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Prioritizing risks and uncertainties from intentional release of selected Category A pathogens.

Hong T, Gurian PL, Huang Y, Haas CN - PLoS ONE (2012)

Bottom Line: Results indicate that when pathogens are released into the air, risk from inhalation is the main component of the overall risk, while risk from ingestion (dermal contact for B. anthracis) is the main component of the overall risk when pathogens are present on surfaces.A Monte Carlo uncertainty analysis is conducted and input-output correlations used to identify important parameter uncertainties.An approach is proposed for integrating these quantitative assessments of parameter uncertainty with broader, qualitative considerations to identify future research priorities.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil, Architectural, and Environmental Engineering, Drexel University, Philadelphia, Pennsylvania, United States of America. hongtao510@gmail.com

ABSTRACT
This paper synthesizes available information on five Category A pathogens (Bacillus anthracis, Yersinia pestis, Francisella tularensis, Variola major and Lassa) to develop quantitative guidelines for how environmental pathogen concentrations may be related to human health risk in an indoor environment. An integrated model of environmental transport and human health exposure to biological pathogens is constructed which 1) includes the effects of environmental attenuation, 2) considers fomite contact exposure as well as inhalational exposure, and 3) includes an uncertainty analysis to identify key input uncertainties, which may inform future research directions. The findings provide a framework for developing the many different environmental standards that are needed for making risk-informed response decisions, such as when prophylactic antibiotics should be distributed, and whether or not a contaminated area should be cleaned up. The approach is based on the assumption of uniform mixing in environmental compartments and is thus applicable to areas sufficiently removed in time and space from the initial release that mixing has produced relatively uniform concentrations. Results indicate that when pathogens are released into the air, risk from inhalation is the main component of the overall risk, while risk from ingestion (dermal contact for B. anthracis) is the main component of the overall risk when pathogens are present on surfaces. Concentrations sampled from untracked floor, walls and the filter of heating ventilation and air conditioning (HVAC) system are proposed as indicators of previous exposure risk, while samples taken from touched surfaces are proposed as indicators of future risk if the building is reoccupied. A Monte Carlo uncertainty analysis is conducted and input-output correlations used to identify important parameter uncertainties. An approach is proposed for integrating these quantitative assessments of parameter uncertainty with broader, qualitative considerations to identify future research priorities.

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Risk and uncertainty for different pathogens associated with an aerosol release over 8 hours (retrospective scenario) and with a surface release over an infinite time (prospective scenario).Medians shown in red, 1st and 3rd quartiles in blue. For input uncertainty distributions see Tables 1–2 of the main text and Information S2, table 2. (1. B. anthracis, 2. Y. pestis, 3. F. tularensis, 4. Variola major, and 5. Lassa).
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pone-0032732-g008: Risk and uncertainty for different pathogens associated with an aerosol release over 8 hours (retrospective scenario) and with a surface release over an infinite time (prospective scenario).Medians shown in red, 1st and 3rd quartiles in blue. For input uncertainty distributions see Tables 1–2 of the main text and Information S2, table 2. (1. B. anthracis, 2. Y. pestis, 3. F. tularensis, 4. Variola major, and 5. Lassa).

Mentions: Another objective of this study is to compare risk and uncertainties across different pathogens. The development of explicit formulae for exposure, that is Equations 24 and 25a(b), greatly simplifies uncertainty analysis. Using the input distributions listed in Table 1 and Table 2 with Equations 24 and 25a(b), a Monte Carlo analysis was carried out using to propagate uncertainties in input parameters through to uncertainties in risks for different pathogens. Results from retrospective and prospective scenarios are presented in the form of box plots (Figure 8). The relative risk presented by different pathogens in an air release are largely determined by their dose-response parameters, because the exposure duration in air is limited by the particle deposition rate (which is the same across different pathogens) rather than the decay rate. However, air decay rate does have an impact, when decay is rapid enough to occur over the time scale during which particulates are typically suspended (minutes to hours depending on the diameter of the particles) which is the case for Y. pestis, F. tularensis, and Lassa.,The relative risks for different pathogens in a surface release are affected by both fomite decay rates and dose-response parameters. In general the risk from releasing the same amount of pathogens can be ranked as Lassa, F. tularensis, Y. Pestis, B. anthracis, and Variola major (in decreasing order). This analysis does not include secondary transmission risks (which may be particularly important for all but B. anthracis and F. tularensis[34]) and as such does not capture a critical component of risk for pathogens, such as Variola major, which are subject to secondary transmission. Instead it addresses the question as to which pathogens are subject to the greatest uncertainty in setting surface concentration standards for primary exposure. Uncertainties presented by Lassa are highest across most of the cases (extending over roughly an order of magnitude), indicating that this organism may be a priority for further study (pending consideration of factors such as its likely use in an attack).


Prioritizing risks and uncertainties from intentional release of selected Category A pathogens.

Hong T, Gurian PL, Huang Y, Haas CN - PLoS ONE (2012)

Risk and uncertainty for different pathogens associated with an aerosol release over 8 hours (retrospective scenario) and with a surface release over an infinite time (prospective scenario).Medians shown in red, 1st and 3rd quartiles in blue. For input uncertainty distributions see Tables 1–2 of the main text and Information S2, table 2. (1. B. anthracis, 2. Y. pestis, 3. F. tularensis, 4. Variola major, and 5. Lassa).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3295774&req=5

pone-0032732-g008: Risk and uncertainty for different pathogens associated with an aerosol release over 8 hours (retrospective scenario) and with a surface release over an infinite time (prospective scenario).Medians shown in red, 1st and 3rd quartiles in blue. For input uncertainty distributions see Tables 1–2 of the main text and Information S2, table 2. (1. B. anthracis, 2. Y. pestis, 3. F. tularensis, 4. Variola major, and 5. Lassa).
Mentions: Another objective of this study is to compare risk and uncertainties across different pathogens. The development of explicit formulae for exposure, that is Equations 24 and 25a(b), greatly simplifies uncertainty analysis. Using the input distributions listed in Table 1 and Table 2 with Equations 24 and 25a(b), a Monte Carlo analysis was carried out using to propagate uncertainties in input parameters through to uncertainties in risks for different pathogens. Results from retrospective and prospective scenarios are presented in the form of box plots (Figure 8). The relative risk presented by different pathogens in an air release are largely determined by their dose-response parameters, because the exposure duration in air is limited by the particle deposition rate (which is the same across different pathogens) rather than the decay rate. However, air decay rate does have an impact, when decay is rapid enough to occur over the time scale during which particulates are typically suspended (minutes to hours depending on the diameter of the particles) which is the case for Y. pestis, F. tularensis, and Lassa.,The relative risks for different pathogens in a surface release are affected by both fomite decay rates and dose-response parameters. In general the risk from releasing the same amount of pathogens can be ranked as Lassa, F. tularensis, Y. Pestis, B. anthracis, and Variola major (in decreasing order). This analysis does not include secondary transmission risks (which may be particularly important for all but B. anthracis and F. tularensis[34]) and as such does not capture a critical component of risk for pathogens, such as Variola major, which are subject to secondary transmission. Instead it addresses the question as to which pathogens are subject to the greatest uncertainty in setting surface concentration standards for primary exposure. Uncertainties presented by Lassa are highest across most of the cases (extending over roughly an order of magnitude), indicating that this organism may be a priority for further study (pending consideration of factors such as its likely use in an attack).

Bottom Line: Results indicate that when pathogens are released into the air, risk from inhalation is the main component of the overall risk, while risk from ingestion (dermal contact for B. anthracis) is the main component of the overall risk when pathogens are present on surfaces.A Monte Carlo uncertainty analysis is conducted and input-output correlations used to identify important parameter uncertainties.An approach is proposed for integrating these quantitative assessments of parameter uncertainty with broader, qualitative considerations to identify future research priorities.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil, Architectural, and Environmental Engineering, Drexel University, Philadelphia, Pennsylvania, United States of America. hongtao510@gmail.com

ABSTRACT
This paper synthesizes available information on five Category A pathogens (Bacillus anthracis, Yersinia pestis, Francisella tularensis, Variola major and Lassa) to develop quantitative guidelines for how environmental pathogen concentrations may be related to human health risk in an indoor environment. An integrated model of environmental transport and human health exposure to biological pathogens is constructed which 1) includes the effects of environmental attenuation, 2) considers fomite contact exposure as well as inhalational exposure, and 3) includes an uncertainty analysis to identify key input uncertainties, which may inform future research directions. The findings provide a framework for developing the many different environmental standards that are needed for making risk-informed response decisions, such as when prophylactic antibiotics should be distributed, and whether or not a contaminated area should be cleaned up. The approach is based on the assumption of uniform mixing in environmental compartments and is thus applicable to areas sufficiently removed in time and space from the initial release that mixing has produced relatively uniform concentrations. Results indicate that when pathogens are released into the air, risk from inhalation is the main component of the overall risk, while risk from ingestion (dermal contact for B. anthracis) is the main component of the overall risk when pathogens are present on surfaces. Concentrations sampled from untracked floor, walls and the filter of heating ventilation and air conditioning (HVAC) system are proposed as indicators of previous exposure risk, while samples taken from touched surfaces are proposed as indicators of future risk if the building is reoccupied. A Monte Carlo uncertainty analysis is conducted and input-output correlations used to identify important parameter uncertainties. An approach is proposed for integrating these quantitative assessments of parameter uncertainty with broader, qualitative considerations to identify future research priorities.

Show MeSH
Related in: MedlinePlus