Characterizing Bioaerosol Risk from Environmental Sampling

In the aftermath of a release of microbiological agents, environmental sampling must be conducted to characterize the release sufficiently so that mathematical models can then be used to predict the subsequent dispersion and human health risks. Because both the dose–response and environmental transport of aerosolized microbiological agents are functions of the effective aerodynamic diameter of the particles, environmental assessments should consider not only the total amount of agents but also the size distributions of the aerosolized particles. However, typical surface sampling cannot readily distinguish among different size particles. This study evaluates different approaches to estimating risk from measurements of microorganisms deposited on surfaces after an aerosol release. For various combinations of sampling surfaces, size fractions, HVAC operating conditions, size distributions of release spores, uncertainties in surface measurements, and the accuracy of model predictions are tested in order to assess how much detail can realistically be identified from surface sampling results. The recommended modeling and sampling scheme is one choosing 3, 5, and 10 μm diameter particles as identification targets and taking samples from untracked floor, wall, and the HVAC filter. This scheme provides reasonably accurate, but somewhat conservative, estimates of risk across a range of different scenarios. Performance of the recommended sampling scheme is tested by using data from a large-scale field test as a case study. Sample sizes of 10–25 in each homogeneously mixed environmental compartment are sufficient to develop order of magnitude estimates of risk. Larger sample sizes have little benefit unless uncertainties in sample recoveries can be reduced

Characterization of a bifunctional APAC agent capable of homing to active platelets.

<p>(A) Binding assay of APAC to platelets. (a) resting mouse platelets; (b) ADP-stimulated mouse platelets; (c) resting human platelets; (d) ADP-stimulated human platelets, respectively. (B) Binding assay of APAC versus A11 to activated human platelets determined by flow cytometry. Data were presented as mean ±SD (n = 3). (C) Effect of APAC on platelet fragmentation. Bars labeled 2, 3 and 4 after 1 refer to serial doubling dilutions of 1∶2–1∶16 respectively (0.1 µM APAC), n = 4, SD is given. (D) Dissolution of ex vivo collagen-induced platelet aggregates with APAC. Data and SD are given for 3 separate experiments at 0.1 µM reagent in which each time point represents 5 measurements.</p

Synergy of APAC and SLK on ex vivo platelet aggregate dissolution and platelet-rich clot lysis.

<p>(A) Platelet aggregates were prepared as described above. Black bars refer to platelet aggregate size at zero time. The 3 companion hatched bars refer to platelet aggregate size at 2 hours. Concentration of SLK and APAC was at 0.025 µM. SLK+APAC double hatched bar refers to final SLK and APAC concentration at 0.025 µM each. (B) Platelet-rich clots were formed on the wells of ELISA plate. The clots were treated with 0.025 µM Ctl scFv (13CG2) or SLK or APAC or SLK+APAC. SLK+APAC refer to final SLK and APAC concentration at 0.025 µM each. The relative clot turbidity was calculated by detecting the decrease of the absorbance at OD405. The mean±SD. came from 3 separate experiments. Each time point represents 5 measurements.</p

Generation of a bifunctional APAC capable of homing to active platelets.

<p>(A) Schematic diagram describing cloning strategy for the fusion construct. (B) Plasmid Construct. (C) 12% SDS-PAGE analysis of five aliquots of purified fusion protein (∼60 KD) with Ni-column following induction by 1 mM IPTG.</p

Best Fit Dose-Response Model.

a<p>In exponential dose-response model, R is used as virulence coefficient, while in beta-Poisson dose-response model, the ratio of α/β is used as virulence coefficient.</p>b<p>The distributions are fitted to bootstrap samples of dose response parameters using @RISK <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone.0032732-RISK1" target="_blank">[62]</a>.</p>c<p>The intestinal risk is replaced by cutaneous risk since the fractions of inhalational anthrax and cutaneous anthrax were the same in the 2001 anthrax letters attacks <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone.0032732-Lesperance1" target="_blank">[6]</a>.</p>d<p>The data for 2.1 µm particles are used.</p>e<p>The data for 4.5 µm or less in diameter are used.</p>f<p>The data for the age group of 5 days and above are used.</p

The ratio of accumulative inhalation and ingestion exposure.

<p>The ratio of accumulative inhalation and ingestion exposure.</p

Equipment detection limit associated risk^*.

*<p>It is assumed that the detection limit is 10 organisms which comes from sampling a 0.09 m² surface with the pathogen concentration 292 organisms per m² and the recovery rate is 0.38 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone.0032732-Hong2" target="_blank">[12]</a>.</p

Cumulative retrospective risks associated with <i>Y. pestis</i> HVAC concentrations after an aerosol release.

<p>Cumulative retrospective risks associated with <i>Y. pestis</i> HVAC concentrations after an aerosol release.</p

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).

<p>Medians shown in red, 1^st and 3^rd quartiles in blue. For input uncertainty distributions see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone-0032732-t001" target="_blank">Tables 1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone-0032732-t002" target="_blank">2</a> of the main text and Information S2, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032732#pone-0032732-t002" target="_blank">table 2</a>. (1. <i>B. anthracis</i>, 2. <i>Y. pestis</i>, 3. <i>F. tularensis</i>, 4. <i>Variola major</i>, and 5. Lassa).</p

Retrospective risks associated with <i>B. anthracis</i> HVAC concentrations after an aerosol release.

<p>Retrospective risks associated with <i>B. anthracis</i> HVAC concentrations after an aerosol release.</p