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Risk Assessment: Release of Anthrax in an IRS Building

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. Outline. What is anthrax? Case Study Scenario Transport of Particles Dose Response Exposure Assessment Decision tree

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Risk Assessment: Release of Anthrax in an IRS Building

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  1. 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.

  2. Outline • What is anthrax? • Case Study Scenario • Transport of Particles • Dose Response • Exposure Assessment • Decision tree • Acceptable risk

  3. Outline cont’d • Sampling • Sites • Recovery Protocols • Detection Methods • Stakeholders • Remediation • Decontamination Procedure (explain method and acceptable limit

  4. Problem

  5. 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%

  6. Weaponized Anthrax Spores particle of zinc sulfide coated with silica. The zinc sulfide particle is about 2 microns across (similar in size to an anthrax spore), and the silica particles are about 100 nanometers http://cryptome.org/anthrax-powder.jpg

  7. Aerosolized Anthrax Radiographic examination of the chest often reveals characteristic mediastinal widening, indicative of hemorrhagic mediastinitis http://www.youtube.com/watch?v=WNRgLkjaRlY

  8. 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

  9. 10 feet 10 feet 10 feet 10 feet ZONE 4 ZONE 3 ZONE 2 ZONE 1 Transport Zones Scenario window Air flow Air Vent Break Area with chairs Plant Air Vent Coffee 30 feet wide 13 feet high Air Vent Air Vent Printer& Copier Plant 40 feet Not-to-scale

  10. 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

  11. Particle concentration Range reaching each Zone during 1 Air Turnover 1.00E+08 ZONE 4 ZONE 1 Instant ZONE 2 ZONE 3 9.00E+07 8.00E+07 7.00E+07 Receives Max Concentration spores 6.00E+07 diluted in room volume 5.00E+07 SENIOR MANAGER 4.00E+07 1e10 colonies - 9e7 3.00E+07 colonies 2.00E+07 1.00E+07 0.00E+00 0.00 0.00 2.63 5.26 7.89 Explosion Zone

  12. 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

  13. Dose-Response: Model • P(d) = 1/100 • d=1075-1813 spores • P(d) = 1/10,000 • d=11-18 spores Bartrand et al. 2008

  14. 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

  15. 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)

  16. 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

  17. Initial exposure risk results ‘k’ contributed 20% of the variation; Inhalation rate contributed 80% of the variation. There were 1000 Monte Carlo trials.

  18. $6milion(VSL) +$52 Yes q=80%p Death Yes Prophylaxis byDoxycycline $52 No 1-q=1-80%p No 1-p=10% $0 Death No Yes p=90% $6milion(VSL) Decision Tree

  19. 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

  20. CLINICAL SYMPTOMS / TRANSMISSION ROUTE Fonte: WHO,2007; Staples, 2006

  21. D.L.=12 CFU/cm2 (4 papers-Surfaces) 40% 93% D.L.=430 CFU/mL (18 papers-Instrument) Surface Sampling Method

  22. D.L.=50 spores/L (2 papers) 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

  23. 10 feet 10 feet 10 feet 10 feet Plant Plant Sampling Zones 30 million surface samples (95% confidence) window Air flow Break Area with chairs Air Vent Air Vent Coffee Senior Manager 30 feet Air Vent Air Vent Printer& Copier 40 feet =air sampling =surface sampling Not-to-scale

  24. Who Cares???

  25. 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

  26. Remediation • Uses: • decontamination • Lab & medical equipment • Pharmaceutical facilities • Hospital rooms • Animal holding rooms

  27. 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

  28. 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

  29. Number of spores in room as a function of remediation time

  30. 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?

  31. 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.

  32. Questions???

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