OSI Delhi Summer 2014 Case Study
Responding to Bioterrorism
Developed by Heather Galada, Patricia Gallagher
Kyle Griffith, Patrick Gurian, Michael Hamilton, Laura Hasiuk, Tao Hong,
Victoria Young
OBJECTIVES
Examine the risks posed by a release of 1 gram of Bacillus anthracis spores in the City of
Philadelphia. Evaluate risk management options, including use of antibiotic prophylaxis,
vaccination, evacuation, and remediation of contaminated environments.
Approach
Consider the following scenario:
An individual walks into Love Park in Philadelphia, Pennsylvania, USA, shouts “You are
all going to die!” and releases 1 gram of Bacillus anthracis spores, consisting of 90% 10
uM particles, 5% 5 uM particles, 4% 3uM particles, and 1% 1 uM particles. The release
occurs at a height of 2.4 meters, the wind is from the west at 4 m/s, and atmospheric
buoyancy conditions are neutral.
1. Develop and describe a Risk Framework (problem, hazard(s), dose-response,
exposure pathways, individual and population risk characterization)
2. Identify data & data needs
3. Identify techniques & models
4. Identify assumptions
5. Undertake a quantitative risk assessment
6. Identify data gaps
7. Develop conclusions on risk
8. Concisely communicate results and recommendations from the risk assessment
The following steps are suggested to implement these steps in this context:
1. Begin by considering the dispersion of the spores using a Gaussian Puff model
The puff model is defined by the following equation:
Cr ( xr , yr , zr , t )
  y 2    ( zr  H e ) 2 
  ( xr  Ut) 2 
  ( z r  H e ) 2 
 r exp 





exp
exp

exp
2
2
2





 2 2  
(2 )1.5 x y z
2 x
2 z
2 z





 y  
Q
where
Cr
= concentration at receptor, spores/m3
xr, yr, zr
= Cartesian coordinates downwind of the puff, m
Q
= emission rate, spores
t
= time since release, s
U
= wind speed, m/s
He
= height of puff centerline, m
σx, σy, σz=standard deviations of the concentration distribution x-, y-, z-directions, m
Suggested parameters are shown in Table 1.
Table 1. Model inputs
MODEL INPUTS
CONSTANTS
Base (variations)
1.3E12 (1.3E11, 1.3E13)
4 (2, 6.7)
2.4384
2.21
3.33E-4 m3/sec
7.43E-6 (9.10E-7, 7.10E-5)
C (A, G)
Q (spores)
U (m/sec)
He (m)
Solar Radiation
Inhalation rate:
R value
Stability Class
Time Step (sec onds)
Exposure Time (sec onds)
Sourc e Height (m)
Inhalation Height Range (m)
300
1800
2.4384
1.17 - 1.67
Dispersion Parameters for Instantaneous Releases
Dispersion Parameter
σy
σz
Stability
Equation
(x in meters)
Unstable
Neutral
Very stable
Unstable
Neutral
Very stable
0.14x 0 .9 2
0.06x 0 .9 2
0.02x 0 .8 9
0.53x 0 .7 3
0.15x 0 .7 0
0.05x 0 .6 1
Sourc e for dispersion parameters: Islitzer and Slade 1968.
1) Based on the concentration profile over time, estimate the dose to humans (see
QMRA Wiki for dose response information) and the deposition of the spores onto
surfaces (the ground, walls of buildings, etc., see Hong et al. 2010 for deposition
rate information).
2) Indoor exposure may be modeled with a completely mixed compartment model
dMin/dt = QCout -QCin - kdepositon VCin
where Min is the mass in the indoor air, V is the volume of the indoor space, Cin
is the indoor air concentration, and kdeposition is the deposition rate of the
spores. The solution to the above differential equation will give the concentration
of spores over time. However, Hong and Gurian (2012 see Figure S2 in
Supporting Information) have already worked out typical mass distributions of
spores by compartment so you can simply take the amount of spores that reached
the indoor area:
Min = ∑(1-f) Q Couti
where Couti is the outdoor concentration at time step i that is obtained from the
Gaussian puff model and f is the fraction removed by an HVAC filter (if present)
or that is deposited in cracks (if infiltration through cracks is a transport pathway
of concern). The principle of superposition applies for first order environmental
transport and reaction processes. This principle allows concentrations from
different sources to be modeled independently and the resulting concentration
profiles summed. You can combine masses that entered the building at different
time steps into a single release and obtain the correct net deposition to different
surfaces. Then you can apportion this mass deposition among different indoor
surfaces according to the rough percentages given by Hong et al. (2012). These
surface concentrations can be mapped to risk levels using the figures and tables in
Hong et al. (2010) and the actions appropriate to different risk levels identified
using a benefit-cost framework such as that of Mitchell-Blackwood et al. (2011)
or Hamilton et al. (under review).
OUTPUTS
Try to identify which actions should be taken in which regions to respond to this risk. For
example, at what distance downwind should no action be taken?
Document your case study using the report template provided on the QMRA Wiki and
develop a 20-minute oral presentation on your results. Specific items that should be
addressed in each section of the template are provided at:
http://qmrawiki.msu.edu/index.php?title=Case_Studies#tab=Case_Study_Criteria
References
Hamilton et al. under review “Risk-based decision making for reoccupation of
contaminated areas following a wide-area anthrax release”.
Hong, T. and P.L. Gurian. 2012. “Characterizing Bioaerosol Risk from Environmental
Sampling” Environmental Science and Technology, 46(12):6714-6722.
Hong, T., P.L. Gurian, N.F. Dudley Ward. 2010. “Setting Risk-Informed Environmental
Standards for Bacillus Anthracis Spores,” Risk Analysis, 30(10):1602-1622.
Islitzer, N. F. and Slade, D. H. 1968. Meteorology and Atomic Energy, D. H. Slade, Ed.,
U. S. Atomic Energy Commission, Office of Information Services.
Mitchell-Blackwood, J., P.L. Gurian, C. O’Donnell. 2011. “Finding Risk-based
Switchover Points for Response Decisions for Environmental Exposure to Bacillus
anthracis,” Human and Ecological Risk Assessment, 17(2):489-509.