American Journal of Epidemiology Advance Access published July 21, 2009
American Journal of Epidemiology
ª The Author 2009. Published by the Johns Hopkins Bloomberg School of Public Health.
All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.
DOI: 10.1093/aje/kwp165
Original Contribution
Lack of Association Between Estimated World Trade Center Plume Intensity and
Respiratory Symptoms Among New York City Residents Outside of Lower
Manhattan
Robert J. Laumbach, Gerald Harris, Howard M. Kipen, Panos Georgopoulos, Pamela Shade, Sastry
S. Isukapalli, Sandro Galea, David Vlahov, and Daniel Wartenberg
Initially submitted December 15, 2008; accepted for publication May 15, 2009.
Researchers have reported adverse health effects among rescue/recovery workers and people living near the
World Trade Center on September 11, 2001. The authors investigated the occurrence of respiratory symptoms
among persons living outside of Lower Manhattan in areas affected by the World Trade Center particulate matter
plume. Using a novel atmospheric dispersion model, they estimated relative cumulative plume intensity in areas
surrounding the World Trade Center site over a 5-day period following the collapse of the buildings. Using data from
a telephone survey of residents (n ¼ 2,755) conducted approximately 6 months after the event, the authors
evaluated associations between the estimated plume intensities at individual residence locations and self-reported
respiratory symptoms among nonasthmatics, as well as symptoms and nonroutine care among asthmatics. Comparing persons at or above the 75th percentile of cumulative plume intensity with those below it, there was no
statistically significant difference in self-reported new-onset wheezing/cough after September 11 (16.1% vs.
13.3%; adjusted odds ratio ¼ 1.0, 95% confidence interval: 0.7, 1.7) and no worsening of asthma from before
September 11 to the 4 weeks prior to the survey (13.9% vs. 16.6%; odds ratio ¼ 1.0, 95% confidence interval: 0.3,
2.8). These results suggest that the plume was not strongly associated with respiratory symptoms outside of Lower
Manhattan, within the limitations of this retrospective study.
air pollution; asthma; inhalation exposure; New York City; particulate matter; respiratory tract diseases; September
11 terrorist attacks
Abbreviations: CI, confidence interval; WTC, World Trade Center.
September 14, rain washed out most of the remaining
particles.
In this study, we assessed a possible association with
increased respiratory symptoms among persons living outside of Lower Manhattan who were exposed to the WTC
plume. We used results from a simulated plume intensity
model to estimate individual residential exposures, because no measurements of ambient air quality were taken
in the vicinity of Ground Zero in the days immediately
following 9/11. Particulate matter concentrations at several
other Lower Manhattan sites were elevated above normal
background levels, but these sites were not located directly
Dust and smoke created by the destruction of the World
Trade Center (WTC) in New York City on September 11,
2001 (9/11) initially engulfed the site and its vicinity in
Lower Manhattan. While the impact was most graphic and
intense at ‘‘Ground Zero,’’ aerial photographs and other
observations demonstrated that airborne emissions extended well beyond the immediate vicinity of Ground
Zero. Over several days following the event, the plume
of air contaminants spread to parts of Brooklyn and New
Jersey, as well as other areas in Manhattan, shifting with
changing wind direction and eventually extending into
Westchester and areas farther away on Long Island. On
Correspondence to Dr. Robert Laumbach, Environmental and Occupational Medicine, University of Medicine and Dentistry of New Jersey–
Robert Wood Johnson Medical School, 170 Frelinghuysen Road, Piscataway, NJ 08854 (e-mail: laumbach@eohsi.rutgers.edu).
1
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Laumbach et al.
in the path of the plume (1). In the absence of direct measurements, previous investigators developed a novel atmospheric dispersion model that combined numerical
modeling and ground- and space-based observations to
reconstruct the path and intensity of the plume from the
WTC site (2–4). In the present study, we used this model to
estimate relative plume intensities in locations throughout
the region.
Health effects from exposure to dust and other emissions
from the WTC site have been demonstrated most readily
among firefighters and other rescue and recovery workers,
who probably had the highest exposures. For example, firefighters exhibited increased coughing with bronchial hyperreactivity (5, 6), as well as sarcoid-like pulmonary disease
(7). Other WTC responders exhibited increased respiratory
symptoms and abnormal pulmonary function (8).
New York City residents exposed to the plume, most of
whom had substantially lower exposures than the rescue
workers, have not been studied in as much detail as the
rescue and recovery workers. In a survey of Manhattan
residents living south of 110th Street, 27% of 134 respondents previously diagnosed with asthma reported worsening
of symptoms since 9/11 (9). A review of charts of 205
pediatric asthma patients at a Lower Manhattan clinic
found that numbers of clinic visits and medication prescriptions were greater during the year following 9/11 than
during the year before 9/11 (10). A survey of enrollees
in a managed-care plan found that residence in Lower
Manhattan or western Brooklyn was associated with selfreported worsening asthma after 9/11 (11). Similarly, nonasthmatic residents of buildings close to Ground Zero
reported statistically significantly more new-onset and
persistent new-onset respiratory symptoms than residents
of buildings several miles away in Upper Manhattan
(12, 13). However, these studies had significant limitations,
including lack of an objective measure of exposure to the
WTC plume and a low participation rate in the latter
2 studies.
In this study, to evaluate the impact of the WTC plume on
residents living outside of Lower Manhattan, we used data
from a representative population sample surveyed by telephone and modeled estimates of WTC plume intensity by
space and time. We assessed whether measures of estimated
plume intensity in neighborhoods of respondents were associated with new-onset and worsening respiratory symptoms among subjects with and without previous diagnoses
of asthma.
MATERIALS AND METHODS
Study population
Our study subjects were respondents to a random digit
dialing household survey of self-reported respiratory
symptoms and related health-care utilization conducted
between March 25 and June 25, 2002, approximately
6 months after the WTC disaster. Sampling and collection
methods have been described elsewhere (14, 15). The sampling frame included all adults residing in the New York
City metropolitan area on 9/11, from which equal numbers
of people were sampled from 4 geographic zones radiating
out from the WTC site. A total of 2,755 persons were
interviewed. The overall cooperation rate was 56%. To
address concerns about likely biases associated with close
proximity of residence to Ground Zero (discussed below),
we excluded residents of Manhattan south of 14th Street
(about 3 km north of Ground Zero), the area defined in the
survey as closest to the WTC, from most of our analyses.
Additionally, we excluded 33 subjects who reported being
involved at the WTC site as emergency, construction, or
health-care personnel, thus retaining 1,810 out of 2,755
persons.
Survey methods
All interviews were conducted by trained interviewers,
who used a computer-assisted telephone interview system
and a structured questionnaire. Interviews were available in
English, Spanish, and Chinese. The institutional review
boards of the New York Academy of Medicine and the
University of Medicine and Dentistry of New Jersey reviewed and approved the study, and all study subjects provided verbal consent at the time of the interview.
We used a series of questions to assess respiratory symptoms prior to 9/11 and prior to the survey (15). Subjects
were classified as asthmatic if they responded ‘‘yes’’ to the
question, ‘‘Has a doctor ever told you that you have
asthma?’’ Subjects who denied a diagnosis of asthma prior
to 9/11 were considered to have new-onset respiratory
symptoms if they answered ‘‘yes’’ to the following
questions: ‘‘In the past 12 months, have you had wheezing
or whistling in the chest or have you been bothered by
coughing, apart from a cold or respiratory infection?’’
and ‘‘Did the problem start after September 11, 2001?’’
Consistent with the approach of Reibman et al. (13),
new-onset respiratory symptoms were considered to be
persistent if the subject’s answer was 8 or more in response
to the question, ‘‘In the past 4 weeks (28 days), how many
days did you have this problem?’’ Subjects who reported
having received a physician’s diagnosis of asthma prior to
9/11 were also asked how they would describe their asthma
(1 ¼ no symptoms, 2 ¼ mild, 3 ¼ moderate, 4 ¼ severe).
Worsening of asthma symptoms was defined as having
moderate-to-severe symptoms during the 4 weeks prior
to the survey as compared with having no symptoms or
mild symptoms during the 4 works before 9/11, consistent
with the definition of Fagan et al. (9). Subjects with asthma
were classified as needing nonroutine medical care for
asthma since 9/11 if they answered ‘‘yes’’ to any portion
of a 3-part question: ‘‘Since the WTC disaster: 1) have you
gone to a hospital emergency room for asthma symptoms?;
2) have you had to stay overnight in the hospital due to
your asthma?; 3) have you had to make an unscheduled
visit to a doctor or health-care provider for your asthma?’’
Additionally, subjects were asked whether they had experienced ‘‘difficulty breathing because of smoke and debris
during the event.’’ We also elicited information about sociodemographic characteristics (age, sex, race/ethnicity,
annual household income, education, marital status, and
smoking).
WTC Plume Intensity and Respiratory Symptoms
3
Cumulative plume intensity estimates
To obtain relative potential exposure intensities for this
study, we simulated the plume generated by the collapse of
the WTC buildings and the subsequent fires at the site. We
used the Regional Atmospheric Modeling System/Hybrid
Particle and Concentration Transport model to reconstruct
the atmospheric dispersion of ‘‘generic’’ particulate matter
on the basis of a triple-nested modeling domain of 4- 3
4-km (grid 1), 1- 3 1-km (grid 2), and 250- 3 250-m (grid
3) resolutions, all centered at the WTC. Details on the
plume reconstruction have been presented elsewhere (3).
The results for the ground layer ranging from 0 m to 20 m
in height were averaged to produce 8-hour particulate
matter concentrations for the geographic areas included
in the household telephone survey and incorporated
a source decay factor that matched the observed plume
intensity. This decay factor was empirical and was used
to account for the decrease in the intensity of the fires and
other emission sources during the days after 9/11. Because
most remaining dust was settled and/or washed away by
rain on September 14, which also diminished the intensity
of the fires and the associated plume, we used the sum
of the first 15 8-hour periods (120 hours total) following
9:00 a.m. on 9/11 as the cumulative plume intensity estimate for our analyses. These intensity estimates were
calculated for each grid cell in the modeling study area.
Although fires continued to burn for many days afterwards,
their contribution to the estimated cumulative plume intensity was negligible, as observed from aerial images
of the plume.
Cumulative residential plume intensity estimates were assigned to telephone survey participants on the basis of address
for persons who lived in New York City on September 11,
2001. The assigned plume intensity was based on the value of
the grid cell that covered the residence location. Respondents
who lived outside of New York City on that date were assigned a plume intensity estimate corresponding to the center
of the town they lived in. The 5-day cumulative relative plume
intensity at the location of residence was used as a proxy for
exposure, since no time-activity data were available for survey
participants.
Figure 1 shows the cumulative distribution of individually
assigned plume intensities. We focused on residents living
outside of Lower Manhattan and classified subjects as exposed if their plume intensity was greater than or equal to
the 75th percentile of the distribution. The cutpoint at the
upper quartile was an arbitrary, a priori selection given that
plume intensity estimates were based on a relative scale.
Sensitivity analyses showed essentially similar results at
higher and lower cutpoints.
Statistical methods
To characterize the study population, we cross-tabulated
exposure status with the demographic variables (age, sex,
education, race/ethnicity, smoking status in the last 12
months, and total combined household income in the last
year before the survey) for subjects living outside of Lower
Manhattan. We assessed the comparability of the exposed
Figure 1. Cumulative probability of the estimated intensity of particulate matter concentrations in the World Trade Center plume over
New York City following the September 11, 2001, attack, by geographic area. Cumulative probability for plume strength (estimated
cumulative plume intensity) at survey participants’ residential locations in the 3 regions was used in analyses of associations between
plume intensity and respiratory symptom outcomes. Plume strength is
expressed in relative, dimensionless units.
(at or above 75th percentile) and unexposed (below 75th
percentile) populations by comparing their sociodemographic and behavioral data using Wald’s v2 test. Given that
persons with a self-reported previous diagnosis of asthma
were likely to respond differently to the plume than persons
without that diagnosis, we conducted separate analyses for
these groups.
We used logistic regression to quantify the strength of the
associations between plume intensity and new-onset wheezing/coughing and persistent new-onset wheezing/coughing
in nonasthmatics and worsening of asthma symptoms in
asthmatics. Odds ratios and 95% confidence intervals are
reported. These models included adjustment for age, sex,
education, race/ethnicity, smoking status, marital status,
and income. All analyses were performed on weighted
data, except for reporting the raw count data. Weights were
selected to account for oversampling and possible sample
selection biases (see Galea et al. (14)). SAS software (SAS
Institute Inc., Cary, North Carolina) was used for all
analyses.
RESULTS
Demographic factors
Demographic data for survey respondents, excluding
those living in Lower Manhattan, are presented in Table 1.
Among nonasthmatics, the exposed were more likely than
the unexposed to report difficulty breathing because of
smoke and debris during the event, tended to have lower
incomes, and were more likely to be college graduates.
Among residents in these areas who reported a previous diagnosis of asthma, we found a statistically significant difference in smoking status, with nonsmokers being much
more likely to be exposed than smokers.
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Laumbach et al.
Table 1. Demographic Characteristics of Survey Participants Residing in Areas Near the Site of the World Trade
Center Collapse on September 11, 2001, by Exposure Statusa and Asthma Status, Spring 2002
Nonasthmatics
Exposed, %
(n 5 434)
Unexposed, %
(n 5 1,170)
<34
39.8
35–54
55
Asthmatics
Exposed, %
(n 5 69)
Unexposed, %
(n 5 169)
37.3
38.7
46.0
37.6
40.1
36.7
35.5
22.6
22.6
24.5
18.4
Male
46.0
47.3
28.9
38.6
Female
54.0
52.7
71.1
61.4
Age, years
x
P
Value
2
0.68
Sex
0.15
Education
3.80
0.71
0.70
0.05
Less than college
graduation
63.5
57.1
56.5
61.1
College graduation
or more
36.5
42.9
43.5
38.9
White
48.7
55.3
55.3
51.3
Other
51.3
44.7
44.7
48.7
Yes
27.1
25.5
14.6
31.4
No
72.9
74.5
85.4
68.6
Race/ethnicity
3.52
Smoker (last year)
0.28
Marital status
Never married
2.88
34.5
Other
0.06
0.60
0.09
29.1
65.5
Difficulty breathingb
70.9
29.36
Yes
20.7
8.6
No
79.3
91.4
Income (previous
year)
17.26
34.3
36.7
65.7
63.3
29.1
16.9
70.9
83.1
<0.01
<0.01
<$50,000
61.3
45.6
48.1
48.7
$50,000
38.7
54.4
51.9
51.3
x2
P
Value
1.07
0.59
1.43
0.23
0.31
0.58
0.22
0.64
6.09
0.01
0.09
0.77
2.99
0.08
0.00
0.95
a
The exposed group was defined as all survey participants living outside of Lower Manhattan (asthmatics and
nonasthmatics combined) in areas with estimated cumulative plume intensities (particulate matter concentrations) at
or above the 75th percentile. The unexposed group consisted of all remaining subjects.
b
Did the respondent have difficulty breathing because of smoke and debris during the event?
Cumulative estimated plume intensities
Figure 1 shows the cumulative probability of relative
plume intensity in Lower Manhattan (at or below 14th
Street), Upper Manhattan (above 14th Street), and all survey
areas outside of Lower Manhattan. Residents outside of
Lower Manhattan showed the greatest variability of relative
residential plume intensities. The plume intensities were
generally higher in Lower Manhattan than in the other areas,
with a median intensity that was nearly an order of magnitude greater than those in Upper Manhattan and areas outside of Lower Manhattan. Nevertheless, the 90th percentile
plume intensity for areas outside of Lower Manhattan was
similar to that for Lower Manhattan, indicating that after
exclusion of Lower Manhattan from some of our analyses,
many of the most highly exposed survey participants remained in the analyses. Mapping of the relative cumulative
plume intensity in areas excluding Lower Manhattan
showed that the 75th and 90th percentile exposures among
residents within this geographic area were predominantly in
the western half of Brooklyn (Figure 2). In Brooklyn, plume
intensities at the 75th and 90th percentile levels did not
appear to be correlated with distance from the WTC,
whereas in Manhattan higher intensities generally were
found in close proximity to the WTC. Figure 3 shows the
locations of residential addresses of subjects in the exposed
(75th percentile) and unexposed (<75th percentile)
groupings, which were used in the main analyses, in areas
surrounding the WTC site excluding Manhattan.
Survey results
In our survey data, we found no statistically significant
difference in odds of new-onset wheezing/coughing since
WTC Plume Intensity and Respiratory Symptoms
5
Figure 2. Residential cumulative particulate matter concentrations in the World Trade Center plume in the vicinity of Ground Zero following the
September 11, 2001, attack. The geographic distributions of modeled grid cells with cumulative relative plume intensity concentrations below the
75th percentile (pctl), within the 75th–90th percentiles, and above the 90th percentile are shown. The relative plume intensity values for these
percentile groupings were 0–0.00017, >0.00017–0.00060, and >0.00060–0.11, respectively.
Figure 3. Residential locations of survey participants in areas near the site of the World Trade Center collapse on September 11, 2001. Locations
with estimated cumulative plume intensities (particulate matter concentrations) greater than or equal to the 75th percentile and less than the 75th
percentile are designated by solid diamonds and open diamonds, respectively.
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Laumbach et al.
Table 2. Incidence of Wheeze/Cough and Worsening of Asthma Symptoms Among Persons Residing in the
Vicinity of the World Trade Center Collapse (Excluding Lower Manhattan) on September 11, 2001, by Exposure
Location, Spring 2002
Asthma Status
and Outcome
Nonasthmatics
Exposeda, %
Unexposed, %
Crude
OR
95% CI
Adjusted
ORb
95% CI
(n ¼ 411)
(n ¼ 1,130)
New-onset symptoms
(wheeze/cough)
16.1
13.3
1.3
0.8, 1.9
1.0
0.7, 1.7
Persistent new-onset
symptoms
5.6
4.6
1.2
0.6, 2.3
1.1
0.5, 2.3
(n ¼ 66)
(n ¼ 161)
Worsening of asthma
symptoms
13.9
16.6
0.8
0.3, 2.0
1.0
0.3, 2.8
Increase in nonroutine
asthma care
25.1
35.1
0.6
0.3, 1.3
0.5
0.2, 1.4
Asthmatics
Abbreviations: CI, confidence interval; OR, odds ratio.
Locations with cumulative relative plume intensities at or above the 75th percentile.
b
Odds ratio adjusted for age, sex, education, race/ethnicity, smoking status, marital status, and income.
a
asthma worsening or nonroutine asthma care when comparing Lower Manhattan with Upper Manhattan (Table 3).
We conducted 2 additional sensitivity analyses. Among
Manhattan residents only, we found that higher exposure to
the plume (at or above the 75th percentile) was not statistically significantly associated with increased new-onset or
persistent new-onset cough/wheeze, but results from analyses using the 90th and 95th percentiles were statistically
significantly associated (data not shown). When analysis
was limited to residents of Brooklyn, where the range of
plume exposures was also broad, we also did not see a statistically significant increase in new-onset respiratory symptoms at any of these percentile cutoffs (data not shown).
9/11 or persistent new-onset wheezing/coughing among
nonasthmatic residents who had cumulative residential exposures at or above 75th percentile compared with the
remaining subjects (Table 2). There also was no statistically significant difference among asthmatic responders in
reporting worsening asthma or nonroutine asthma care
since 9/11 when we compared those with residential exposures at or above the 75th percentile with those with
exposures below the 75th percentile.
To assess the comparability of our study with other, similar studies that focused on Manhattan residents and used
distance from Ground Zero as a proxy for exposure (9, 12,
13), we compared persons living in Lower Manhattan at
or below 14th Street with those living above 14th Street
(Table 3). Among nonasthmatic respondents, we found
statistically significant adjusted odds ratios for new-onset
cough/wheeze (odds ratio ¼ 1.9, 95% confidence interval
(CI): 1.1, 3.5) and persistent new-onset cough/wheeze (odds
ratio ¼ 2.5, 95% CI: 1.1, 5.9). Among asthmatics, we found
no statistically significant increased risk of self-reported
DISCUSSION
Our goal in this study was to assess whether the WTC
plume was associated with increased respiratory symptoms
among residents of New York City living beyond Lower
Manhattan. This study is the first we know of to have
Table 3. Incidence of Wheeze/Cough and Worsening of Asthma Symptoms Among Persons Residing in Lower
Manhattan (At or Below 14th Street) Versus Upper Manhattan (Above 14th Street) on September 11, 2001, Spring
2002
Asthma Status
and Outcome
Nonasthmatics
Lower
Manhattan, %
Upper
Manhattan, %
Crude
OR
95% CI
Adjusted
ORa
95% CI
(n ¼ 498)
(n ¼ 169)
New-onset symptoms
(wheeze/cough)
24.9
15.9
1.8
1.1, 2.9
1.9
1.1, 3.5
Persistent new-onset
symptoms
10.0
5.3
2.0
0.9, 4.4
2.5
1.1, 5.9
Asthmatics
(n ¼ 82)
(n ¼ 31)
Worsening of asthma
symptoms
17.6
21.8
0.8
0.2, 2.4
0.4
0.05, 2.8
Increase in nonroutine
asthma care
28.8
30.2
0.9
0.3, 2.5
0.9
0.2, 4.3
Abbreviations: CI, confidence interval; OR, odds ratio.
Adjusted for age, sex, education, race/ethnicity, smoking status, marital status, and income.
a
WTC Plume Intensity and Respiratory Symptoms
assessed the possible respiratory effects of the plume beyond
Lower Manhattan and to have used a continuous measure of
relative plume intensity, rather than binary residential location information, to infer exposures. Within the limitations
of our data, we saw no associations of plume intensity with
respiratory symptoms beyond Lower Manhattan.
Among residents who reported no previous diagnosis of
asthma, there were no statistically significant associations
between estimated plume intensities and new-onset or persistent cough/wheeze, using a plume intensity cutpoint of
the 75th percentile (Table 2) or higher or lower cutpoints of
the 50th, 60th, 70th, 80th, or 90th and 95th percentiles (see
Appendix Table 1 and Appendix Table 2). Among residents
who reported a previous diagnosis of asthma, there was no
statistically significant association between estimated plume
intensities and self-reported worsening of asthma symptoms
or nonroutine medical care for asthma. There were too few
asthmatics in the sample to conduct additional reliable
sensitivity analyses with higher exposure cutpoints.
Previous studies using binary exposure metrics based
principally on residential location found associations between living near Ground Zero and higher risk of respiratory
symptoms. In 2 studies (12, 13), investigators compared
exposed subjects who resided in apartment buildings within
1.5 km of Ground Zero with unexposed subjects living in
apartments at least 9 km from Ground Zero and north of the
site. Among previously asymptomatic persons, Reibman
et al. (13) found consistent and statistically significant elevations in levels of respiratory symptoms, with greater persistence, and increased use of respiratory medications
among persons living in the exposed areas as compared with
those living in unexposed areas, but no differences in
spirometry test results. For example, they reported elevated
crude incidence ratios for a number of new-onset respiratory
symptoms among previously asymptomatic residents, including ‘‘any cough without cold’’ (incidence ratio ¼ 3.36,
95% CI: 2.38, 4.74) and wheeze (incidence ratio ¼ 4.32,
95% CI: 2.68, 6.98). Among these subjects, Lin et al. (12)
found elevated levels of new-onset upper respiratory symptoms, unplanned medical visits for respiratory problems,
and respiratory medication use in exposed persons (12).
Limitations of these studies included response rates less
than 25%, the use of geographic location as the determinant
of exposure, and possible reporting bias.
To assess the consistency of our results with those from
previous studies, we compared responses among residents
of Manhattan living at or below 14th Street (about 3 km
north of Ground Zero), which includes persons living in
the area engulfed by the more intense event-related cloud
of dust and debris created by the WTC collapse, with responses among persons living above 14th Street (Table 3).
We found that among nonasthmatics, residents living at or
below 14th Street had statistically significantly increased
crude and adjusted odds of reporting new-onset cough/
wheeze and persistent new-onset cough/wheeze compared
with residents living above 14th Street, which is similar to
results reported in the other studies. Our smaller risk estimate may be due to smaller differences in exposure between
Manhattan populations living above and below 14th Street,
as compared with differences in exposure between the
7
exposed and comparison locations studied by Reibman
et al. (13). This is supported by our additional sensitivity
analyses, which showed statistically significant results in
our Manhattan-only analyses only using higher exposure
cutpoints (90th and 95th percentiles).
In contrast to other studies of asthmatics (10, 11), among
asthmatics we found no statistically significant increase in
self-reported worsening or nonroutine asthma care when comparing residents of Lower and Upper Manhattan (Table 3).
Because of the nature of the asthma severity survey question,
which assessed post-9/11 asthma severity in the 4 weeks prior
to the survey (several months after 9/11), we could not identify subjects who may have had acute exacerbations of asthma
that were resolved prior to the question’s time frame. Finally,
asthmatics who were most affected by their exposure may
have been underrepresented among participants because of
the large numbers of Lower Manhattan residents who relocated and had not returned as of June 2002, when the survey
was conducted (16).
Strengths and limitations
A strength of our study is that we assigned relative plume
intensities to individuals based on the results of sophisticated atmospheric dispersion modeling, which we believe
was more accurate than assigning exposures based on residence in broad geographic areas or distance from Ground
Zero. Observations and models indicated that the cumulative plume intensities were neither evenly distributed within
geographic areas nor closely correlated with distance from
the WTC. Furthermore, modeled plume intensities were less
likely than proximity to the WTC to be associated with selfidentification as exposed or not exposed, thereby reducing
the likelihood of biased recall of symptoms after 9/11.
In general, analysis of health outcomes in communities
exposed to air contaminants related to the WTC collapse has
been hampered by the lack of ‘‘real-time’’ exposure data and
limited outcome data. We based our estimates of relative
ground-level plume intensities on the dispersion properties
of a generic fine particulate aerosol. We calibrated these
estimates using satellite images and actual air monitoring
data collected at 4 stations close to the WTC. Despite these
efforts, possible explanations for the lack of association with
respiratory symptoms include misclassification of exposure.
The relative estimates of exposure did not account for
changes in chemical and physical characteristics of air contaminants, which occurred over time following the building
collapse. We limited our analysis to the 5-day period immediately following the collapse, because modeled concentrations after that time period made a negligible contribution to
cumulative exposure at any location. The location of survey
participants was based on residential address. We did not
have work location or any type of time-activity data with
which to link the locations of estimated particulate matter
concentrations with the locations of individual subjects over
time. In addition, large numbers of residents in the vicinity
of the WTC were displaced and therefore not captured by
the survey. Some of these displaced residents, who may
have had high initial exposures to the plume, were likely
to be residing at other locations in the survey area at the time
8
Laumbach et al.
of the survey. Finally, cumulative exposure may be less
biologically relevant than peak exposure for the respiratory
outcomes in this study, and we did not evaluate sensitive
subpopulations, including children with asthma and the
elderly.
Conclusions
We found no strong associations between estimated 5-day
cumulative residential WTC plume intensity beyond the immediate vicinity of the WTC and new-onset respiratory symptoms in nonasthmatics, or worsening asthma in asthmatics, on
the basis of community survey data. The estimated residential
plume intensities based on our dispersion modeling were the
best available exposure estimates, but differential or nondifferential exposure misclassification might have biased the
results towards our null findings. This study highlights the
need for a rapid epidemiologic and environmental response
capability to immediately follow up after other such events
(terrorist-driven or not), to improve our understanding of the
immediate and longer-term exposure hazards of these events
and their possible health effects.
ACKNOWLEDGMENTS
Author affiliations: Department of Environmental and
Occupational Medicine, University of Medicine and Dentistry of New Jersey–Robert Wood Johnson Medical School,
Piscataway, New Jersey (Robert J. Laumbach, Gerald
Harris, Howard Matthew Kipen, Panos Georgopoulos,
Pamela Shade, Sastry S. Isukapalli, Daniel Wartenberg);
Center for Global Health and Department of Epidemiology,
School of Public Health, University of Michigan, Ann
Arbor, Michigan (Sandro Galea); and New York Academy
of Medicine, New York, New York (David Vlahov).
This study was supported by the National Institute of
Environmental Health Sciences (grants K08 ES013520
and ES005022) and the Centers for Disease Control and
Prevention (grant 1 U19 EH000102).
The authors thank Dr. Thomas Matte for providing valuable ideas and comments from study conception through
manuscript preparation and for his contributions to the design and execution of the community survey.
Conflict of interest: none declared.
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(Appendix Tables 1 and 2 Follow)
WTC Plume Intensity and Respiratory Symptoms
Appendix Table 1. Incidence of Wheeze/Cough and Worsening of Asthma Symptoms by
Quartile of Cumulative Exposure to the World Trade Center Plume (Excluding Lower Manhattan),
Spring 2002
No. of
Subjectsa
Case %
Crude
OR
First
431
12.0
1.0
Second
354
15.8
1.4
0.8, 2.3
1.5
Third
347
12.2
1.0
0.6, 1.7
1.1
0.6, 1.8
Fourth
414
16.1
1.4
0.9, 2.3
1.2
0.7, 2.1
First
430
4.2
1.0
Second
354
5.4
1.3
0.6, 2.9
1.5
0.6, 3.6
Third
346
4.5
1.1
0.5, 2.4
1.4
0.6, 3.4
Fourth
411
5.6
1.4
0.6, 3.0
1.4
0.6, 3.5
First
62
11.9
1.0
Second
44
11.6
1.0
0.3, 3.5
0.9
0.1, 5.1
Third
56
26.4
2.6
0.8, 8.4
3.3
0.8, 13.4
Fourth
66
14.0
1.2
0.4, 3.9
1.5
0.3, 6.8
First
63
24.6
1.0
Second
44
41.0
2.1
0.8, 5.7
1.9
0.6, 6.0
Third
57
40.3
2.1
0.8, 5.2
2.5
0.9, 7.4
Fourth
66
25.1
1.0
0.4, 2.6
0.9
0.3, 3.0
Outcome and Quartile
95% CI
Adjusted
OR
95% CI
Nonasthmatics
New-onset symptoms
1.0
0.9, 2.5
Persistent new-onset
symptoms
1.0
Asthmatics
Worse symptoms
1.0
Nonroutine asthma care
Abbreviations: CI, confidence interval; OR, odds ratio.
Unweighted.
a
1.0
9
10
Laumbach et al.
Appendix Table 2. Incidence of Wheeze/Cough and Worsening of Asthma Symptoms Among Persons Residing in the Vicinity of the World
Trade Center Collapse (Excluding Lower Manhattan) on September 11, 2001, by Exposure Location, Using Alternative Percentile Cutpoints,
Spring 2002
Outcome
Case %
Exposed
Unexposed
Crude
OR
95% CI
Adjusted
OR
95% CI
785
14.1
13.8
1.0
0.7, 1.5
0.9
0.6, 1.4
923
15.4
13.1
1.2
0.8, 1.7
1.1
0.7, 1.6
504
1,042
17.3
12.6
1.5
1.0, 2.1
1.3
0.8, 2.0
75
414
1,132
16.1
13.3
1.3
0.8, 1.9
1.0
0.7, 1.7
80
344
1,202
15.8
13.5
1.2
0.8, 1.8
1.0
0.6, 1.7
90
95
1,451
13.8
14.0
1.0
0.5, 1.9
1.0
0.5, 2.0
50
757
784
5.0
4.7
1.1
0.6, 1.9
1.2
0.6, 2.2
60
619
922
5.5
4.5
1.3
0.7, 2.3
1.3
0.7, 2.5
70
500
1,041
6.1
4.4
1.4
0.8, 2.6
1.4
0.7, 2.8
75
411
1,130
5.6
4.6
1.2
0.6, 2.3
1.1
0.5, 2.3
80
341
1,200
4.3
5.0
0.9
0.4, 1.7
0.7
0.3, 1.7
90
95
1,446
5.0
4.9
1.0
0.4, 2.9
1.2
0.4, 3.6
50
122
106
20.3
11.8
1.9
0.8, 4.4
2.5
0.9, 6.9
60
99
129
17.8
14.8
1.2
0.5, 2.8
1.2
0.4, 3.2
70
82
146
17.7
15.2
1.2
0.5, 2.7
1.4
0.6, 3.7
75
66
162
13.9
16.6
0.8
0.3, 2.0
1.0
0.3, 2.8
80
53
175
12.2
16.9
0.7
0.2, 1.9
0.8
0.3, 2.6
90
12
216
20.7
15.8
1.4
0.3, 7.1
1.2
0.1, 12.8
50
123
107
32.9
32.5
1.0
0.5, 2.0
1.1
0.5, 2.4
60
99
131
32.3
33.0
1.0
0.5, 1.9
1.0
0.4, 2.2
70
82
148
27.8
34.9
0.7
0.4, 1.4
0.7
0.3, 1.6
75
66
164
25.1
35.1
0.6
0.3, 1.3
0.5
0.2, 1.4
80
53
177
24.4
34.7
0.6
0.3, 1.3
0.7
0.3, 1.8
90
12
218
19.3
33.4
0.5
0.1, 1.9
0.9
0.2, 5.1
Exposure
Cutpoint, %
No.
Exposeda
50
761
60
623
70
No.
Unexposeda
Nonasthmatics
New-onset symptoms
Persistent new-onset
symptoms
Asthmatics
Worse symptoms
Nonroutine
asthma care
Abbreviations: CI, confidence interval; OR, odds ratio.
Unweighted.
a