Updating aB. anthracisRisk Model with Field Data from a Bioterrorism Incident

Abstract

In this study, a Bayesian framework was applied to update a model of pathogen fate and transport in the indoor environment. Distributions for model parameters (e.g., release quantity of B. anthracis spores, risk of illness, spore setting velocity, resuspension rate, sample recovery efficiency, etc.) were updated by comparing model predictions with measurements of B. anthracis spores made after one of the 2001 anthrax letter attacks. The updating process, which was implemented by using Markov chain Monte Carlo (MCMC) methods, significantly reduced the uncertainties of inputs with uniformed prior estimates: total quantity of spores released, the amount of spores exiting the room, and risk to occupants. In contrast, uncertainties were not greatly reduced for inputs for which informed prior data were available: deposition rates, resuspension rates, and sample recovery efficiencies. This suggests that prior estimates of these quantities that were obtained from a review of the technical literature are consistent with the observed behavior of spores in an actual attack. Posterior estimates of mortality risk for people in the room, when the spores were released, are on the order of 0.01 to 0.1, which supports the decision to administer prophylactic antibiotics. Multivariate sensitivity analyses were conducted to assess how effective different measurements were at reducing uncertainty in the estimated risk for the prior scenario. This analysis revealed that if the size distribution of the released particulates is known, then environmental sampling can be limited to accurately characterizing floor concentrations; otherwise, samples from multiple locations, as well as particulate and building air circulation parameters, need to be measured.

Considerations for estimating microbial environmental data concentrations collected from a field setting

“… 61 Knowledge of the distribution of the size of the particles that have been released help reduce uncertainty in the sample estimate of estimate of risk. 62 Further, data collected in a real-world event could differ from data collected in field research.…”

“… 25 Sego et al 121 have proposed a sampling model using Bayesian techniques which combines judgement samples taken in high risk areas and random sampling in low-risk areas and provide an estimate of the number of samples needed to provide confidence in decisions regarding clearing a room. Hong et al 62 have also used Bayesian techniques to integrate fate, transport, and risk assessment models. From the results of their study, they have recommended that environmental sampling can be limited to determination of concentration of spores on the floor if the particle size distribution is known.…”

“…However, if the particle size distribution is not known, then multiple sample locations and an account of air circulation and particle density measurements would also be needed. 62 Stuart and Wilkening 61 have suggested the need to better understand degradation of agent viability and subsequent modeling of viability in different environments both before an event and after an event. In addition, establishment of a DQO process 24 for microbial agents is needed.…”

Dose‐Response Modeling for Inhalational Anthrax in Rabbits Following Single or Multiple Exposures

“…Since then, much research has been conducted and our understanding of the disease has improved significantly. However, one gap that remains is the ability to characterize the risk of disease following inhalation of a low dose of spores . Several low‐dose exposure scenarios are relevant to an aerosol attack with B. anthracis spores.…”

“…However, one gap that remains is the ability to characterize the risk of disease following inhalation of a low dose of spores. (7)(8)(9)(10)(11)(12)(13)(14)(15)(16) Several lowdose exposure scenarios are relevant to an aerosol attack with B. anthracis spores. One exposure scenario would be inhaling a single dose of spores within a short period of time (approximately 10-15 minutes), which would reflect an acute exposure that might be encountered during an attack.…”