event. Our findings raise awareness that these adverse health impacts extended beyond workers involved in rescue and recovery to encompass building occupants, residents, passersby, and people in transit in lower Manhattan on 9/11. These findings also underscore the value of the WTCHR as a resource to inform health care services, project needs for affected populations, and link affected individuals to services.
Systematic measurement of 9/11 exposures identified that registry enrollees were heavily exposed to physical and psychological risks, including being caught in the dust cloud, witnessing traumatic events, and sustaining injuries. These exposures correlated strongly with health symptoms. National estimates of expected adult asthma incidence are limited and vary in their range (3-year rates range from 0.8% to 1.6%); all are two to four times lower than the reported asthma incidence among enrollees 2–3 years after 9/11.41–43
Symptoms compatible with PTSD were approximately four times higher than national estimates of current PTSD from disparate trauma sources (16% vs. 4%).44
Among enrollees identified through lists, groups which may have been less subject to self-selection bias, PTSD (12.7%) levels were substantially higher than expected background rates. New diagnosis of asthma in the list-identified group (1.6%) was comparable to the higher end of the national estimate spectrum, but was significantly associated with reported disaster exposures (being caught in the dust cloud, sustaining an injury on 9/11).
To date, the WTCHR has a number of in-depth studies published that examine the health impacts on specific populations (Table ). These studies give additional details on respiratory and mental health findings, as well as more detailed analyses of risk factors and the dose-response association between exposures and health outcomes.12,15,16,21,40
We found that self-reported new diagnosis of asthma was highest among rescue and recovery workers, particularly those working directly on the WTC pile. A previously published WTCHR study of asthma-free workers and volunteers who worked on the WTC site examined the impact of work-related exposures on new diagnosis of asthma and found early arrival time, duration of work on the WTC site, working directly on the pile, and being caught in the initial dust cloud to be independent predictors of developing the condition.12
Other focused studies of rescue and recovery workers have also identified that persons with more intense or prolonged exposure to the WTC collapse and immediate disaster site had more severe respiratory symptoms, conditions, or lung function decline.8–11,45
Summary of previous analysis of health problems using WTCHR
Among lower Manhattan adult residents and office workers, asthma and new or worsening respiratory symptoms were more commonly reported among those who did not evacuate at all and those who returned early, in the first week after the attacks, compared to those who returned later. Few studies have examined exposures and health outcomes in lower Manhattan residents or office workers, but elevated respiratory symptoms have been reported elsewhere.46–49
Few postdisaster studies have addressed new diagnosis of asthma, and no previous disaster is directly comparable to the collapse of the WTC towers on 9/11. Asthma exacerbations have been reported in association with natural disasters, including wild land fires, earthquakes, hurricanes, and volcanic eruptions and wartime exposures to oil fire smoke.50–54
In the occupational setting, some multicase outbreaks have been described, including irritant-induced asthma among police responding to a roadside spill of chemicals used for polymerized plastic coatings, hospital staff following a spill of acetic acid, and those living or working near a spill of metam sodium pesticide.55–57
The prevalence estimates of current, probable PTSD among enrollees 2–3 years after the attacks were higher than those based on self-report from random digit dialed studies in New York City among Manhattan residents conducted 6 to 8 weeks after 9/11 (7.5%), among all New York City adults conducted at 4 and 6 months post-9/11 (2.3 and 1.5%, respectively), as well as national estimates for the general population after 9/11 (4%).20,58–61
Studies done within the first year of other man-made disasters have reported PTSD prevalence in the range of 1% to 11% among the general population and 25–75% among survivors, including a prevalence of 34% among survivors of the Oklahoma City bombing.62–69
In our study, the PTSD prevalence in each WTCHR eligibility group at 2–3 years post-9/11 falls between these ranges reported for the general population and survivors of other disasters. This is likely due, in part, to the fact that lower Manhattan residents, building occupants, passersby, and people in transit as well as rescue and recovery workers experienced both direct and indirect exposures to 9/11. A WTCHR study of rescue and recovery workers found that those at highest risk of PTSD were in occupations least likely to have had prior disaster training or experience, including unaffiliated volunteers (24.7%) and construction or engineering workers (20.8%). Other risk factors included duration of work, earlier arrival, and performing activities uncommon for one’s occupation (Table ).16
Consistent with theories about the causes of PTSD, the prevalence of probable PTSD was higher among enrollees who reported direct exposures on 9/11 indicative of life threat such as sustaining an injury (35%), being caught in the dust cloud (22%), or witnessing a traumatic event (20%). Our findings are consistent with known demographic risk factors for PTSD, including female gender, minority racial/ethnic status, low-income, and middle age in adults.58,61,68,70–76
The relationship between income and PTSD was particularly strong, with persons reporting a household income less than $25,000 having PTSD levels nearly four times as high as those reporting a household income of $150,000 or greater. The other mental health outcome we measured among enrollees was SPD. While less specific in nature, SPD measures psychological distress that is quite severe, usually affecting one’s functionality.24
The prevalence of probable SPD measured among registry enrollees 2–3 years after 9/11 was significantly higher than the citywide prevalence among New York City adult residents during a similar time period (8% compared to 5% in 2003).77
This study has important limitations. The first pertains to the issue of selection bias. Although extensive efforts were made to have a high level of participation in the registry and more than 70,000 persons chose to enroll, the percentage of the estimated eligible persons who enrolled in the registry was low (17.4%), and most enrollees were self-identified. While there were no direct medical, legal, or financial benefits to enrolling in the registry, it is reasonable nonetheless to assume that persons experiencing symptoms were more likely to make the effort to enroll in the registry than those who remained symptom-free. The prevalence of health problems may thus have been overestimated, particularly among the self-identified enrollees. A related potential source of bias is differential enrollment of residents by evacuation status. However, eligible individuals who evacuated after 9/11 would also have been included in the recruitment list building effort, traced intensively in the locating effort by the survey vendor, and exposed potentially to the intensive media and outreach campaigns (e.g., bus, subway, ferry, newspaper, and radio ads).
While the registry is not fully representative, information is available on the population from which the enrolled participants came. Unlike case series studies, the degree of representativeness of registry findings can thus be estimated, and inferences can be made about disease rates; representativeness can be further improved by considering persons recruited from lists, who are less subject to self-selection bias.
A second major limitation pertains to the possibility of recall bias. The registry collected data 2–3 years after the event and relied on self-reported exposure and health information. Enrollees with greater exposure to the disaster may have been more likely to recall symptoms and connect symptoms to the disaster than enrollees with lesser exposure. A related limitation is that timing and severity of symptoms was not collected, and we were unable to distinguish symptoms that resolved immediately or by the time of interview from persistent ones. On the other hand, despite the lack of objective exposure information, we collected detailed information about occupation, location at the time of the event, and duration at high-impact locations that enable the development of proxy measures of exposure to dust or other risks that are less subject to recall bias.
In spite of these limitations, the WTCHR and this study provide a unique perspective on the health effects of the 9/11 disaster. By collecting systematic health information on a wide and diverse group of persons exposed to health risks, it offers among the best estimates of how many people were heavily exposed and the magnitude of adverse health effects. The resultant picture that emerges confirms that the World Trade Center disaster had substantial health implications for large numbers of people, including residents and building occupants who comprise understudied populations post-9/11. Registry data were used to inform the development of physician guidelines and the expansion of 9/11-related services for residents through city-funded programs, including a mental health benefits program and an Environmental Health Center of Excellence described in detail elsewhere (www.nyc.gov/9-11healthinfo
This paper is the first to provide an overview of selected physical and mental health effects on affected adults within the first 2–3 years of the 9/11 attacks and aftermath. More focused studies are needed to fully investigate the relationship between exposures and health problems, and to characterize the severity and duration of the health effects. The World Trade Center Health Registry continues to track enrollees through periodic health surveys, in-depth studies and periodic matches to vital records, cancer registries, and other health data. It will continue to serve as a key resource to study the duration, scope, and severity of health impacts, identify subgroups for more in-depth studies, guide decisions about medical care and other services, and connect individual people to the specific services they need.