Modeling Urban Atmospheric Anthrax Spores Dispersion: Assessment of Health Impacts and Policy Implications

PurposeTo model atmospheric dispersion of weapon grade anthrax spores over an urban region using a mass transit system (subway) as a delivery system. IntroductionThe accessibility and carrying capacity of mass transit system (s) makes it an attractive target for terrorists. There are multiple, historical accounts of terrorists attacks involving transit systems. Metropolitan underground transportation rail systems (subways) are of special interest because of a potential harm to a large number of commuters and damage to the transportation infrastructure. MethodsWe assumed that multiple release points of anthrax spores within the National Capital Region (NCR-Washington, District of Columbia) METRO rail system will result in the escape of the spores into the atmosphere. Potential factors affecting atmospheric dispersion of spores and the regional infrastructure were the subject of literature searches, modeling exercises and expert reviews. A Geographic Information System (GIS) and the Operational Multiscale Environment Model with Grid Adaptivity (OMEGA) were used to model the affected area. ResultsThe GIS together with the OMEGA software programs characterized the extent of the ground footprint and provided the number of the NCR residential, businesses and health care infrastructure under the plume at 120 minutes after the release. It was concluded that the maximum environmental and health impacts would occur if the spores were released in the early morning during the summer months (low humidity and ultra-violet radiation). This assumption was based on the analysis of the weather patterns and prevailing winds in the NCR. ConclusionsThe atmospheric dispersion model superimposed over the regional GIS suggests that the extent of the affected infrastructure will be negligible. However it has the potential to disrupt the functioning of the mass transit system, affect serviced residential areas, commercial and/or federal facilities. While the number of affected medical and other facilities will be minimal, a significant number of commuters and resident will be exposed to the spores and overload the existing health care infrastructure. Policy implicationsAdopting a set of realistic threats assessment tools using GIS and atmospheric modeling, and addressing risk reduction strategies such as deploying real time biological agents monitoring sensors, can significantly improve the security of metropolitan communities served by interconnected mass transport systems. Field testing to validate our modeling assumptions and results will help with the training of disaster response teams, health care providers, transportation system operators and improve passengers' safety. Limitations This study has not been validated by actual field test data and as such is hypothetical and subject to a significant bias. Assumption of a release of a large amount (several kilograms) of anthrax spores undetected might be unrealistic based on existing physical surveillance and security practices. Patterns of spores' dispersion into fixed structures serviced by the subway system were not modeled in this research. The dispersion model does not take into account the progressive reduction of the number of anthrax spores as a function of the distance from the release source.