Limitations of WTC Five-Year Assessment
Referencing: The World Trade Center Disaster and the Health of Workers: Five-Year Assessment of a Unique Medical Screening Program
We have learned much about the respiratory disorders since the exposures of responders at the World Trade Center (WTC) site, especially from the publications of Prezant and colleagues about the presentations, follow-up, and impairments of pulmonary function and bronchial reactivity of the fire fighters and emergency medical technicians of the New York City Fire Department (Banauch et al. 2003, 2005, 2006; Prezant et al. 2002). These reports are especially informative because of the availability of preexposure clinical and spirometric data.
We appreciate the report of much-awaited results among 9,442 workers from the WTC Worker and Volunteer Medical Screening Program (Herbert et al. 2006). Because of the potential for major illness, the large number of subjects at risk, and the resultant enormous public interest, it is important that the information reported be properly understood. A number of limitations in this report must be pointed out.
Although the title identified this report (Herbert et al. 2006) as a 5-year assessment, screening examinations were performed between 16 July 2002 and 16 April 2004, < 1 year through < 3 years after 11 September 2001. There were no follow-up examinations, either at the 5-year or at any other interval.
Summary conclusions (Herbert et al. 2006), heavily reported in the media, lump all respiratory symptoms:
. . . 69% reported new or worsened respiratory symptoms while performing WTC work. Symptoms persisted to the time of examination in 59% of these workers.
The 69% with "any respiratory symptom" included 23.3% with no "lower respiratory symptoms." A far smaller percentage of all workers (17.3%) complained of what may be considered the most important respiratory symptom, dyspnea, which was not quantified by any standard scale. Such a reliance on symptoms is subject to recall biases both for symptoms present before 9/11 and for the onset, worsening, and persistence of symptoms after 9/11.
Because physical examination and chest radiographs were unrevealing (Herbert et al. 2006), the only objective results were from pulmonary function tests. These were confined to spirometry, which does not provide insight into all aspects of respiratory impairment. The data presented by Herbert et al. (2006) are limited. Mean values for subsets (classified by WTC exposure, previous smoking history, etc.) are not given. Despite the frequency of cough (42.8%), wheeze (15.1%), and chest tightness (15.4%) and the common diagnoses of asthma/reactive airways dysfunction, only 7.6% of all responders showed airway obstruction, defined as a ratio of forced expiratory volume in 1 sec (FEV1) to forced vital capacity (FVC) less than the 5th percentile of the reference population. Unlike virtually all spirometric surveys of a large population (reviewed by Miller et al. 1991), Herbert et al. (2006) found little difference in impairment by smoking status. Most spirometric impairments were classified as restrictive, uncharacteristic of the symptoms and clinical diagnoses. This frequency of low FVC (22.7%) raises several issues: a) the effects of other clinical factors not reported on, such as obesity; b) technical considerations in subject performance or technician monitoring of the FVC maneuver, despite the investigators attention to these; and c) the appropriateness of the reference-predicted values.
We await further information and follow-up from these investigators, including results of additional diagnostic procedures not included in routine screening. These include a wider array of pulmonary function tests (full lung volumes, diffusing capacity), measurement of bronchial reactivity, computed tomography scans, and—in appropriate patients—bronchoalveolar lavage and lung biopsies, which would truly elucidate the respiratory disorders following WTC exposure.
The author declares he has no competing financial interests.
Albert Miller
Saint Vincent Catholic Medical
Center-Queens
Jamaica, New York
References
Banauch GI, Alleyne D, Sanchez R, Olender K, Cohen HW, Weiden M, et al. 2003. Persistent hyperreactivity and reactive airway dysfunction in firefighters at the World Trade Center. Am J Respir Crit Care Med 168:54–62.
Banauch GI, Dhala A, Alleyne D, Alva R, Santhyadka G, Krasko A, et al. 2005. Bronchial hyperreactivity and other inhalation lung injuries in rescue/recovery workers after World Trade Center collapse. Crit Care Med 33(1 suppl): S102–S106.
Banauch GI, Hall C, Weiden M, Cohen HW, Aldrich TK, Christodoulou V, et al. 2006. Pulmonary function after exposure to the World Trade Center collapse in the New York City Fire Department. Am J Respir Crit Care Med 174: 312–319.
Herbert R, Moline J. Skloot G, Metzger K, Baron S, Luft B, et al. 2006. The World Trade Center disaster and the health of workers: five-year assessment of a unique medical screening program. Environ Health Perspect 114: 1853–1858.
Miller A, Warshaw R, Thornton JC. 1991. Prevalence of spirometric abnormalities in a representative sample of the population of Michigan. Am J Ind Med 19: 473–485.
Prezant DJ, Weiden M, Banauch GI, McGuinness G, Rom WN, Aldrich TK, et al. 2002. Cough and bronchial responsiveness in firefighters at the World Trade Center site. N Engl J Med 347:806–815.
WTC Five-Year Assessment: Herbert et al. Respond
In our article (Herbert et al. 2006), we described the establishment of the World Trade Center (WTC) Worker and Volunteer Medical Screening Program and presented results of screening examinations undertaken between 2002 and 2004 among a heterogeneous group of 9,442 WTC responders.
Miller expresses concern about the validity of self-reported upper and lower respiratory symptoms in WTC responders. He notes correctly that self-reported symptoms are inherently subjective. However, symptoms cannot merely be dismissed as unimportant, especially when they are persistent and when, as was the case here, the pattern of their occurrence closely parallels severity of exposure. We reported that symptoms were most common among those responders who arrived earliest at the WTC site and who consequently suffered the heaviest exposures to the highest levels of dust and smoke (Herbert et al. 2006). This finding has high inherent biological plausibility. To be sure, the potential for recall bias is always present in a symptom-based survey. In reality, however, recall bias could be of concern only if we had reason to believe that responders in different exposure groups recalled past and current symptomatology differently. Finally, to further ensure the validity of our findings, we buttressed our assessment of symptoms with chest X rays and pulmonary function tests.
Miller also expresses concern that objective results were "confined to spirometry, which does not provide insight into all aspects of respiratory impairment." Although we recognize the limitations of spirometry, a large-scale screening program has practical restrictions in testing that can be accomplished. In fact, in Miller's own 1991 survey of a population 10 times smaller than our own (Miller et al. 1991), only spirometry was used as a screening tool. Miller observes that our results were "unlike virtually all spirometric surveys of a large population" since there was "little difference in impairment by smoking status." We would agree with Miller that our population was distinct by the very nature of the exposures involved and that this should be considered in evaluating the lack of difference in impairment based on smoking status. One speculation is that the overwhelming exposure to toxic chemicals at the WTC disaster may have masked differences between smokers and nonsmokers.
Miller erroneously states that most spirometric impairments were classified as "restrictive." We were quite careful not to use this term because it cannot be confirmed by spirometry alone. Instead we chose the designation of low forced vital capacity (FVC) (Herbert et al. 2006). Like Miller, we were surprised by this finding as well as by the observation that fewer responders had reversible airway obstruction, which would have confirmed asthma in those with asthma-like symptoms. However, asthma is by its very nature intermittent, and spirometry tests are only a "snapshot in time," so normal spirometry results do not rule out asthma. Unfortunately, we were unable to provide inhalation challenge tests for the cohort because of the constraints of conducting a large multicenter clinical screening program.
We listed the many possible reasons for a high prevalence of a low FVC in the "Discussion" of our article (Herbert et al. 2006). One member of our working group (G.S.) is currently leading an initiative to estimate the individual contribution of each of these factors by describing the results of additional diagnostic procedures not included in routine screening.
Examinations of the WTC population continue and are expected to proceed for many years to come. As of 31 December 2006, we have examined > 18,500 WTC responders and provided follow-up examinations to > 7,000. We expect to report on findings from those examinations within the next year. In addition, we will be reporting further on the relationship between symptoms and screening spirometry. These analyses should provide further insight into the potential pulmonary impairment of individuals exposed at the WTC disaster.
The authors declare they have no competing financial interests.
Robin Herbert
Gwen Skloot
Kristina Metzger
Philip J. Landrigan
Jacqueline Moline
Diane Stein
Andrew Todd
Stephen M. Levin
Mount Sinai School of Medicine
New York, New York
Sherry Baron
National Institute for Occupational
Safety and Health
Centers for Disease Control and Prevention
Cincinnati, Ohio
Iris Udasin
Environmental and Occupational Health Sciences Institute
University of Medicine and Dentistry
of New Jersey
Piscataway, New Jersey
References
Herbert R, Moline J. Skloot G, Metzger K, Baron S, Luft B, et al. 2006. The World Trade Center disaster and the health of workers: five-year assessment of a unique medical screening program. Environ Health Perspect 114: 1853–1858.
Miller A, Warshaw R, Thornton JC. 1991. Prevalence of spirometry abnormalities in a representative sample of the population of Michigan. Am J Ind Med 19: 473–485.
Erratum
In Table 2 of the the commentary by Marsee et al. [Environ Health Perspect 114:805–809 (2006)], the value for the 75th percentile of monobenzyl phthalate (MBzP) was incorrect; the correct value is 0.92.
The authors regret the error.
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