Risk Assessment: Release of Anthrax in an IRS Building
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Risk Assessment: Release of Anthrax in an IRS Building
Team Members:
Amanda H., Claudia R., Kyle E., Meghan M., Oliver B., Phares O, Stephanie L.T., Yin H.
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Outline What is anthrax?
Case Study Scenario
Transport of Particles
Dose Response
Exposure Assessment Decision tree Acceptable risk
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Outline cont’d Sampling
Sites Recovery Protocols Detection Methods
Stakeholders Remediation
Decontamination Procedure (explain method and acceptable limit
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Problem
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What is Anthrax?
Bacillus anthracis Gram positive spore forming rods Very resistant spores Survive in the environment for extended periods of time Used as a biological weapon
Mortality Inhalation → ~75% Cutaneous → ~20% Ingested → ~25 – 60%
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Weaponized Anthrax Spores
http://cryptome.org/anthrax-powder.jpg
particle of zinc sulfide coated with silica. The zinc sulfide particle is about 2 microns across (similar in size to an anthrax spore), and thesilica particles are about 100 nanometers
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Aerosolized Anthrax
Radiographic examination of the chest often reveals characteristic mediastinal widening, indicative of hemorrhagic mediastinitis
http://www.youtube.com/watch?v=WNRgLkjaRlY
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Scenario
Package containing anthrax spores opened in office with 5 desks
Quickly aerosolized & dispersed
30 min before hazard recognized & personnel evacuated
Environmental sampling is needed
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Transport Zones
Coffee
Printer& Copier
40 feet
30 feet wide13 feet high
Air Vent
Air Vent
Plant
Plant
window
Break Area with chairs
Not-to-scale
Air Vent
Air Vent
Air flow
ZONE 1
10 feet 10 feet 10 feet 10 feet
ZONE 2ZONE 3ZONE 4
Scenario
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Particle Transport
Total Room Volume: V = 441 m3
Zone Volume: Vzone = 110 m3
Air Flow conforms to ASHRAE Standard 62 – requires 6 air exchanges per hour 0.7 m3/s
First order decay based on air flow Neglect settling due to gravity (for 30 minute duration)
settling due to particle size
Calculate the Concentration (# particles/m3) based on time
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Range in particle concentration (#particles/m^3) in room after 1 air exchange
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
7.00E+07
8.00E+07
9.00E+07
1.00E+08
0 10 20 30 40
Distance in Room (10 ft Zones)
# p
art
icle
s/m
^3
ZONE 1 Instant ZONE 2 ZONE 3 ZONE 4
Explosion Zone
Particle concentration Range reaching each Zone during 1 Air Turnover
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
7.00E+07
8.00E+07
9.00E+07
1.00E+08
0.00 0.00 2.63 5.26 7.89
ZONE 1 Instant ZONE 2
Receives Max Concentration spores diluted in room volume
SENIOR MANAGER
1e10 colonies - 9e7 colonies
ZONE 3 ZONE 4
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Log Scale - 1e10 particles in explosion for Zone 1
1.00E+001.00E+011.00E+021.00E+031.00E+041.00E+051.00E+061.00E+071.00E+081.00E+091.00E+10
0
2.63
5.26
7.89
10.5
2
13.1
5
15.7
8
18.4
1
21.0
4
23.6
7
26.3
28.9
3
31.5
6
Time (minutes)
# pa
rticl
es/m
3
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Removal of Particles by ventilation in Office ZONE 4
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
7.00E+07
8.00E+07
9.00E+07
0
2.63
5.26
7.89
10.52
13.15
15.78
18.41
21.04
23.67 26
.3
28.93
31.56
Time (minutes)
# par
ticles
/m3
Removal of Particles by ventilation in Office ZONE 3
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
7.00E+07
8.00E+07
9.00E+07
0
2.63
5.26
7.89
10.52
13.15
15.78
18.41
21.04
23.67 26
.3
28.93
31.56
Time (minutes)
# par
ticles
/m^3
Removal of Particles by ventilation in Office ZONE 2
0.00E+00
1.00E+07
2.00E+07
3.00E+07
4.00E+07
5.00E+07
6.00E+07
7.00E+07
8.00E+07
9.00E+07
0
2.63
5.26
7.89
10.52
13.15
15.78
18.41
21.04
23.67 26
.3
28.93
31.56
Time (minutes)
# part
icles
/m3
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Dose-Response: Data LD50 = ED50
In the literature, LD50 ranges several orders of magnitude (2500 to 155,000)
Frequently cited human estimates ranging from 4100 to 8000.
LD5 = 14 -28 LD2 = 4-7 LD1 = 1-3
Even a single spore results in a risk of 1/100
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Dose-Response: Model
P(d) = 1/100 d=1075-1813
spores
P(d) = 1/10,000 d=11-18 spores
Dose Response
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
10 1̂ 10 2̂ 10 3̂ 10 4̂ 10 5̂ 10 6̂ 10 7̂ 10 8̂ 10^9
Dose
P(d
)
LD50 = 74100
LD50=94320
LD50 = 125060
Bartrand et al. 2008
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Dose-Response: Assumptions
Human potency information can be extrapolated from animal data
Uniform strain
Uniform size - small
Time does not have a significant effect on cumulative dose
Human response is uniform
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Model assumptions ‘k’ parameter for exponential model
Triangular dist.; min 5.54e-6, mean 7.00e-6, max 9.35e-6 (Bartrand et al. 2008)
Inhalation rate, m^3/h Normal dist.; mean 5.6, SD 0.114 (Adams 1993)
Attempted to randomly distribute, but failed due to technical problems: Number of spores released (1e10) Ventilation rate of room (assumed accurately measured)
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Modeling approach Given room air turnover rate, size of room, and # of
spores released: Determined # of spores in each room section, on
average, over 30m Given the above, with inhalation rate:
Determined # of spores inhaled per person in each zone of room
Given the above, with ‘k’ parameter: Determined risk using the exponential model for
each zone of room
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Initial exposure risk results
Zone of room
Risk of death:
Mean
Risk of death:
SD
1 1.00 0.00
2 0.56 0.08
3 0.26 0.05
4 0.11 0.02
‘k’ contributed 20% of the variation;
Inhalation rate contributed 80% of the variation.
There were 1000 Monte Carlo trials.
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Prophylaxis by Doxycycline
Yes
No
Yes q=80%p
No 1-q=1-80%p
No 1-p=10%
Yes p=90%
$0
$52
$6milion(VSL)+$52
$6milion(VSL)
Death
Death
Decision Tree
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Acceptable Risk
E [prophylaxis] = E [no prophylaxis]
E [prophylaxis] = (value of statistical life + cost of doxycycline + cost of prescription) × q + (cost of doxycycline + cost of prescription) ×(1-q)
E [no prophylaxis] = value of statistical life × p + 0 × (1-p)
P= 4.33 × 10-5
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CLINICAL SYMPTOMS / TRANSMISSION ROUTE
Form Symptoms Frequency Route of acquisition
Ulceroglandular or glandular
Skin ulcer, lymph node enlargement, fever, chills, headache
75-85%
65%
Vector-borne and direct contact
Oculoglandular Fever, conjunctivitis, photophobia, glaucomatous lesions
<1%
4%
Touching the eye with contaminated fingers or possibly from infective dust
Oropharyngeal Ulcerative-exudative stomatitis, pharyngitis, lymphadenitis, vomiting, diarrhea
1% Ingesting contaminated food or water
Respiratory Cough, chest pain, increased repiratory rate, fever, nausea, vomiting
17% Inhaling contaminated dust or laboratory-acquired infection
Typhoidal Fever, weight loss, diarrhea and pain
12% Unknown (probably oral or respiratory)
Fonte: WHO,2007; Staples, 2006
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Surface Sampling Method
40% 93%
D.L.=12 CFU/cm2
(4 papers-Surfaces)
D.L.=430 CFU/mL (18 papers-Instrument)
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Air Sampling Method
The ASD features an air sampler, a thermal lysis unit, a syringe pump, a time-gated spectrometer, and endospore detection chemistry comprised of dipicolinic acid (DPA)-triggered terbium ion (Tb3+) luminescence
D.L.=50 spores/L (2 papers)
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Sampling Zones
Coffee
Printer& Copier
Senior Manager
40 feet
30 feet
Air Vent
Air Vent
Plant
Plant
Air flow
window
Break Area with chairs
Not-to-scale
Air Vent
Air Vent
10 feet 10 feet 10 feet 10 feet
30 million surface samples (95% confidence)
=surface sampling =air sampling
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Who Cares???
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Remediation
H2O2 gas effective in inactivating Bacterial spores Vegetative bacterial cells Viruses Prions
Less toxic than other fumigants Chlorine dioxide Ethylene oxide Formaldehyde
Breaks down to O2
H20
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Remediation
Uses: decontamination
Lab & medical equipment Pharmaceutical facilities Hospital rooms Animal holding rooms
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Remediation
Acceptable overall Risk 4.33*E-5
30 years/260d/8hrs
Assumption: cumulative
1 – (1-DR)260 x 30 = 4.33*E-5
DR = 5.55E-9
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Remediation cont’d
H2O2 Gas
1000ppm, 20 Pa for 20 min
Cycle reduction of 10E3
Target # spores in room: 0.000793 spores
Total # of cycles needed: ~1.5
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Number of spores in room as a function of remediation time
Time (min) # Spores in Room
0 5.00E+05
20 500
40 0.5
60 0.0005
80 0.0000005
100 5E-10
120 5E-13
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Number of spores in room as a function of remediation time
1.00E-13
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
0 20 40 60 80 100 120
Time (minutes)
Nu
mb
er
of
sp
ore
s in
ro
om
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Communication
Avoid disparities in treatment on the basis of race or social class
Tell the public What is anthrax? What are the symptoms? How is it transmitted? How can infection be prevented? How is anthrax treated? How likely a harmful biological or chemical substance in
the mail? What should people do if receiving an Anthrax threat by
mail?
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Communication cont’d
Avoid frequent changes to recommendations lack of significant prior experience with anthrax
Inform public what has been done & what will be done to secure their safety in the future
To treat the public with respect, listen to their opinion and make them decision making partners.
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Questions???
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