A New Model of Bioterrorism Risk Assessment

Abstract

There has been an abundance of different bioterrorist attack scenarios and consequently an unclear biodefense strategy so far. We present a framework for bioterrorism risk assessment that we believe would be useful for policymakers and understandable without needing to be an expert in this field. We retrieved the Medline database via PubMed (from January 1987 to January 2009) and cross-referenced and reviewed the terms biological weapons, biological attacks, bioterror, bio(defense), bio(strategy) and epidemiologic models, and risk assessment. Additionally, we conducted an internet search with the same terms and strategy. We divided bioterrorist attacks into 3 categories: strategical (large-scale), operational (middle-scale), and tactical (small-scale). A bioterrorist attack is presented as a 4-component chain model, including perpetrators, agents, means of delivery, and targets. For any of these 4 components, we propose quantitative and qualitative risk assessment parameters. Here we present a simple scoring system within our model applied to the 2001 U.S. anthrax attacks.

A2008 Department of Homeland Security (DHS) announcement stated: “The threat posed by biological agents employed in a terrorist attack on the United States is arguably the most important homeland security challenge of our era. Even if there were fewer casualties, additional second-order consequences (including psychological, social, and economic effects) would dramatically compound the effects.”¹ In 2006, DHS completed its first Bioterrorism Risk Assessment, intended to be the foundation for DHS's subsequent biennial risk assessments, which were mandated by Homeland Security Presidential Directive 10 (HSPD-10). At the request of DHS, the National Research Council established the Committee on Methodological Improvements to the Department of Homeland Security's Biological Agent Risk Analysis to provide an independent, scientific peer review of the bioterrorism risk assessment.²

The Committee identified a number of fundamental problems with the bioterrorism risk assessment, ranging from the use of unnecessarily complicated probability models, to simplistic assumptions regarding the manner in which terrorist behavior should be modeled. The Committee also unanimously judged the bioterrorism risk assessment unsuitable for risk management.¹

Bioterrorist attacks have been so infrequent that we have limited data from which to draw. While data regarding targets and bioagent characteristics are available to a lesser or greater extent, information on bioterrorist intent is just about nonexistent. This data gap stems in part from the rarity of bioterrorist events. To illustrate, a search of the Center for Nonproliferation Studies (CNS) terrorism database, which is the largest unclassified one of its kind, revealed that biological agents were used by criminals or terrorists from 1900 to 2001 in 77 biological “events” (ie, episodes involving the deliberate use of a biological agent to harm people). Of these, just 4 post-1945 events generated more than 10 casualties.³

As the 9/11 attacks demonstrated, terrorists will design their attacks to exploit our vulnerabilities and attempt to achieve consequences that will meet their objectives. An analogy to the events of 9/11 might be useful here. If the bioterrorism risk assessment were to be used to characterize the threat of 9/11, experts would have assigned probabilities for Al-Qaeda to choose the World Trade Center towers as the target and planes as the weapon. These small probabilities, when multiplied by the number of deaths caused by such an attack, would have resulted in a very small number, and the risk of such attack would have been deemed insignificant. However, terrorists, our intelligent adversaries, did not assign probabilities to each of their choices. Terrorists are goal-oriented, resourceful adversaries who will, given the constraints they perceive, select the best agent and target to achieve their objectives.²

There is a wide range of bioterrorist attack scenarios, making it hardly possible to completely anticipate, prepare for, or educate for all bioterror situations.^4,5 The nature and scope of a deliberate epidemic following a biological attack will depend on many factors.^6,7 Preparing for a bioterrorist attack includes analyzing and coordinating information and events in the scientific, political, and social arenas. Sometimes such interactions result in erroneous conclusions and flawed interventions.⁸ The priorities of the scientific community are to improve biodefense, plan the resources, and reduce costs.⁹ We believe that the first step in this effort should be the development of an effective and universally applicable bioterrorism risk assessment model.

To bridge a “gap” of rarity of biological “events,” we propose a new bioterrorism risk assessment model starting from the minimum of necessary components. The first step in this effort is to systematize a complexity of 4 bioterrorist attack components: perpetrators, agents, means or media of delivery, and targets. We will introduce quantitative and qualitative parameters for all 4 components and the types of bioterrorist attack. As a second step, we apply the bioterrorism risk assessment to the 2001 anthrax attacks.

Methods

We reviewed the Medline database via PubMed from January 1987 to January 2009 and abstracts from major meetings on biological weapons held from 1992 to 2008, published in English. Articles were identified by cross-referencing terms: biological weapons, biological attacks, bioterror, biodefense, biostrategy, risk assessment, and epidemiologic models. Additionally, an internet search was conducted with the same terms and strategy.

Components and Parameters of a Biological Attack

Four components comprise a biological attack: perpetrators, agents, means or media of delivery, and targets. Qualitative parameters have specific characteristics, while quantitative parameters differ in the degree of characteristics (Table 1).

Table 1.

Components and parameters of a bioterrorist attack

Component	Qualitative Parameters	Quantitative Parameters
Perpetrator	Type of perpetrator (government institutions/organizations, terrorist groups, individuals)	Number of perpetrators
	Sophistication, motivation, ability, capacity	Distribution of perpetrators (accessibility to sources of agent and accessibility to the target)
	Intelligence/secrecy (global and local)
Agent	Type of agent (categories A, B, and C and emerging pathogens)	Accessibility to terrorists
		Amounts of the available agent
Means and media of delivery	Air	Munitions
	Food	Delivery systems
	Water	Dispersion systems
	Fomites
Target	Parameters of control:
	Intelligence/secrecy (global and local)	Number of people in the target
	Personal/individual control	Distribution of people in the target
	Control of media (air, food, and water)	Location of the target
	Control of fomites (office equipment, postal letters, etc.)
	Parameters of protection (physical, chemical, immunological)

Perpetrators

Qualitative Parameters

Three types of perpetrator exist: government organized and supported perpetrators (institutions and organizations), terrorist groups, and individuals. Today, the real threats are almost exclusively from terrorists or disaffected groups. Other qualitative parameters are sophistication and motivation.¹⁰ Highly sophisticated perpetrators use highly dangerous agents (category A agents or emerging agents), attack without suicidal intent, keep themselves unknown, and try to attack “hard” targets. Such perpetrator(s) carried out the U.S. anthrax attacks in 2001. Highly motivated perpetrators (mainly poor terrorists or fanatics with suicidal intent) will probably use the more available category B agents, allow themselves to be identified, and attack public targets (“soft” targets).

In the context of bioterrorism, infectious diseases are not only a public health issue but also an issue of national and international security. In the past, the essence of terrorism was to make a political statement through violence. The extent of violence was calculated to draw attention without alienating supporters or triggering a radical response from the authorities. In the postmodern or superterrorism, the aim is to maximize the number of casualties.¹¹ Intelligence presents the ability to get true and timely information on global and local levels related to a biological attack. Secrecy comprises the capacity to keep activities unobserved before an attack and to keep perpetrators unknown after the attack.

Quantitative Parameters

These include the number of perpetrators and their distribution. These parameters affect the accessibility of sources of infectious agents and their targets to bioterrorists.

Agents

Qualitative Parameters

There are 2 types of agents: biological agents and information as an agent (Figure 1).¹² Biological agents can transform to information as agent from the level of direct/biological target to the level of indirect/political target. The Centers for Disease Control and Prevention (CDC) classified critical biological agents into 3 major categories (A, B, C).¹³ The category A agents are: Variola major, Bacillus anthracis, Yersinia pestis, Clostridium botulinum toxin, Francisella tularensis, and Filoviruses and Arenaviruses related to Ebola and Marburg hemorrhagic fevers, Lassa fever, and Argentine hemorrhagic fever. Category B contains about 30 potential agents, including a wide variety of bacteria, viruses, protozoa, and toxins.¹⁴ These pathogens are attractive as potential bioweapons because they do not cause mass destruction and do not induce major public health consequences. Category C includes Nipah virus, Hantavirus, tickborne hemorrhagic fever viruses, tickborne encephalitis (TBE) virus complex, yellow fever, and multidrug-resistant tuberculosis (MDR-TB).

Figure 1.

Levels of a bioterrorist attack

Additionally, there are several emerging pathogens with the potential for bioterrorism: severe acute respiratory syndrome (SARS), pandemic and avian influenza, West Nile virus infection, and monkeypox virus infection. They represent a large threat throughout the world, because of geographical expansion and potential genetic manipulation. Their use, or even the threat of use, could cause widespread social disruption.

Biologic agents are also categorized as conventional and genetically modified agents.¹⁵ Traditional biological weapons include naturally occurring organisms or toxins, characterized by easy production, high toxicity, stability, and abundance of modes of transmission.^16,17 Conventional agents can be genetically modified, which makes them more virulent, resistant to antibiotics, able to produce toxins, and able to remain stable in aerosols or other media.¹⁸

Quantitative Parameters

Quantitative parameters of agents include the amount and distribution of the existing agents.¹⁹ Rapid research in the field of synthetic biology increases concerns about safety and security (eg, dual-use research), because, in theory, deadly organisms could be created in a laboratory setting.²⁰ Improved DNA synthesis means that microbial genomes can be built from scratch, bypassing the need to get hold of an actual organism. For example, in July 2002 researchers at the University of New York at Stony Brook reported that they had synthesized an infectious poliovirus using mail-ordered DNA.²¹ Many researchers use made-to-order components to re-engineer the genomes of bacteria or viruses to give them novel abilities. This implies that synthetic biology can be abused for bioterrorism purposes, which is hard to control.²² On the other hand, synthetic biology can be used to produce drugs and vaccines or sensors for detecting altered organisms in the environment.²³

The sources of biological agents are everywhere. Besides natural sources, there are more than 1,500 biological culture libraries and institutions worldwide with sample cultures.²⁴ Although their growth, purification, stabilization, and transmission requires specific technical capabilities, they are commercially available.²⁵

Media and Means of Delivery

Qualitative Parameter

The media of delivery could be air, food, or drinking water.^26,27

Quantitative Parameters

Technical equipment is needed to keep and transport agents. The means of delivery have 3 components: (1) munitions that carry, protect, and maintain the virulence of the payload during delivery; (2) a delivery system can range from a missile, a vehicle (aircraft, boat, automobile, or truck), an artillery shell, an expendable soldier or martyr, to everyday postal mail (fomites); (3) a dispersion system ensures dissemination of the payload at and around the target site among susceptible populations.²⁸

Targets

Qualitative Parameters

There are 2 types of targets: direct (biological) and indirect (political/economic). Biological or direct targets could be “hard” or “soft.” The U.S. anthrax attacks in 2001 comprised both types of attack: the Hart Senate Office Building in Washington, DC, was “hard,” and the U.S. Postal Service offices were “soft” targets. The estimated cost of decontaminating parts of the Hart building was $23 million (“hard” economic target). The economic impact of a biological attack involving potential exposure to anthrax was estimated at $26.2 billion/100,000 persons exposed (“soft” economic target). The cost and resources needed to decontaminate the environment should be added to this.²⁹ The airline industry worldwide lost $10 billion in 2003 because of SARS.³⁰

We propose 2 types of qualitative parameters: parameters of control and parameters of protection. Parameters of control comprise several categories: intelligence/secrecy (global and local); personal/individual control; control of media such as air, food, and water; and control of services/fomites, such as office equipment or postal letters.

Intelligence is a cornerstone of prevention. Information is provided using electronic surveillance methods, local intelligence systems, and observations of possible targets.³¹ Repeated visits by individuals or vehicles must be identified. The impact of secrecy has been evident in some recent incidents. Such an incident occurred in the aftermath of the 2001 anthrax letters. Although the U.S. Postal Service and the CDC knew that the Brentwood postal facility in Washington, DC, was contaminated, they waited for 4 days before closing the facility and treating workers with antibiotics. By that time, 1 worker had died of anthrax, another was close to death, and 2 were gravely ill. Another example is China in 2003, when the government denied the SARS epidemic for 6 weeks, causing international alarm and spread of the disease.³² These illustrate that government secrecy presents a persistent jeopardy, leaves the public in ignorance, and allows narrow-minded political agendas to undermine healthcare goals.

The highest standards of parameters of control must apply to “hard” targets. Personal control includes physical control of people (their health status) and behavioral control (CV reviewing, control of suspected behavior, control of contacts).

Control of water includes use of bottled water and permanent surveillance of central water supply systems. Food control should follow the principle “from the farm to the fork.”³³ Air conditioning systems should be developed and applied (biosensors).

Parameters of protection can be physical, chemical, or immunological. One form of physical protection of people is the advice to remain indoors in response to a biological attack alarm. This will simply prevent transmission of biological agents. Another example is the use of air conditioning systems, or systems of increasing air pressure in different parts of buildings.³⁴ Furthermore, UV radiation sources may be used as physical protection.

Chemical protection refers to use of antibiotics, which is a great logistical challenge, since it provides protection only against classic agents (eg, anthrax or plague) for as long as the available stocks last. Mass immunization programs require careful consideration to assess potential risks and benefits. A nationwide smallpox vaccination campaign, carried out in November 2002 in the U.S., was based on the idea of smallpox-infected Iraqis invading America. It resulted in 145 serious adverse events among civilians (eg, hospitalization, permanent disability, life-threatening illness, and at least 3 deaths).³⁵

Quantitative Parameters

Quantitative parameters are the number and distribution of people at a target and the location of a target. Since overcrowded targets are at highest risk, people must be advised to avoid them. Potential targets should be safely organized, well protected, located out of a dense urban area, and with easily accessed roads.

Types of Biological Attack

In our opinion, 3 types of biological attack might be identified, according to their scope, severity, and consequences: strategic, operational, and tactical (Figure 1).

Strategic Biological Attack

A strategic (large-scale) biological attack is the acquisition and use by an independent actor of a biological agent that has the capability to harm or kill people en masse. At a strategic level, biological weapons have some advantages over classical nuclear and chemical weapons. Because of that, a threat of biological weapons requires a different paradigm than for conventional terrorism or for attacks caused by other weapons of mass destruction.

Perpetrators

States' institutions, such as military forces, intelligence services, or well-funded and possibly state-supported organizations, can be perpetrators of strategic biological attacks. Terrorist groups may also use biological agents at the strategic level (more probably than nuclear and chemical weapons). If a small group has the technical capability to produce and disseminate biological weapon agents, then traditional nonproliferation and counterproliferation emphasis on state biowarfare programs might divert attention and resources from preventing biological weapons proliferation to non-state actors. A strategic attack includes only politically and ideologically motivated cases. Some bioterrorists want to avoid attribution for an attack; others want to claim credit for it, or at least want the authorities to recognize that a disease outbreak was deliberate and not of natural origin.

Preparations for a strategic biological warfare act are almost unremarkable. The period between deployment of a bioweapon and its effects is long, which gives terrorists a chance to escape. Strategic attack using viral respiratory bioagents (eg, influenza virus or SARS) is highly possible, and in such cases it would be difficult to distinguish between a natural disaster and a biological terrorist act. A clandestine biological attack with highly dangerous agents (eg, anthrax, smallpox, viral hemorrhagic fever) is hardly possible, since it might be detected more easily and more quickly.

Agents

Many infectious microorganisms could be obtained from natural sources, such as infected animals, patients, or contaminated soil (eg, anthrax spores). But since natural pathogens vary in virulence, many strains isolated from nature may have low virulence. Therefore, a terrorist must isolate many different strains before finding one sufficiently potent as a weapon. Considering the technical difficulties in obtaining virulent microorganisms from nature, terrorists may find it easier to steal well-characterized strains from a research laboratory, or to purchase the known pathogenic strains from a national culture collection or a commercial supplier. Between 1985 and 1989, the Iraqi government ordered virulent strains of anthrax and other pathogens from culture collections in France and the U.S., presumably for public health research—a purpose that was legal at the time and indeed approved by the Department of Commerce.^36,37 Respiratory agents are good candidates for strategic use because of their possibility for clandestine use, high dispersal, and high contagiousness.

Means and Media of Delivery

Means of delivery depend on the characteristics of the agent. The only means of delivery of respiratory agents for strategic and clandestine use is airplanes. The Congressional Office of Technology Assessment estimated that the aerosolized release of 100 kg of anthrax spores upwind of Washington, DC, could result in approximately 130,000 to 3 million deaths.³⁸ It is obvious that a jet plane could deliver a great amount of biological agent.³⁹

Other means of delivery are food and water. Centralized food production and water supply systems in many developed countries increase vulnerability to foodborne^40,41 and waterborne pathogens (botulism and anthrax).⁴² Multiple means of delivery are also possible; for example, anthrax can be an airborne or foodborne agent.

Targets

Strategic use encompasses large territories and large populations, by killing people and/or damaging public health. Biological attacks cause 2 types of epidemics: epidemics of infectious disease and epidemics of fear and panic.¹² An epidemic (or pandemic) of fear and panic multiplies the economic damage (eg, losses in tourism, investment, and export). Today, the main objective of bioterrorists is to propagate fear, anxiety, uncertainty, and depression within the population, induce mistrust of government, inflict economic damage, and disrupt travel and commerce. The cause of physical disease is the second important objective. The ultimate goal of bioterrorist attacks is political consequences.

Operational Level

The operational level of the use of biological weapons presents a mixture of strategic and tactical levels of deploying bioweapons. This is the most probable type of biological attack in general. Dimensions of an affected area are not so large, only a city or town or a municipality.

Perpetrators

Military/intelligence services prefer to attack military/intelligence targets at the operational level (eg, military and related industries, military/intelligence bases, camps, training centers, headquarters). This is a clandestine type of attack. By contrast, terrorist groups may also attack military targets, but they prefer to propagate psychological effects (fear and panic), incite political consequences, and show off their accomplishments. Their priorities are civilian targets. Furthermore, they want to prove that authorities are unable to protect themselves and civilians (direct political pressure). Disaffected individuals may attack vulnerable populations (eg, hospital patients, children at schools) and vulnerable settings (eg, water supply systems, food production facilities). Terrorists may use certain vulnerable groups to test or to improve their biological weapons.

Agents

The category A agents, some emerging agents, and some kinds of category B bioagents could be used. For operational level, both waterborne and foodborne agents might be used.⁴³ Since chlorination of drinking water in centralized water supply systems is mandatory, many bacterial agents are excluded as potential bioagents.⁴⁴ On the other hand, biotoxins, cryptosporidium, noroviruses, and hepatitis A virus could be used as waterborne bioagents.⁴⁵ Some category C agents, such as Hantaviruses and MDR-TB, could be used for operational level.

Means and Media of Delivery

It might be assumed that terrorist groups and disaffected individuals could use drinking water and food for transmission of bioagents. Military/intelligence services might use them secretly, either by the same media of transmission or by air.

Targets

Targets and consequences could be direct or indirect. Killing people or destroying health result in political consequences. Consequences of the operational level attack could be of strategic importance. In the case of military/intelligence targets, security and stability of the state are endangered. That is why political consequences should be prompt and enormous. Attacks on “softer” targets (eg, airports, railway stations, food production industries) have direct political and indirect political (economic) consequences.

Tactical Biological Attack

A tactical biological attack is a territorially limited deployment of biological weapons on humans.

Perpetrators

Perpetrators might be military/intelligence forces (who prefer clandestine attack) or terrorist groups and individuals (who prefer publicly confirmed attacks). The perpetrators of clandestine tactical attacks have to be highly skilled, or with suicidal intent, and politically or ideologically motivated. The unknown perpetrators and lone actors dominate in this attack, as well as numerous hoaxes.

Agents

The agents from all 3 categories and emerging biological agents are potential candidates for this purpose. Biological agents are still preferred materials of hoax perpetrators at the tactical level, probably because perpetrators could easily produce and safely handle the simulated biological materials.

Means and Media of Delivery

Any kind of medium could be used. Means of delivery might be suicidal bio-bombers infiltrated in the targets, different facilities (mail), and animals (birds infected with avian influenza). Dissemination of an agent through a ventilation/air conditioning system is another powerful way of attack.

Targets

The most probable are the “hard targets,” highly prominent and protected institutions (eg, government buildings, media centers) and people (eg, politicians, scientists, high officers). “Soft targets” are ordinary people at public places (eg, respiratory agents released in crowded and closed spaces like theaters, cinemas, sports events, and political meetings). The aim of a bioattack is to produce mass effects and incite mistrust in authorities, as well as panic and fear among the population. Attacks on highly visible targets are difficult to conduct, and the biological effects are smaller than on the whole population. Even the use of biological weapons at a tactical level can cause losses with strategic dimensions. One case of SARS or avian influenza is enough to cause catastrophic economic consequences. Since Western countries have intensive food production and centralized food industries, only 1 successful bioterrorist action can contaminate a huge amount of food and threaten the lives of thousands or hundreds of thousands of inhabitants.

The importance of antibioterrorist activities in food production facilities cannot be overestimated. Such bioterrorist acts make people change their behavior for years, decades, or even permanently. For example, when food is incriminated (of suspicious quality) for a relatively short period, people can change their diet permanently. Because of fear of an attack, people may change or leave their jobs or residences, or avoid traveling to certain regions.

Bioterrorism Risk Assessment

Risk assessment (the quantification of risk) is the foundational element of risk analysis. Quantifying risk is the prerequisite for effective risk communication to policymakers and stakeholders, and for supporting critical risk management decisions by all levels of government and the private sector. Because it is not possible to fully protect every target and community against every potential threat, we need to identify the greatest risks and take the most efficient steps to reduce them.²

Using risk assessment methods, an effort is made to identify quickly and cost-effectively the first cases or exclude a bioterrorist attack possibility. The main obstacle that stands in the experts' way is insufficient existing data on which to rely.⁴⁶

Risk assessments are critical to balance preparedness against exaggeration of the threat. Early warnings could come from real-time monitoring of emergency calls, pharmacy sales, hospital or emergency admissions, or deaths, combined with the use of mathematical algorithms to detect aberrations. Examination of specific syndromes, such as febrile adults with rash, could also be useful to initiate a quicker public health response. Successful systems will be integrated into a new national electronic disease detection system that will be able to capture data from multiple sources with uniform system specifications and data standards.

Investment in our national defense at a time when we are not threatened by war ensures preparedness and acts as a deterrent against hostile acts. Similarly, investment in our public health system provides the best civil defense against bioterrorism and may also act as a deterrent. Fortunately, the tools we develop in response to bioterror threats are “dual-use” tools that will capitalize on advances in technology, information systems, and medical science.⁴⁷

Many biological agents can cause illness in humans, but not all are capable of affecting public health and medical infrastructure on a large scale. To guide national public health bioterrorism preparedness and response efforts, a method was sought for assessing potential biological threat that would provide a reviewable, reproducible means for standardized evaluations of these threats.⁴²

Examining the 2001 anthrax events in hindsight, it appears that neither the targets of attack nor the person or group responsible for attacks could have been predetermined by any known prediction methodology. When scientific knowledge about probabilities is absent, thinking about possible outcomes takes on a particular significance. One suggested partial remedy for such lack of data regarding the intent and ability of the perpetrators to perform an act of bioterrorism can therefore be vulnerability analysis. A vulnerability analysis seeks to identify a valuable asset (ie, a target) at risk of a bioterrorist attack and to conceptualize various ways in which it is vulnerable to such an attack (ie, various attack scenarios). After that, a logical consequence should be to perform a “feasibility analysis” of a biological attack.

Thus, a key aspect of policy-oriented epidemic modeling is to assess both the adequacy of current policy and how it might further be optimized. Optimalization is principally the minimization of mortality and morbidity, so it is critical that models accurately incorporate expected adverse events. However, the SARS virus has shown that the economic costs of an epidemic can be out of all proportion to the numbers infected, indicating that minimizing the duration of an outbreak might also be a critical priority when formulating control strategies.⁴⁸

A New Gradual Model of Bioterrorism Risk Assessment

A new gradual model of bioterrorism risk assessment consists of the minimum of necessary parameters for a biological attack. If we have no idea about perpetrator(s), the procedure should be as follows: the first step is to define targets that we have to protect. The second step is to define a minimum of parameters for a biological attack according to a target or a group of targets. The third step is to choose the most effective and the simplest measures to eliminate necessary parameters.

For a biological attack on predefined “hard targets,” a minimum of other necessary parameters includes perpetrator(s), agent, means/media of delivery (qualitative parameters), and accessibility to both sources of agent and target (quantitative parameters). All other parameters are contributing, but not necessary.

A biological attack on “soft targets” requires additional means/media of delivery and a significant amount of an agent. The intention of a potential attacker is difficult to predict. Therefore, limiting our vulnerability is the most promising way to prevent or mitigate biological attacks.

In reality, the most frequent scenario is the one that already has suspected perpetrator(s). It is much easier for risk assessment than the previous scenario. After introduction of further parameters, the number of possible scenarios decreases, and the accuracy of risk assessment and quality of protection increase. Within this model of biological attack, there are no sufficient components/parameters; they are all necessary or contributing components/parameters. This model allows decision makers to test assumptions and perform analyses on alternative countermeasures for reducing or eliminating credible threats, as well as to consider and compare countermeasure strategies that would be very difficult to test in a “live” environment.

Our model is transparent, user-friendly, and easily allows modeling of alternative scenarios and evaluation of various risk management strategies. In the end, only effective risk management strategies can reduce risk. We hope our model could be a useful step in bioterrorism risk assessment to understand vulnerabilities, the potential consequences of attack, and the effectiveness of mitigation strategies. The results of the assessments should directly inform risk management decision makers in reducing the risk of biological attack.

Application of Bioterrorism Risk Assessment Scoring System

In Table 2 we present a very simple scoring system within our bioterrorism risk assessment model applied on the U.S. anthrax attacks in 2001. Al-Qaeda was a main suspect the very first day of the attack. However, the application of our bioterrorism risk assessment scoring system could have pointed to an insider as the most probable perpetrator. For example, high sophistication, secrecy, individual targets, and repeated attacks might not have been expected from Al-Qaeda. The anthrax strain from the letters was modified, and this was also a low probability for terrorists as perpetrators. By concentrating intelligence efforts toward an insider instead of terrorists, it may be that the chain of attacks could have been broken earlier and some lives saved.

Table 2.

BTRA scoring of suspected perpetrators in the 2001 U.S. anthrax attacks

Parameter	Terrorist	Insider	Enemy State
Category A agent	0^a	1^b	1
Modified agent	0	1	1
Postal delivery	1	1	0
Letters sent from U.S.	1	1	0
Both soft and hard targets	0	1	0
High sophistication	0	1	1
High ability	1	1	1
High secrecy	0	1	1
Individual targets	0	1	0
Repeated attack	0	1	0
Total score	3	10	5

Low probability.

Highly probable.

Conclusions

This is an attempt to systematically classify components, parameters, and types of a bioterrorist attack and to introduce a simple model of bioterrorism risk assessment scoring. By raising the number of scored parameters, the odds of narrowing the rim around a perpetrator increase. We think this model could shorten the time for breaking bioterrorist attacks. It may be helpful both in analyzing previous bioterrorist attacks and in building high-probability scenarios of bioterrorist attacks, within the preparation of public health services for bioterrorist attacks. In our opinion, this is a quickly applicable framework, particularly for health and security professionals and policymakers who are less familiar with risk assessment. The whole community could benefit from this framework through better organization and protection in the case of a bioterrorist attack. This model is the first step in this effort.

Footnotes

Acknowledgments

This study was financially supported by the Serbian Ministry of Science, Contract No. 145013, 2006-2010.

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