Development of a comparative risk ranking system for agents posing a bioterrorism threat to human or animal populations.

Various systems for prioritizing biological agents with respect to their applicability as biological weapons are available, ranging from qualitative to (semi)quantitative approaches. This research aimed at generating a generic risk ranking system applicable to human and animal pathogenic agents based on scientific information. Criteria were evaluated and clustered to create a criteria list. Considering availability of data, a number of 28 criteria separated by content were identified that can be classified in 11 thematic areas or categories. Relevant categories contributing to probability were historical aspects, accessibility, production efforts, and possible paths for dispersion. Categories associated with impact are dealing with containment measures, availability of diagnostics, preventive and treatment measures in human and animal populations, impact on society, human and veterinary public health, and economic and ecological consequences. To allow data-based scoring, each criterion was described by at least 1 measure that allows the assignment of values. These values constitute quantities, ranges, or facts that are as explicit and precise as possible. The consideration of minimum and maximum values that can occur due to natural variations and that are often described in the literature led to the development of minimum and maximum criteria and consequently category scores. Missing or incomplete data, and uncertainty resulting therefrom, were integrated into the scheme via a cautious (but not overcautious) approach. The visualization technique that was used allows the description and illustration of uncertainty on the level of probability and impact. The developed risk ranking system was evaluated by assessing the risk originating from the bioterrorism threat of the animal pathogen bluetongue virus, the human pathogen Enterohemorrhagic Escherichia coli O157:H7, the zoonotic Bacillus anthracis, and Botulinum neurotoxin.