June 6, 2003
Good morning, Mr. Chairman and Members of the Committee. I am Dr. Ali Khan, Associate Director for Medical Science, Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC). I am accompanied today by Mr. Joseph M. Henderson, CDC's Associate Director of Terrorism Preparedness and Emergency Response. Thank you for the invitation to participate today in this hearing on the challenges and progress made in identifying agents that could be used as biological weapons. I will outline the overall selection and prioritization process used to determine the biological agents for CDC's public health preparedness activities.
As part of a Congressional initiative begun in 1999 to upgrade national public health capabilities for response to acts of biological terrorism, CDC was designated the lead agency for overall public health planning. An Office of Terrorism Preparedness and Emergency Response has been formed to help provide strategic direction across CDC, targeting areas to enhance preparedness activities, planning, improved surveillance and epidemiologic capabilities, rapid laboratory diagnostics, communications, and the delivery of medical therapeutics stockpiling. To focus these preparedness efforts, however, the biological agents toward which the efforts should be targeted had to be first formally identified and prioritized according to the level of threat posed. These agents make up CDC's critical agent list. This list is used as the framework for guidance to the state and local preparedness programs, determining the formulary for the Strategic National Stockpile, developing public health response plans and determining reagents and protocols for the Laboratory Response Network (LRN). The presence of anthrax on this list led to the focused preparedness efforts on drug stockpiles and diagnostic tests that were available during the 2001 anthrax attack.
A number of similar lists do exist such as the military's formal assessment of multiple agents for their strategic usefulness on the battlefield; an international list of agents for export control; a list of agents that have been processed for biowarfare; and classified lists. Most of these lists focused on biowarfare, but for public health preparedness purposes, CDC needed a list of agents that could have significant impact on the U.S. population. To guide the national public and medical health bioterrorism preparedness and response efforts, we devised a method for assessing potential biological threat agents that would provide a reviewable, reproducible means for standardized evaluations of these threats. Identifying these priority agents helps facilitate coordinated planning efforts among federal agencies, state and local emergency response and public health agencies, and the medical community.
Overview of Agent Selection and Prioritization Process
In June 1999, CDC convened a meeting of academic infectious disease experts, national public health experts, Department of Health and Human Services agency representatives, civilian and military intelligence experts, and law enforcement officials to review and comment on the threat potential of various agents to civilian populations. While biological agents can cause illness in humans, not all are capable of affecting public health and medical infrastructures on a large scale. The following four general criteria were used to assess this public health impact: 1) the anticipated amount of illness and death with an agent; 2) the delivery potential to large populations based on stability of the agent, ability to mass produce and distribute a virulent agent, and potential for person-to-person transmission; 3) the public perception as related to fear and potential civil disruption; and 4) the special public health preparedness needs based on stockpile requirements, enhanced surveillance, or diagnostic tools necessary to respond to a deliberate dissemination of an agent. These last two criteria were the unique features of the public health critical agent list.
Participants discussed and identified these four criteria and reviewed available lists to subjectively place agents they felt had the potential for high impact. Participants with appropriate clearance levels also reviewed intelligence information regarding classified suspected biological agent threats to civilian populations. Genetically engineered or recombinant biological agents were considered but not included for final prioritization because of the inability to predict the nature of these agents and thus identify specific preparedness activities for public health and medical response to them. In addition, no information was available about the likelihood for use of one biological agent over another. This aspect, therefore, could not be considered in the final evaluation of the potential biological threat agents.
After the meeting, CDC personnel then attempted to identify objective indicators in each category that could be used to further define and prioritize the identified high impact agents and provide a framework for an objective risk-matrix analysis process for any potential agent. The agents were evaluated in each of the general areas according to the objective parameters. Final category assignments (A, B, or C) of agents for public health preparedness efforts were then based on an overall evaluation of the ratings the agents received in each of the four areas.
Categories of Agents
Based on the overall criteria and weighting, agents were placed in one of three priority categories for initial public health preparedness efforts: A, B, or C. Agents in Category A have the greatest potential for adverse public health impact with mass casualties, and most require broad-based public health preparedness efforts (e.g., improved surveillance and laboratory diagnosis and stockpiling of specific medications). Category A agents also have a moderate to high potential for large-scale dissemination or a heightened general public awareness that could cause mass public fear and civil disruption.
Most Category B agents also have some potential for large-scale dissemination with resultant illness, but generally cause less illness and death and therefore would be expected to have lower medical and public health impact. These agents also have lower general public awareness than Category A agents and require fewer special public health preparedness efforts. Agents in this category require some improvement in public health and medical awareness, surveillance, or laboratory diagnostic capabilities, but presented limited additional requirements for stockpiled therapeutics beyond those identified for Category A agents. Biological agents that have undergone some development for widespread dissemination but do not otherwise meet the criteria for Category A, as well as several biological agents of concern for food and water safety, are included in this category.
Biological agents that are currently not believed to present a high bioterrorism risk to public health but which could emerge as future threats (as scientific understanding of these agents improves) were placed in Category C. These agents will be addressed nonspecifically through overall bioterrorism preparedness efforts to improve the detection of unexplained illnesses and ongoing public health infrastructure development for detecting and addressing emerging infectious diseases.
Agents were categorized based on the overall evaluation of the different areas considered. For example, smallpox would rank higher than brucellosis in the public health impact criterion because of its higher untreated mortality (approximately 30% for smallpox and less than or equal to 2% for brucellosis); smallpox has a higher dissemination potential because of its capability for person-to-person transmission. Smallpox also ranks higher for special public health preparedness needs, as additional vaccine must be manufactured and enhanced surveillance, educational, and diagnostic efforts must be undertaken. Inhalational anthrax and plague also have higher public health impact ratings than brucellosis because of their higher morbidity and mortality. Although mass production of Vibrio cholerae (which causes cholera) and Shigella species (which cause shigellosis) would be easier than the mass production of anthrax spores, the public health impact of widespread dissemination would be less because of the lower morbidity and mortality associated with these agents and because of some of the preparedness efforts implemented for other agents such as drug stockpiles.
The above categories of agents should not be considered definitive. Agents in each category may change as new information is obtained or new assessment methods are established. To date, changes to these lists have not been warranted. Disease elimination and eradication efforts may result in new agents being added to the list as populations lose their natural or vaccine-induced immunity to these agents. Conversely, the priority status of certain agents may be reduced as the identified public health and medical deficiencies related to these agents are addressed (e.g., once adequate stores of smallpox vaccine and improved diagnostic capabilities are established, its overall rating within the risk-matrix evaluation process might be reduced). To meet the ever-changing response and preparedness challenges presented by bioterrorism, a standardized and reproducible evaluation process similar to the one outlined above will continue to be used to evaluate and prioritize currently identified biological critical agents, as well as new agents that may emerge as threats to civilian populations or national security.
In conclusion, CDC is committed to working with other Federal agencies, academia, and other partners, as well as State and local public health departments, to ensure the health and medical care of our citizens. We have made substantial progress to date in enhancing the Nation's capability to prepare for and respond to a bioterrorist event. The best public health strategy to protect the health of civilians against a biological attack is the development, organization, and enhancement of public health prevention systems and tools. Priorities include strengthened public health laboratory capacity; increased surveillance and outbreak investigation capacity; and health communications, education, and training at the Federal, State, and local levels. Not only will this approach ensure that we are prepared for deliberate bioterrorist threats, but it will also ensure that we will be able to recognize and control naturally occurring new or re-emerging infectious diseases such as SARS or pandemic influenza. A strong and flexible public health infrastructure is the best defense against any disease outbreak.
Thank you very much for your attention. I will be happy to answer any questions you may have.
Last Revised: June 10, 2003