Unformatted text preview: ORIGINAL CONTRIBUTION Secondary Aerosolization of Viable
Bacillus anthracis Spores in a
Contaminated US Senate Office
Christopher P. Weis, PhD
Anthony J. Intrepido, MS, CIH
Aubrey K. Miller, MD, MPH
Patricia G. Cowin, MS, CIH
Mark A. Durno, BS
Joan S. Gebhardt, PhD
Robert Bull, PhD O N OCTOBER 15, 2001, A LET- ter containing threatening
language and a light tan
powdery substance was
opened in the mail handling area of a
Senate office suite in the Hart Senate Office Building, Washington, DC. Federal
officials removed the letter and shut
down the local air handling systems. The
letter was transported to the US Army
Medical Research Institute of Infectious Disease and was subsequently confirmed to contain viable Bacillus anthracis (anthrax) spores that were dispersible
in air.1 Scanning electron microscopy of
the spores used in the Senate office attack showed that they ranged from individual particles to aggregates of 100 µm
or more. Spores were uniform in size and
appearance and the aggregates had a propensity to pulverize1 (ie, disperse into
smaller particles when disturbed).
Following the attack, nasal swabs
were collected by other investigators
from more than 7000 building occupants and cultured for B anthracis.
Twenty of 38 individuals in the office
suite where the envelope was opened
had positive nasal swab tests including 13 individuals present in the vicin- Context Bioterrorist attacks involving letters and mail-handling systems in Washington, DC, resulted in Bacillus anthracis (anthrax) spore contamination in the Hart
Senate Office Building and other facilities in the US Capitol’s vicinity.
Objective To provide information about the nature and extent of indoor secondary
aerosolization of B anthracis spores.
Design Stationary and personal air samples, surface dust, and swab samples were
collected under semiquiescent (minimal activities) and then simulated active office conditions to estimate secondary aerosolization of B anthracis spores. Nominal size characteristics, airborne concentrations, and surface contamination of B anthracis particles (colony-forming units) were evaluated.
Results Viable B anthracis spores reaerosolized under semiquiescent conditions, with
a marked increase in reaerosolization during simulated active office conditions. Increases were observed for B anthracis collected on open sheep blood agar plates (PϽ.001)
and personal air monitors (P=.01) during active office conditions. More than 80% of
the B anthracis particles collected on stationary monitors were within an alveolar respirable size range of 0.95 to 3.5 µm.
Conclusions Bacillus anthracis spores used in a recent terrorist incident reaerosolized under common office activities. These findings have important implications for
appropriate respiratory protection, remediation, and reoccupancy of contaminated office environments.
www.jama.com JAMA. 2002;288:2853-2858 ity of the mail area and 7 workers on
an interconnected lower floor. Additionally, 2 workers from an adjacent office suite that entered an adjoining contaminated hallway and 6 emergency
responders who entered the office or
hallway had positive nasal swab tests.
The building was officially closed to
the public on October 17, 2001, with
access to the contaminated suite limited to forensic investigators only. This
study was completed after forensic investigation and prior to remediation of
the Hart Senate Office Building.
Information regarding primary aerosolization of B anthracis spores has been
reported,2-5 but few data are available
regarding secondary aerosolization in- ©2002 American Medical Association. All rights reserved. doors. The purpose of this investigation was to evaluate secondary aerosolization of viable B anthracis spores
under both quiescent and active office
conditions. Understanding secondary
aerosolization (reaerosolization) of
Author Affiliations: US Environmental Protection
Agency National Enforcement Investigations Center,
Denver Federal Center, Denver, Colo (Dr Weis); US
Army Center for Health Promotion and Preventive
Medicine, Aberdeen Proving Ground, Md (Mr Intrepido and Ms Cowin); US Public Health Service, Denver, Colo (Dr Miller); US Environmental Protection
Agency Region 5, Cleveland Office, Westlake, Ohio
(Mr Durno); and Naval Medical Research Center, Biological Defense Directorate, Silver Spring, Md (Drs Gebhardt and Bull).
Corresponding Author and Reprints: Christopher P.
Weis, PhD, US Environmental Protection Agency National Enforcement Investigations Center, Denver Federal Center, Bldg 53, PO Box 25227, Denver, CO
80225 (e-mail: [email protected]). (Reprinted) JAMA, December 11, 2002—Vol 288, No. 22 2853 SECONDARY AEROSOLIZATION OF BACILLUS ANTHRACIS SPORES B anthracis spores in building environments is essential for exposure assessment and risk evaluation following bioterrorism attacks. Such understanding
will also guide cleanup strategies for
readily dispersible bioaerosols.
Environmental samples were collected in the affected Senate office suite (total area approximately 1200 sq ft) beginning 25 days after the initial incident. Stationary and personal air
samples and surface samples were collected during 3 separate building entries (TABLE 1). Initial semiquiescent
sampling was followed by second and
third rounds of sampling under simulated active office conditions. All analyses were conducted such that only vi- Table 1. Chronology of Secondary Aerosolization Sampling in the Hart Senate Office
Building After the Primary Aerosolization Event on October 15, 2001*
November 10, 2001
Sampling) November 10, 2001
PM (1st Active
Sampling Period) 3 3 November 15, 2001
1 NA NA 2 9 9 3 Personal breathing zone
Passive SBA plates
(breathing zone level)
Surface swab samples *SBA indicates sheep blood agar (5%); NA, not applicable. Environmental samples for Bacillus anthracis were collected in the Senate suite following the initial forensic investigation and prior to remediation. The types of samples
collected, the number of samples in each category, and the collection schedule are presented. Figure. Active and Passive Environmental Sample Locations in the Hart Senate Office Building D C 0; 11 0; 15 0; 25 0; 80 1; NA 0; 20 0; 13 0; 12 A 3; 48
0; 8 1; 32 1; 38 0; 28
B Mail Desk Entrance E 0; 19 0; 4 1; 15 0; 0
Semiquiescent and First Active Sampling Periods Second Active Sampling Period 6-Stage Andersen Sampler (Floor) 6-Stage Andersen Sampler (Breathing Zone) Open Sheep Blood Agar Plate (Chair) 2-Stage Andersen Sampler (Floor) Open Sheep Blood Agar Plate (Floor) Microvacuum Surface Swab Surface Swab
Note: Drawing not to scale NA indicates not available. Numerical values of viable Bacillus anthracis colonies represent passive samples
collected by placing open sheep blood agar plates during semiquiescent and first active sampling periods (semiquiescent; first active). Surface swab samples in the second active sampling period had no corresponding control samples.
2854 JAMA, December 11, 2002—Vol 288, No. 22 (Reprinted) able spores or spore aggregates were
During semiquiescent sampling,
movement was minimized in the suite
while air and surface samples were collected from various locations. During the
semiquiescent sampling, the sample
team (wearing sterile gloves, boots,
hooded protective suits, and powered air
purifying respirators with P.100 cartridges) placed sampling devices in the
locations indicated in the FIGURE and left
the suite to reduce air turbulence for the
duration of the sample collection period. Following semiquiescent sampling, active office conditions were simulated to reflect routine behaviors in a
busy office environment (ie, paper handling, active foot traffic, simulated mail
sorting, moving trash containers, patting chairs). There was no activity in the
office suite several days prior to or between sampling periods.
There are no validated environmental sampling or risk assessment methods for B anthracis contamination.
Questions regarding collection techniques, laboratory extraction efficiency from environmental media, and
appropriate methods for air monitoring remain unanswered. Accordingly,
in this investigation a variety of environmental sampling methods were used
to assess their usefulness for estimating environmental exposure and risk
from B anthracis spores. Samples and
sample locations were based on plausible exposure pathways (both inhalation and dermal) and were selected
based on proximity to the original release, pedestrian traffic patterns within
the suite, representative exposures to
the staff in the work area, and areas of
interest for spore transport within the
office suite (eg, computer monitors).
Environmental sampling methods included air monitoring with stationary
and personal sampling devices (devices
worn by the sample team to characterize colony-forming unit [CFU] levels in
their breathing zone) that actively collected spores from a known volume of
air as well as open blood agar plates that
passively collected spores deposited from
the Hart Senate Office Building aerosol. ©2002 American Medical Association. All rights reserved. SECONDARY AEROSOLIZATION OF BACILLUS ANTHRACIS SPORES Surface samples were collected to help
characterize the presence of B anthracis
contamination on a variety of surface
types using both microvacuum devices
and sterile swabs. These environmental
samples were collected under both quiescent and active office conditions to assess the influence of human movement
within the suite on environmental spore
Andersen 6-stage viable (microbial)
particle-sizing samplers (ThermoAndersen, Smyrna, Ga) were used to collect airborne spores to evaluate concentrations and size ranges of spores or spore
aggregates. Andersen samplers were operated for 10 minutes at an air flow rate
of 28.3 L/min during each sample collection period. The Andersen sampler
collects spores according to nominal
aerodynamic diameters on each of 6 vertically stacked agar plates. Andersen samplers use petri dishes filled with 42 mL
of agar to control aerodynamics of particle impact on plates according to manufacturer-specified cutoffs of 7.0, 4.7, 3.3,
2.1, 1.1, and 0.65 µm. For this investigation, 18 mL of 5% sheep blood agar
(SBA) plates (Remel Inc, Lenexa, Kan)
were used for collection media. Use of
reduced media volume resulted in an increase in the specified jet-to-plate distance of 0.3 cm with a corresponding increase of 0.3 µm in the particle size
cutpoints.6 Thus, the smallest particle impacting the number 6 plate in the cascade would have a nominal diameter of
0.95 µm (ie, 0.65 µm + 0.3 µm).
For the semiquiescent and the first active testing period, 2 viable Andersen impact samplers (6-stage) were used; 1 was
placed on the floor in the vicinity of the
original contamination and 1 was placed
on the floor 20 feet away near the common entrance to the suite (Figure). During the second active sampling period,
the 2 Andersen samplers were placed at
the breathing zone level in the same locations, and a specially configured
2-stage Andersen sampler was placed at
a floor location near the original source
zone. The final stage of this sampler was
fitted with a glass fiber filter to trap any
remaining viable spores smaller than the
final impact stage (approximately 0.9 Box. Positive Hole Correction Method
The positive hole correction method determines a statistical probablility count of
colony-forming units. It represents a count of the jets that delivered the spores to
the agar plates and the conversion of the jet number to a particle count by using
the “positive hole” conversion formula7:
r+1 Pr=N ϫ ͚
x=0 ͩ ͪ
1 N−x where Pr is the expected number of viable particulates to produce r positive holes
and N is the total number of holes per stage (400). This formula is based on the
principle that as the number of viable particles being impinged on a given plate
increases, the probability of the next particle going into an unpenetrated hole decreases. Thus, when 9 of 10 of the holes have each received 1 or more particles,
the next particle has but 1 chance in 10 of going into an unpenetrated hole. Therefore, on average, 10 additional particles would be required to increase the number
of positive holes by 1. Table 2. Stationary Air Samples of Viable Bacillus anthracis Particles*
No. of CFUs (No. Based on Positive Hole Correction Method)
Mail Handling Area
170 (171) Entrance Area Active Conditions
2611 (Ͼ11 000) Breathing
653 (707) Semiquiescent
244 (251) Active Conditions
244 (721) Breathing
106 *CFUs indicate colony-forming units. Samples were collected on 6-stage Andersen sampling devices designed to register nominal spore size for viable particles. µm). At the end of each sample collection period, Andersen samplers were disinfected to avoid cross-contamination.
Direct colony counts on SBA plates
in the Anderson samplers were obtained and the positive hole correction method (BOX) was used to acquire a statistical probability count of
CFUs (TABLE 2).
In addition to stationary air samples,
personal air samples were collected
from the breathing zone of sample team
members during all 3 rounds of sampling. Sample pumps were calibrated to
operate at a flow rate of 4 L/min. The ©2002 American Medical Association. All rights reserved. flow rate was not intended to simulate
respiratory minute ventilation but to
provide efficient deposition of spores
on the collection media. Collection media consisted of gelatin filters placed in
37-mm open-faced filter cassettes and
located in breathing zones of team
members for each sampling period.
These cassettes are commonly used for
personal air monitoring applications
and were available with corresponding gelatin inserts conducive to the collection and direct incubation of microbial samples. Sample cassettes were
placed on the front of the team mem- (Reprinted) JAMA, December 11, 2002—Vol 288, No. 22 2855 SECONDARY AEROSOLIZATION OF BACILLUS ANTHRACIS SPORES bers’ suits just below the shoulder and
connected to a sampling pump worn at
the waist by a length of Tygon tubing
(Saint-Gobain Performance Plastics
Corporation, Akron, Ohio).
Open plates were placed in workstations, on the floor, and within the stairway to estimate spore settling during and
following various levels of human activity in the suite. Seventeen SBA plates
were placed in various locations and at
various heights throughout the office
during the semiquiescent and the first
active sampling period. Ten plates were
placed on office chairs, 3 at various floor
locations, and 4 on the steps of an internal office stairway (Figure). Plates
were opened for 45 minutes to collect
viable spores then closed and wrapped
A total of 17 surface samples were collected on fabric office dividers, carpets,
paper files, and near the source of
the original contamination. A microvacuum sampler was used to quantify the
surface loading of B anthracis on a variety of surface types. Microvacuum
samples were collected using personal air
monitoring pumps operated at a calibrated flow rate of 4 L/min. Filter cowls
containing gelatin filters with a nominal pore size of 3 µm (having submicron retention efficiencies) were connected to the pump with tubing to form
a microvacuum device. Sampled areas
were defined by a 100-cm2 template, then
vacuumed using a slow back and forth
motion first in one direction, and then
perpendicular to the original direction.
Microvacuum samples were collected at
workstations in 5 different office areas
during the second active sampling period.
Swab samples were used to assess the
presence of B anthracis contamination
on an additional 12 surfaces. Sterile nylon swabs moistened with sterile water
were used to sample both vertical and
horizontal surfaces as defined by 100cm2 templates. Areas were swabbed in
perpendicular directions using a slowly
progressing S-shaped motion and then
placed in sterile 15-mL tubes. Nine swab
samples were collected for both the semiquiescent and first active sampling periods: 3 vertical semigloss latex painted
2856 surfaces (2 doors and 1 wall), 3 computer monitors, and 3 individual mailboxes.
Aseptic handling techniques were
used throughout the sampling and analytical process. All samples were labeled immediately following collection
using predetermined sample codes.
Samples were placed in individual resealable bags and immediately shipped
to the analytical laboratory with blind
identification codes and under chainof-custody. Field blank samples (qualitycontrol samples used to ensure adherence to sterile microbiologic technique)
were included at a frequency of 10%.
Samples were evaluated for the presence of viable B anthracis at the Naval
Medical Research Center in Silver
Spring, Md. Gelatin filters were removed from the filter cassettes and
placed directly on SBA plates. Swabs and
glass fiber filters were macerated in 3.0
and 7.5 mL, respectively, of sterile phosphate-buffered saline for approximately 1 minute to free viable spores.
Following maceration, a 1.0-mL aliquot of each sample was removed and
heat shocked at 65°C for 15 minutes to
reduce viable vegetative bacteria in the
sample. A 200-µL aliquot of each heated
sample was spread on an SBA plate and
plates were incubated at 37°C for 14
hours. Following incubation, bacterial
colonies morphologically consistent
with B anthracis were counted and recorded. Rapid real-time polymerase
chain reaction assays were used to confirm the identity of suspect B anthracis
colonies.8,9 At least 1 suspect colony from
each plate was tested for the presence of
the genetic markers pag and cyaB, specific to the virulence plasmids pXO1 and
pXO2, respectively. Following polymerase chain reaction confirmation of selected suspect colonies, the number of
B anthracis colonies on each plate was
reported. Analyse-It Software version
1.64 (Analyse-It Software Ltd, Leeds, England) was used for statistical analyses
and PϽ.05 was considered significant.
All sample team members were specially trained in response to extremely
hazardous environments and all participation was voluntary. The US Federal JAMA, December 11, 2002—Vol 288, No. 22 (Reprinted) Incident Command System reviewed
and approved the study. Incident Command System is a system used to organize and manage participating groups
during emergency response situations.
Results for the 6-stage Andersen air
samples are presented in Table 2. Positive hole correction results are presented below where applicable. Comparison of floor samples between
semiquiescent and active conditions
showed an increase in viable spore collection across all sampler stages at both
the mail area (48 vs Ͼ3006 total CFUs)
and entrance area (71 vs 204 total CFUs)
locations. In the mail area, stationary
Andersen breathing zone samples
showed an increase compared with semiquiescent sampling taken previously at
floor level (200 vs 48 total CFUs). Estimated airborne spore concentrations
collected near the floor over a 10minute period ranged from 171 to 251
CFUs/m3 during the semiquiescent period. For the active period, airborne CFU
concentrations ranged from 721 to more
than 11000 and 106 to 707 CFUs/m3 for
floor and breathing zone samples, respectively. This represents as much as a
65-fold increase in CFUs under active
conditions compared with semiquiescent
conditions. Approximately half of the
CFUs had corrected nominal diameters
ranging from 1.4 to 2.4 µm, with more
than 80% ranging from 0.95 to 3.5 µm.
Results from the 2-stage Andersen sampler indicated no viable spores less than
a corrected nominal diameter of 0.95 µm.
Locations and results of viable colony
counts on the 17 open SBA plates (10 on
chairs; 7 on the floor) collected during
semiquiescent and active periods are
shown in the Figure. During the semiquiescent period, 5 of the 17 plates were
positive for B anthracis (median, 0 CFU;
range, 1-3 CFUs; 95% confidence interval [CI], 0-1). In comparison, 14 of 15
plates (1 plate was left in the suite and
was desiccated beyond use) during the
first active sampling period were positive for B anthracis (median, 15 CFUs;
range, 4-80 CFUs; 95% CI, 11-28) illustrating a significant increase in colony ©2002 American Medical Association. All rights reserved. SECONDARY AEROSOLIZATION OF BACILLUS ANTHRACIS SPORES Table 3. Personal Air Monitoring Results*
3 No. of
3 Estimated Air
6.0 Active Period 1
1 Estimated Air
3.3 Active Period 2 P Value
.17 No. of
22 Estimated Air
49.1 P Value
.01 *CFUs indicate colony-forming units. Results for the personal air monitors represent exposures integrated over the total time spent in the Hart Senate Office Building. During quiescent sampling the team spent more than half of the time in less contaminated hallway areas; therefore, results may underestimate exposure in more contaminated areas of the
suite. P value comparisons with semiquiescent sample measurements. counts (PϽ.001; using a 2-tailed nonparametric Wilcoxon signed rank test).
Results of personal air monitor
samples collected from team members
during each of the sampling periods are
presented in TABLE 3. Filters from all
10 of the samples were positive for B
anthracis. Results were positive for B anthracis during semiquiescent office conditions (mean, 4 CFUs; range, 1-7
CFUs) and increased during active office conditions (mean, 14 CFUs; range,
1-36 CFUs). There was a significant increase in the number of CFUs collected on personal air samples during
the second active test period (P = .01;
1-tailed paired t test with 2 df) but not
the first active test period (P=.17) when
compared with the semiquiescent sampling period. A 1-tailed statistical test
was used with the expectation that the
number of airborne viable CFUs would
increase (rather than decrease) when
activity increased in the suite.
Six of the 9 surface swab samples taken
during the semiquiescent and first active period were positive; 3 vertical mailbox surfaces (range, 3-43 CFUs) and 3
computer screens (range, 2-150 CFUs),
with little change in viable spore counts
in response to increased activity. Three
swab samples collected from vertical wall
surfaces during each sampling period
were negative. During the second active sampling period, sequential swab
samples of a computer monitor screen
sampled in the off, then on position, resulted in a 25-fold increase in viable
colony counts on the charged screen.
Deposition of spores on the charged
monitor may indicate influence of electrostatic effects on spore behavior.
Additionally, 5 microvacuum
samples were taken in different office Table 4. Microvacuum Samples Collected in the Hart Senate Office Suite During Second
A (Mail area)
E (Workstation) Carpet
4600 Fabric Office Dividers
0 Smooth Horizontal
2500 Tops of Files
0 *Ellipses indicate too numerous to count; NA, not applicable; and CFUs, colony-forming units. Microvacuum samples of selected 100-cm2 surfaces within the office suite. Homogeneity of spore distribution across surface areas sampled
should not be assumed. areas during the second period of activity to evaluate contamination of different types of surfaces (TABLE 4). Although microvacuum samples showed
substantial viable spore contamination of carpeted and smooth horizontal surfaces, very little contamination
of vertical fabric workstation dividers
or the tops of paper files was found. No
CFUs were found on the field blanks
collected from any of the sample types
during the course of the investigation.
The importance of secondary aerosolization of B anthracis spores associated
with a bioterrorism attack has been discussed by a number of researchers.10-14
However, few empirical data existed to
allow for scientifically based public health
conclusions or recommendations. Although research conducted by the military has shown that Bacillus subtilis
spores, used as a surrogate for B anthracis, can reaerosolize with varying activities in outdoor environments,13,15 until
now, no published data have been available concerning secondary aerosolization of B anthracis spores indoors. Prior
to the attacks in the fall of 2001, con- ©2002 American Medical Association. All rights reserved. sensus recommendations from the
Working Group on Civilian Biodefense11 suggested only a slight risk of acquiring inhalational anthrax by secondary reaerosolization from heavily
contaminated surfaces. These recommendations were based on an incident
involving accidental release of B anthracis in Sverdlovsk, Russia,5 occupational
studies of workers in goat hair processing mills,16 and modeling analyses by the
US Army.12 The Working Group on
Civilian Biodefense recognized that its
recommendations were based on interpretation and extrapolation from an incomplete knowledge base and needed to
be regularly reassessed as new information becomes available.11 A recent reassessment by the consensus group includes a precautionary note regarding
reaerosolization of B anthracis spores
based, in part, on work presented here.17
This investigation presents empirical findings concerning secondary aerosolization of viable B anthracis spores
following a bioterrorism incident indoors. Among the limitations of the
work are the severe schedule constraints, limited availability of equipment, and the extreme conditions un- (Reprinted) JAMA, December 11, 2002—Vol 288, No. 22 2857 SECONDARY AEROSOLIZATION OF BACILLUS ANTHRACIS SPORES der which the investigation was planned
and implemented. Both empirically observed and substantially increased spore
concentrations were recorded on open
SBA plates during active conditions in
the office suite. Elevations of CFUs recorded on personal air monitoring devices during active vs semiquiescent office conditions are consistent with
military investigations showing activityrelated increases in airborne spore exposures outdoors.13 However, the personal air monitor data reported in this
study are limited due to high variability and small sample size.
During simulated activities, airborne concentrations of viable B anthracis spores within the office ranged
from 2 to 86 CFUs/m3 for personal air
monitors and 100 to more than 11 000
CFUs/m 3 for stationary Andersen
samples, with more than 80% of the
spores falling into the respirable range
(Ͻ5 µm). Relatively higher collection
efficiencies on stationary monitors may
be due to sample locations within the
contaminated suite, higher air flow rates
through the stationary sampling devices, or the sample team personal
monitors integrating exposure over
both contaminated and noncontaminated areas of the Hart Senate Office
Building (personal monitors were activated on entry to the building 6 floors
below the contaminated suite).
Using a mean (SD) respiratory rate of
1.38 m3/h (0.66) reported for office workers,18 estimated inhalation exposures to
B anthracis in the breathing zone were
119 and 250 CFUs/h for personal air
monitors and breathing zone Andersen
samplers, respectively. Based on CFU
concentrations recorded by floor level
Andersen samplers, estimated exposures were as high as 15000 CFUs/h. Additionally, findings of airborne B anthracis spores during the initial semiquiescent
sampling period suggest that even minimal movements may result in resuspension of viable spores. These findings were
recorded almost a month following the
original incident, despite the removal of
the contaminated letter from the suite.
Determining the magnitude of inhalational risks from reaerosolized B an2858 thracis spores is uncertain. Reliable human data on the minimum infective dose
for inhalational B anthracis is lacking. Individual susceptibility, virulence of the
strain, and spore physical characteristics may all have profound impacts on
the dose necessary to cause inhalational anthrax.3,4 Primate model extrapolations suggest an estimated human median lethal dose between 2500 and 55000
spores,10 with the highest infectivity associated with clouds of single spores, vs
multispore aggregates.4 Recent primate
studies have demonstrated inhalational
infectivity of B anthracis following exposure to only a few spores.19 Human
cases of inhalational anthrax have also
been reported involving minimal exposures.16 Risk predictions indicate that infective doses may be as low as 1 to 3
spores14 and these predictions may be reflected in the 2 cases of inhalational anthrax in New York and Connecticut still
This work clearly demonstrates a potential for secondary aerosolization of viable B anthracis spores originating from
contaminated surfaces in an indoor environment. As a result, precautions to
protect exposed decontamination workers and area occupants are indicated.
Author Contributions: Study concept and design:
Weis, Miller, Durno.
Acquisition of data: Weis, Intrepido, Miller, Cowin,
Durno, Gebhardt, Bull.
Analysis and interpretation of data: Weis, Intrepido,
Miller, Cowin, Durno, Gebhardt, Bull.
Drafting of the manuscript: Weis, Intrepido, Miller,
Critical revision of the manuscript for important intellectual content: Weis, Miller, Durno, Gebhardt, Bull.
Statistical expertise: Weis, Miller.
Obtained funding: Weis.
Administrative, technical, or material support: Weis,
Intrepido, Miller, Cowin, Durno, Gebhardt, Bull.
Study supervision: Weis, Durno, Gebhardt, Bull.
Funding/Support: Funding and/or resources for this
investigation were provided by the participating federal agencies.
Disclaimer: The views, opinions, assertions, and findings contained herein are those of the authors and should
not be construed as official US agency policies or decisions unless so designated by other documentation.
Any reference to products or methods does not constitute an endorsement of those products or methods
by the authors or by the US federal government.
Acknowledgment: In support of this work, we graciously acknowledge the US Capitol Police for their hospitality, sample transport, and site security during the
incident; the Capitol Hill Incident Commander for spirited leadership and endless encouragement; US Architect of the Capitol for providing tireless engineering and
architectural advice; US Environmental Protection
Agency management and especially the EPA On- JAMA, December 11, 2002—Vol 288, No. 22 (Reprinted) Scene Coordinators; Bill Daniels, MS, CIH, CSP, of the
US Public Health Service for invaluable advice on sampling, study design, and detailed editorial recommendations; Chris Ansell, MS, of Center for Health Promotion and Preventive Medicine for assisting with project
logistics; and the laboratory technicians at Naval Medical Research Center for many hours of analysis. REFERENCES
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