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Physical and Mental Health Symptoms Among NYC Transit Workers Seven and One-Half Months After the WTC Attacks
By Loren C. Tapp, MD, MS, Sherry Baron, MD, MPH, Bruce Bernard, MD, MPH, Richard Driscoll, PhD, MPH, Charles Mueller, MS, and Ken Wallingford, MS, CIH American Journal of Industrial Medicine 47:475-483 (2005)
Background
On September 11, 2001, 600-800 New York City transit (NYCT) workers were working near the World Trade Center (WTC) Towers. After the disaster, employees reported physical and mental health symptoms related to the event.
Methods
Two hundred sixty-nine NYC transit employees were surveyed for mental and physical health symptoms 7½ months after the WTC disaster.
Results
Workers in the dust cloud at the time of the WTC collapse had significantly higher risk of persistent lower respiratory (OR¼9.85; 95% CI: 2.24, 58.93) and mucous membrane (OR¼4.91; 95% CI: 1.53, 16.22) symptoms, depressive symptoms (OR¼2.48; 95% CI: 1.12, 5.51), and PTSD symptoms (OR¼2.91; 95% CI: 1.003, 8.16) compared to those not exposed to the dust cloud. Additional WTC exposures and potential confounders were also analyzed.
Conclusions
Clinical follow up for physical and psychological health conditions should be provided for public transportation workers in the event of a catastrophic event.
KEY WORDS: transit workers; terrorist attacks; depression; PTSD; respiratory; mucous membrane
INTRODUCTION
On September 11 2001, approximately 600-800 Metropolitan Transportation Authority, New York City Transit (MTA-NYCT) bus and subway workers were working in areas adjacent to the World Trade Center (WTC) towers. When the WTC towers collapsed, five subway stations and adjoining train tunnels were immediately closed due to structural damage and resulting instability. Buses near the WTC were evacuated and then, in some cases, crushed by falling debris. Transportation services provided by approximately 4,500 buses along 200 bus routes and 700 trains through 470 subway stations stopped for several hours, then resumed to undamaged areas later that day. There were no transit employee fatalities, but approximately 115 injuries were attributable to the collapse, including 49 workers who sustained injuries from contact with chemicals and 40 with smoke inhalation. During the following days, an estimated 2,300 MTA-NYCT workers participated in rescue and recovery activities at Ground Zero and provided transportation services to and from the area.
After the WTC disaster, unions representing the MTANYCTemployees received reports from members concerned about health effects from exposure to airborne substances originating from the collapse of the WTC buildings. Adding to employee concerns were scattered reports of MTA-NYCT employees who had developed symptoms they attributed to the WTC collapse. Several employees reported breathing problems and throat irritation when returning to work after the WTC disaster and some also experienced symptoms suggestive of depression and anxiety. In January 2002, the unions contacted the Centers for Disease Control and Prevention, National Institute for Occupational Safety, and Health (CDC/NIOSH) to request a health hazard evaluation (HHE) to address these health concerns.
In response to this HHE request, NIOSH conducted a study of the MTA-NYCT workers employed in the stations, trains, and buses of NYC to document the extent of physical and mental health symptoms among these workers. This study focuses on employees who began by providing routine transportation services on the morning of the disaster and then were exposed to the physical and psychological trauma of the WTC attacks. We describe the prevalence of mental and physical health symptoms reported by MTA-NYCT workers 7½ months after the WTC disaster and evaluate the relationships between these symptoms and various exposures related to the WTC event. This study was done in parallel with similar NIOSH HHE studies requested by other groups of employees working near the WTC [Bernard et al., 2002].
METHODS
Study Design
This cross-sectional study included MTA-NYCT employees working in various locations in NYC, including the WTC area, the morning of September 11, 2001. WTCrelated exposures and health outcomes were determined by questionnaire responses. This study took place the week of April 30, 2002.
Study Population
The study population included two groups. The first group, defined a priori as exposed, was randomly selected from the roughly 800 full-time MTA-NYCT employees who were working in the subway stations, trains, or bus routes during the hours of 8:30 and 11:00 A.M. on September 11, 2001, and who had worked in or had jobs that required them to pass through the area of Manhattan south of Canal Street. The second group, defined a priori as unexposed, consisted of workers who worked outside of the Lower Manhattan area (North of Canal Street or outside of the borough of Manhattan) in similar work environments (e.g., all station workers worked in underground stations) on September 11th during those same hours. Only workers present at the study sites on the days of the surveys were invited to participate. Due to the logistical challenges of visiting over 100 worksites, those worksites with the greatest number of potential participants were chosen. A joint union/management letter encouraging participation was sent to each eligible worker prior to the survey.
Questionnaire
A self-administered questionnaire was used to obtain information on demographics, past medical history, smoking history, work duties and location, WTC-related activities performed and symptoms occurring on and after September 11th. Participants were asked to complete the survey before or after their shift; those unable to do so were given a stamped, pre-addressed envelope to return the questionnaires directly to CDC/NIOSH. MTA-NYCT management compensated each eligible study participantwho returned a survey, whether completed or not, for 30 min of pay (participation in the study was not required for compensation).
Health outcomes
The Center for Epidemiologic Study-Depression scale (CES-D) [Radloff, 1977] was used to screen for symptoms associated with depression, and the 17 item Veteran's Administration post traumatic stress disorder (PTSD) checklist [Weathers et al., 1993] was used as a screening tool to assess the prevalence of post traumatic stress symptoms (PTSS) among participants. The nature of the WTC disaster and the likelihood that respondents might report a high number of depressive symptoms found on the depression scale led us to raise the score needed to define major depression to 22 or higher out of a possible 60 points on the CES-D, rather than the score generally used as the standard for major depression (16 or higher) [Radloff, 1977; Weissman et al., 1977; Eaton and Kessler, 1981]. Information was obtained on physical symptoms (i.e., upper and lower respiratory irritation, mucous membrane irritation, and gastrointestinal symptoms). Individual symptoms were assessed by a positive or negative response to the question ''Have you had any of the following symptoms after the WTC disaster on 9/11/01?'' Symptom clusters were also assessed. Mucous membrane symptoms were defined as having both eye irritation and nose or throat irritation. Lower respiratory symptoms were defined as having either wheezing or cough without phlegm and either shortness of breath or chest tightness. We defined persistent symptoms as either: symptoms that existed before 9/11/01 but worsened since 9/ 11/01, or new onset symptoms since 9/11/01 that had not improved. ''Persistent mucous membrane irritation'' was defined as having both persistent eye irritation and persistent nose or throat irritation. ''Persistent lower respiratory irritation'' was defined as having either persistent wheezing or persistent cough without phlegm and persistent shortness of breath or persistent chest tightness.
Several indicators of WTC exposure were included in the questionnaire. Workers were classified as ''in the dust cloud'' if they answered yes to either ''I was in a dust cloud so thick I could not see in front of me'' or ''I was in a dust cloud, but it did not prevent me from seeing where I was going.'' Workers ''in the tower zone'' included those who indicated that they were in the area of Manhattan South of 14th Street when the WTC towers collapsed. Workers ''participating in Ground Zero activities'' indicated that they provided paid or volunteer services at Ground Zero during the 7 days following 9/11. These services included search and rescue, food, and transportation, among others.Workers ''knowing a victim'' answered yes to ''Did you know anyone personally who was seriously injured or killed during the WTC disaster?''Workers ''witnessing any events from September 11, 2001'' indicated that they had personally witnessed: the plane(s) crashing into the WTC, the collapse of the WTC tower(s), individuals falling or jumping from WTC windows, bodies or parts of bodies, or pieces of the plane(s).
Confounder variables
Two combination confounder variables were created to take into account an individual's social support networks. ''Perceived support'' expressed the participant's view of supportiveness from family, co-workers, and supervisors (''high'' vs. ''low.'') The amount of ''social contact,'' a continuous variable, was defined by responses to questions concerning the time spent with family members, friends, religious or non-sectarian groups, clubs, and organizations.
Statistical Analysis
When we began the data analysis, we learned that our a priori selection of the exposed and unexposed study groups did not accurately classify study participants with regard to their actual direct exposure to WTC events. To reduce misclassification, we opted to focus analyses on questionnaire responses to specific exposures, disregarding the original group designations. The correlation between being ''in the dust cloud'' and ''in the tower zone'' was moderate (correlation coefficient¼0.58); 83% of those in the dust cloud were also in the tower zone; however, the tower zone encompassed areas with little chance of being in the dust cloud. We chose ''in the dust cloud'' as our major exposure variable for the day of the disaster. We analyzed physical symptoms in relation to two exposure variables (''in the dust cloud'' and ''participating in Ground Zero activities''), and mental health symptoms in relation to four exposure variables (''knowing a victim'' and ''witnessing events on 9/11,'' in addition to the two previously mentioned). Reference groups for each exposure variable included those workers without that specific exposure. Potential confounding factors, such as age, gender, race, Hispanic ethnicity, prior history of physical or mental health diagnoses, and social contact, were taken into consideration where appropriate. Because prior studies have found that those persons diagnosed with depression are more likely to report physical symptoms and seek medical care for reasons other than depression [National Institute of Mental Health, 1999; Stewart, 2003], we also analyzed the physical symptom outcomes considering depressive symptoms as a confounding factor.
To examine the relationships between our outcomes and exposures, we first constructed 2 2 tables and calculated odds ratios (OR) along with their corresponding 95% confidence intervals (95% CI). Where the data were sufficient (i.e., the expected counts of the 2 2 table cells equaled five or greater), we reported OR and 95% CI based on asymptotic results. Exact results were reported where the data may not have been sufficient. Stratified analyses were done to control for extraneous dichotomous risk factors and logistic regression was utilized to adjust for extraneous risk factors of the continuous type. Due to the small number of cases for each of our outcomes, we were limited to controlling for one factor at a time. Results were considered statistically significant when 95% CI excluded one. Statistical software used for the analyses included: SAS version 8.02, SAS Institute, Cary, NC, and StatXact-5, Cytel Software Corporation, Cambridge, MA.
Work Environment Assessment
MTA-NYCT work environments, including subway stations, bus depots, trains, and train yards, were evaluated by NIOSH investigators using qualitative checklists to determine whether environmental factors were similar between the original exposed and comparison worker groups. The checklists included factors such as type of ventilation and occupational exposures to chemical or physical hazards.
RESULTS
Questionnaire
We conducted surveys at approximately 30 subway stations, the Maintenance of Way (MOW) headquarters, 17 train line break rooms, and 5 bus depots. There were 381 MTA-NYCT employees at work at the selected worksites during the scheduled survey times; 27 employees were out due to illness and were not included. Among these 381, 269 (71%) completed the questionnaire (112 refused or did not respond to the survey notification).
Demographics
The average age of participants was 45 years (range 25- 65); 15% were female. Race among participants included 42% Black, 41% White, 3% Asian or Pacific Island descent, 7% other, and 7% chose not to answer. Seventeen percent indicated Hispanic origin. The average number of years worked forMTA-NYCTwas 14; the average number of years worked at the current job was 12. Of the 269 participants, 138 (51%) were train operators or conductors, 79 (29%) were bus operators, and 52 (19%) were Station Workers (26 Station Agents, 5 Station Cleaners, 15 MOW workers, and 6 Structural or Station Maintenance workers). The percentage of study participants in each job type was similar to the percentages in the overall MTA-NYCTworker population. Among participants, 62 (24%) reported being in the dust cloud and 88 (33%) participated in Ground Zero activities. Additional demographic information relating to dust cloud exposure is given in Table I.
Prevalence of Physical Symptoms
Since September 11th Table II lists the prevalence of individual symptoms and defined clusters of symptoms after September 11th and prevalence of persistent symptoms by exposure to the dust cloud. The most prevalent symptoms after September 11th among workers in the dust cloud (in descending order) were eye irritation (67%), cough of any kind (62%), nose/throat irritation (59%), headache (50%), and congestion (45%). The most prevalent persistent symptoms since September 11th among those in the dust cloud (in descending order) were eye irritation (25%), congestion (22%), nose/throat irritation (20%), cough of any kind (20%), headache (18%), and shortness of breath (17%). Of dust cloud-exposed workers having at least one physical symptom, 16 (26%) reported taking time off work due to the symptom(s).
Persistent lower respiratory symptoms by exposure
Workers in the dust cloud had significantly higher risk of persistent lower respiratory symptoms (OR¼9.85; 95% CI: 2.24, 58.93) compared to those not exposed to the dust cloud (Table III). Involvement in Ground Zero activities was not significantly related to increased risk of lower respiratory symptoms (OR¼2.63; 95% CI: 0.64, 11.19). Controlling individually for potential confounders (age, gender, current smoking status, diagnosis of allergies prior to 9/11, and diagnosis of lung disease (asthma, chronic bronchitis, emphysema, or chronic obstructive pulmonary disease) prior to 9/11) did not meaningfully change the relationships between these exposure variables and persistent lower respiratory symptoms. Taking into account depressive symptoms, the associations between persistent lower respiratory symptoms and the exposure variables were also essentially unchanged.
Persistent mucous membrane symptoms by exposure
Workers in the dust cloud and those involved in Ground Zero activities had significantly higher risk of persistent mucous membrane symptoms (OR¼4.91; 95% CI: 1.53, 16.22; and OR¼2.88; 95% CI: 1.03, 8.02, respectively). Controlling individually for potential confounders (age, gender, current smoking status, and diagnosis of allergies prior to 9/11) did not meaningfully change the relationships between the exposure variables and persistent mucous membrane symptoms. The adjusted OR for the associations between persistent mucous membrane symptoms and the exposure variables, taking into account depressive symptoms, were similar to those obtained in the crude analyses.
Prevalence of Depressive Symptoms and Post-Traumatic Stress Syndrome
The number of MTA-NYCT workers who reported witnessing events related to the disaster or knowing a WTC victim were documented. Of the survey participants, 45 (17%) reported witnessing one or both plane(s) crashing into the towers, 28 (10%) witnessed people jumping from the towers, 57 (21%) reported witnessing the collapse of one or both WTC tower(s), 23 (9%) witnessed plane parts amid the debris, 12 (4%) witnessed lifeless bodies or body parts, and 110 (41%) reported knowing aWTC victim. Thirty-one (12 %) of transit workers reported symptoms consistent with major depression and 21 (8%) reported PTSS. Table IV illustrates the prevalence of depressive symptoms and TABLE I. Dust Cloud Exposure and Demographics; Metropolitan Transit Authority NewYork CityTransitWorkers April 2002
Depressive symptoms by exposure
Our analyses found that persons in the dust cloud had significantly higher risk of depressive symptoms (OR¼2.48; 95% CI: 1.12, 5.51) compared to those not in the dust cloud (Table III). We considered the effects of the following variables on the associations between exposure and depressive symptoms: gender, race, Hispanic ethnicity, having been a witness to or victim of a prior traumatic event, amount of social contact,1 job satisfaction, and perceived support from family, supervisors, and coworkers2. Adjustment for these factors resulted in no meaningful differences in the relationship between depressive symptoms and two of the four exposure variables (being in the dust cloud and participating in Ground Zero activities). Differences emerged however for the exposure variables of witnessing the disaster and knowing a victim. When we controlled for reported perceived support, we found a statistically significant association between witnessing the disaster and depressive symptoms (OR¼2.31; 95% CI: 1.04, 5.15). For those subjects that reported being a victim of, or a witness to, a prior traumatic event, the relationships between depressive symptoms and knowing a WTC victim (OR¼3.75; CI: 1.18, 11.94) and between depressive symptoms and witnessing the disaster (OR¼3.94; CI: 1.27, 12.17) were statistically significant.
Post traumatic stress symptoms by exposure
The risk of PTSS was significantly greater among those who reported knowing a victim (OR¼3.07; 95% CI: 1.20,
We evaluated the effects of the following variables on the associations between the exposure variables and PTSS: gender, race, Hispanic ethnicity, having been a victim of or witness to a prior traumatic event, amount of social contact, and perceived support from family, supervisors, and coworkers. Adjustment for these factors resulted in no meaningful differences in the analyses involving being in the dust cloud, participating in Ground Zero activities, and witnessing the disaster. For those subjects that perceived low support from family, coworkers, and supervisors, the association between PTSS and knowing a victim was statistically significant (OR¼16.41; CI: 2.14, 722.96); among those subjects who did not perceive low support there was no association between PTSS and knowing a victim(OR¼0.74; CI: 0.12, 3.66). We found that males had increased risk of PTSS when they were in the dust cloud (OR¼4.07; CI: 1.02, 15.97), but females had no such increase in risk (OR¼0.98; CI: 0.13, 6.29); however, theseOR did not significantly differ for males and females.
Table III shows the OR for each exposure and outcome, controlling for confounders if appropriate.
Prevalence of Health Conditions Newly Diagnosed by a Physician
When comparing MTA-NYCT workers exposed to the dust cloud with those not exposed, six (10%) reported being diagnosed with PTSD after September 11th compared to one (<1%) of those not in the dust cloud, four (7%) were diagnosed with depression or mood disorder compared to two (1%) of unexposed, two (5%) were diagnosed with allergies compared to three (2%) of unexposed, and one (2%) was diagnosed with asthma compared to four (2%) of unexposed. The medical conditions were reportedly diagnosed by a physician and those reporting the conditions as pre-existing (prior to September 11th) were not included.
DISCUSSION
This is the first study to document the extent of physical and mental health symptoms among NYC transportation workers following the WTC disaster. Nearly 3,000 of the 45,000 MTA-NYCT workers had direct exposures to WTC dust, smoke, and fumes, and personally experienced the events of the disaster. Hundreds of MTA-NYCT employees worked in the subway stations and drove the buses and trains that transported people to and from the WTC towers on the morning of September 11th, and over 2,300 participated in search and rescue activities or transported Ground Zero workers to and from the site after the disaster occurred. In addition to the economic burden of search and recovery efforts, rubble removal, the loss of numerous businesses and jobs, and costly clean-up of residential and commercial property, the public health impact of the WTC attacks has been great. Studies of residents and working populations in the WTC area post-9/11 have shown an elevated risk of physical and psychological symptoms resulting from exposures to the WTC collapse [Schuster et al., 2001; Banauch et al., 2002; Bernard et al., 2002; Galea et al., 2002a,b; Levin et al., 2002; Malevskaya et al., 2002; Prezant et al., 2002; Rom et al., 2002; Schlenger et al., 2002; Silver et al., 2002; Trout et al., 2002]. Occupational studies have found significant physical and psychological symptoms in office workers and school staff who were working in the vicinity of theWTC towers [Bernard et al., 2002; Trout et al., 2002]. Medical screening and follow-up of volunteers and workers involved in search and rescue efforts and clean-up at Ground Zero have found physical and psychological conditions related to WTC activities that have persisted upto the current time, some severe enough to prevent return to work [Levin et al., 2002; Prezant et al., 2002]. Our findings are consistent with these prior studies; although the number of persons identified in our survey with physician-diagnosed illness was relatively small, the impact of the WTC attacks was evident.
In this study, persistent physical and psychological symptoms reported by MTA-NYCT workers were significantly associated with WTC-related exposures.MTA-NYCT workers who were directly exposed to the dust cloud had a significant risk of persistent mucous membrane and lower respiratory symptoms and PTSS. The majority of symptomatic workers exposed to the dust cloud had improvement of most of their physical symptoms, but 10%-25% reported that they continued to experience persistent mucous membrane and/or respiratory symptoms 7½ months post-WTC disaster.
The persistent physical symptoms associated with exposure to the dust cloud are likely due to exposure to multiple environmental contaminants (e.g., smoke, respirable airborne particulates, and fire combustion products) from the collapse of the towers and ensuing fires. Environmental air sampling performed days after the collapse of the WTC [Environmental Protection Agency, 2002; McKinney et al., 2002] did not find exposures above established criteria, but because of initial lack of exposure data in the first hours and following days after the collapse, airborne contaminant concentrations, characteristics, and their relationship to resulting health effects remain unclear. Environmental monitoring of undisturbed, settled dust at Ground Zero documented high levels of particulate matter composed of construction material, soot, and glass fiber that was highly alkaline in character (pH>11) [Lioy et al., 2002]. Exposure to these types of particulate would likely account for the symptoms of mucous membrane and respiratory tract irritation. Little is known about the health effects from complex exposures such as occurred as a result of the WTC collapse and subsequent fires. Studies (such as the WTC Worker and Volunteer Medical Screening Program coordinated by Mt. Sinai Center for Occupational and Environmental Medicine) [http://911digitalarchive.org/webcontent/ nycosh/WTCcatasAugNov/Screeningprog.html, accessed March 2005] involving in-depth evaluations and long-term follow-up of first responders, rescue and recovery workers, clean-up workers, and others who worked at Ground Zero should provide useful information for the affected individuals and for those involved with emergency response and preparedness.
We found that 20% of transit workers in the dust cloud had symptoms consistent with major depression and those witnessing the disaster had a greater risk for depressive symptoms. The rate of major depressive disorder (using the American Psychiatric Association's Diagnostic and Statistical Manual [DSM-III] criteria) in the general US population is3%-5%, with transportation worker depression rates falling within this range [Eaton et al., 1990]. Although we used a different diagnostic tool, comparing our findings with these national rates suggests that the prevalence of major depression inMTA-NYCTworkers exposed to the dust cloud was four to five times greater than the rate one would expect to see in a worker population [Eaton and Kessler, 1981]. The CES-D scale we used to identify those with symptoms of major depression may have exaggerated the number of workers with these symptoms since it is used as a 20-question NYC screening tool; a subsequent psychiatric interview (or the highly structured Diagnostic Interview Schedule used in the occupational depression study previously referenced) would eliminate those individuals who do not fulfill the DSM-III (now DSM-IV) criteria for major depressive disorder. In addition, comparing our depressive symptom rates with that study's rates may not be appropriate since those populations had not recently experienced a major disaster.We attempted to balance these discrepancies by using a more stringent CES-D score criterion.
Fifteen percent of NYC transit workers with exposure to the dust cloud had PTSS, and those knowing a victim of 9/11 had a higher risk for PTSS. The prevalence of PTSS among these transit workers was nearly three times greater than that found six months post-September 11th in a national population outside New York City (5.8%) [Silver et al., 2002]; this latter population was categorized by a similar PTSD scale (the Impact of Events Scale-Revised). A study which evaluated survivors 6 months after the bombing of the Federal Building in Oklahoma City found that 34% met the diagnostic criteria for PTSD [North et al., 1999]; these individuals had a greater severity of psychological trauma exposure than the transit workers. Various studies of New York City residents conducted since September 11th have identified elevated prevalence of depressive symptoms and PTSD using a variety of assessment methods [Schuster et al., 2001; Galea et al., 2002a; Schlenger et al., 2002].
Factors other than WTC-related exposures are also important to the mental health of transit workers. Social support influenced how the workers in this study were affected by the psychological trauma of the WTC disaster. Prior studies evaluating psychological symptoms and sick days in subway drivers who experienced a person jumping or falling in front of their train shows conflicting results. One study found that significantly more sick days were reported (associated with a high depression score) from 3 months to 1 year following the event than among those who did not experience such an event [Theorell et al., 1994]; the other found that those with psychological symptoms 1 month postevent had a marked reduction of these symptoms 5 months later [Tranah and Farmer, 1994]. One might expect that these types of traumatic experiences would heighten the psychological impact of a disaster such as the attack and collapse of the WTC; on the other hand, these experiences may serve to blunt some individuals' psychological reaction to other distressing events.
It is difficult to predict the long-term effect from this disaster on mental health. Responses to extraordinary traumatic events may provoke a range of reactions, and symptoms alone are not adequate to fully diagnose medical conditions. Many of the symptoms, which the transit workers experienced, may be normal and reversible reactions to a traumatic event. Researchers evaluating the Oklahoma City bombing found that most individuals directly involved did not develop diagnosable psychiatric illness, but the majority reported experiences such as sleep disturbance, feeling emotionally upset afterwards, and loss of concentration [North et al., 1999]. One additional aspect to consider is that metropolitan transportation workers are a working population that may be more likely to experience a terrorist act (e.g., suicide bombings of Israeli buses, the release of nerve agent (Sarin) in the Tokyo subway) since they are easily accessible, transport the general public, and do not have rigorous security measures, as seen in airports. This could lead to added work-related anxiety. Further systematic investigations using full clinical diagnostic assessment (such as the Mt. Sinai Medical Screening Program), though labor and resource intensive, would be useful in sorting out the breadth and scope of illness in those with persistent symptoms.
Strengths of our study include the well-established measurement tools used to define the psychological outcome variables, the reasonably good participation rate, and the method of defining exposure groups based on reported dust exposure instead of proximity to the WTC area. The major limitation of the study was the potential for recall bias; selfreported data was collected 7½ months after the WTC disaster occurred and remembering circumstances and symptoms close to the time of the event may have been difficult for some. Self-selection bias and reporting bias may have been factors; those in the dust cloud may have been more likely to participate in the study and report symptoms because of early news accounts about the WTC disaster's health effects. Additionally, there is potential for selection bias with regard to the role of social support when selecting worksites with the greatest number of employees, although only train operator and conductor worksites would have been affected.
When developing a response plan for possible future attacks, consideration should be given to public transportation systems and their workers. In the event of a future catastrophe within a metropolitan area, it is critical to include transportation workers in the process of evaluating the public health impact of the event and providing clinical follow up for physical and psychological health conditions. MTANYCT workers providing routine public transportation services who were directly exposed to the WTC disaster events during and shortly after the time of the tower collapses should be included in the medical screening and follow-up programs offered to WTC workers and have access to community-based mental health services.
ACKNOWLEDGMENTS
The authors thank the NYC transit employees who participated in this study, and Doug Trout, Allison Tepper, Toni Alterman, Robert Lambauch, and Bill Eschenbacher for comments on various drafts.
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