Fate and transport of viable bacillus anthracis simulant spores in ambient air during a large outdoor decontamination field exercise

ABSTRACT

The Wide Area Demonstration (WAD) was a field exercise conducted under the U.S. EPA’s Analysis of Coastal Operational Resiliency program, in conjunction with the U.S. Department of Homeland Security and the U.S. Coast Guard. The purpose of the WAD was to operationalize at field scale aspects of remediation activities that would occur following an outdoor release of Bacillus anthracis spores, including sampling and analysis, decontamination, data management, and waste management. The WAD was conducted in May 2022 at Fort Walker (formerly known as Fort A.P. Hill) and utilized Bacillus atrophaeus as a benign simulant for B. anthracis. B. atrophaeus spores were inoculated onto the study area at the beginning of the study, and air samples were collected daily during each of the different phases of the WAD using Dry Filter Units (DFUs). Ten DFU air samplers were placed at the perimeter of the study area to collect bioaerosols onto two parallel 47-mm diameter polyester felt filters, which were then subsequently analyzed in a microbiological laboratory for the quantification of B. atrophaeus. The study demonstrated the use of DFUs as a rugged and robust bioaerosol collection device. The results indicated that the highest B. atrophaeus spore air concentrations (up to ~ 5 colony forming units/m³) occurred at the beginning of the demonstration (e.g. during inoculation and characterization sampling phases) and generally downwind from the test site, suggesting transport of the spores was occurring from the study area. Very few B. atrophaeus spores were detected in the air after several weeks and following decontamination of exterior surfaces, thus providing an indication of the site decontamination procedures’ effectiveness. No B. atrophaeus spores were detected in any of the blank or background samples.

Implications

Following an incident involving a release of Bacillus anthracis spores or other biological threat agent into the outdoor environment, understanding the factors that may affect the bioagent’s fate and transport can help predict viable contaminant spread via the ambient air. This article provides scientific data for the first time on ambient air concentrations of bacterial spores over time and location during different phases of a field test in which Bacillus atrophaeus (surrogate for B. anthracis) spores were released outdoors as part of a full-scale study on sampling and decontamination in an urban environment. This study advances the knowledge related to the fate and transport of bacterial spores (such as those causing anthrax disease) as an aerosol in the outdoor environment over the course of three weeks in a mock urban environment and has exposure and health risk implications. The highest spore air concentrations occurred at the beginning of the study (e.g. during inoculation of surfaces and characterization sampling), and in the downwind direction, but diminished over time; few B. atrophaeus spores were detected in the air after several weeks and following decontamination. Therefore, in an actual incident, potential reaerosolization of the microorganism and subsequent transport in the air during surface sampling and remediation efforts should be considered for determining exclusion zone locations and estimating potential risk to neighboring communities. The data also provide evidence suggesting that the large-scale decontamination of outdoor surfaces may reduce air concentrations of the bioagent, which is important since exposure of B. anthracis via inhalation is a primary concern.

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Supplemental material

Supplemental data for this paper can be accessed on the publisher’s website.

Acknowledgements

The authors would like to thank the following people for their support and assistance throughout the project:

JTI: Tim Chamberlain and Jonathan Sawyer helped with sample kit preparation and Brian Ford, Lesley Mendez-Sandoval, and Rachael Baartmans processed the samples and recorded the data.

EPA Office of Research and Development: Lukas Oudejans, John Archer, and Paul Lemieux

US EPA personnel DFU sampling teams: Duane Newell, Ray Ledbetter, Jeff Szabo, Elise Jakabhazy

Consolidated Safety Services: Neil Daniel and Anne Busher

DHS: Don Bansleben and Andrea Wiggins; Jane Tang (DHS contractor)

USCG: Emile Benard

Weston Solutions: Lawrence Campagna

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

In general US EPA datasets may be found here: https://catalog.data.gov/organization/epa-gov. And specifically for this project, underlying raw data (e.g., microbiological plate counts) may be found here once the journal article is published: https://doi.org/10.23719/1529833.

Additional information

Funding

This study was partially funded through the Analysis for Coastal Operational Resiliency (AnCOR) program by the U.S. Department of Homeland Security Science and Technology Directorate (DHS S&T) under an interagency agreement (EPA No. RW- RW-070-95937001; DHS S&T 70RSAT18KPM000084). This report has been peer and administratively reviewed and has been approved for publication. The views expressed in this report are those of the authors and do not necessarily reflect the views or policies of the Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use of a specific product. The contents are solely the responsibility of the authors and do not necessarily represent the official views of S&T, DHS, or the United States Government.