2001 ATTACKS AND CLEANUP
Although the anthrax attacks of 2001 did not cause catastrophic morbidity or mortality—5 people died and more than 20 were infected—those incidents resulted in considerable disruption. They had enormous economic and social consequences for the nation. The “anthrax letters” contaminated postal facilities, offices, and residences that required extensive and expensive decontamination. In addition to the economic cost, the attacks caused anxiety and contributed to a nationwide sense of vulnerability: According to one national poll (Blendon et al., 2001), in late November 2001, a third of the U.S. population took precautions in handling mail.
Several groups have noted the dearth of information to guide decontamination efforts. In the wake of the 2001 attacks, the National Academies undertook an effort to define a roadmap for actions that resulted in Making the Nation Safer: The Role of Science and Technology in Countering Terrorism (2002). Summarizing information on the state of the art for rendering facilities and the larger environment safe after a biological attack, that report concluded that more information is needed about dose–response relationships, cleanup criteria, and effective decontamination (Box 1-1).
Before the anthrax attacks, the Working Group on Civilian Biodefense had made several recommendations for medical and public health management after exposure to the highest priority biological weapons (Arnon et al., 2001; Borio et al., 2002; Dennis et al., 2001; Henderson et al., 1999; Inglesby et al., 1999, 2000). The working group is an expert panel convened by the former Center for Civilian Biodefense Strategies at the Bloomberg School of Public Health at Johns Hopkins
Making the Nation Safer (2002) illustrates that much of the information required to quantify the cleanup required to safeguard public health needs in the event of a bioterrorist attack is lacking. Research should be done to fill the knowledge gaps and develop decontamination protocols (pp. 94–95):
At present there are few data on which to base decontamination procedures, particularly for biological agents. A review of the literature shows that dose–response information is often lacking or controversial, and that regulatory limits or other industrial health guidelines (which could be used to help establish the maximum concentrations of such agents for declaring a “decontaminated” environment) are generally unavailable or not applicable to public settings (Raber et al., 2001). Moreover, the correct means for identifying the presence of many biological agents are not known, nor is the significance of the presence of biological agents in the natural environment (e.g., anthrax spores are found in the soil in some parts of the United States). Research is therefore needed to determine what level of cleanup will be required to meet public health needs in the aftermath of a bioterrorist attack.
Although the lack of dose information, cleanup criteria, and decontamination protocols presents challenges to effective planning, several decontamination approaches are available. Such approaches should be combined with risk-informed decision making to establish reasonable cleanup goals for the protection of health, property, and resources. Efforts in risk assessment should determine what constitutes a safety hazard and whether decontamination is necessary. Modeling exercises are needed that take into consideration the characteristics of a particular pathogen, public perceptions of the risk that the pathogen poses to their health, the level of public acceptance of recommendations based on scientific criteria, levels of political support, time constraints in responding to the threat posed by a pathogen, and economic concerns (Raber et al., 2001).
University in Baltimore, Maryland. That group issued consensus statements on medical and public health guidelines for diagnosing, treating, and managing health effects that could result from future bioterrorist attacks. The position papers addressed some aspects of decontamination, but they did not consider the amount of cleanup necessary to meet the needs of interested and affected parties. In the absence of technically sound guidance, it is difficult to define what constitutes an adequate extent of cleanup from a public health perspective. Recent experience has shown that extensive and repeated cleanup, in the context of uncertain risk, could incur substantial costs without additional benefit.
Even though thousands of people have reentered the buildings that were decontaminated, 3 years after the attacks we still face the same fundamental
question: “How clean is safe?” If we experience another bioterrorist attack, we should be prepared to ensure the safety of facilities in a more timely manner.
CONTEXT OF THE STUDY AND CHARGE TO THE COMMITTEE
This study was sponsored by the Department of Homeland Security as part of a larger project, run by the Lawrence Livermore and Sandia National Laboratories, called the Restoration and Domestic Demonstration and Application Program. That program focuses on developing procedures, plans, and technologies for the rapid, safe restoration of transportation nodes after a biological attack. The primary focus of the demonstration project is major airports, which were chosen for the scenario because an attack at an airport, in addition to the likely health effects, would cause major transportation disruption and would have serious economic consequences. Effective and efficient decontamination and restoration of such a facility would be imperative to minimize social and economic harm.
At the initial meeting, the Committee on Standards and Policies for Decontaminating Public Facilities Affected by Exposure to Harmful Biological Agents heard from representatives of Lawrence Livermore National Laboratory. Representatives from the sponsoring agency explained that additional information was needed for the demonstration project. Because of the specific request from the sponsor, this study is not a review of all issues that would need to be considered in the aftermath of a biological attack. Rather, it examines relevant issues and the steps that would lead to a decision to reoccupy a decontaminated building. For clarity, some of the issues that are the focus of the study are listed here:
The study focuses on large buildings, such as airports, and does not consider outdoor contamination. (Two wide-area restoration projects are under way by other groups, the Homeland Security Institute and Clean Earth Technologies.)
The committee was asked to examine the final stages of cleanup. Therefore, the report does not address in any detail the risk that such an attack would occur, emergency response to an attack, decisions about whether to initiate cleanup or raze a facility, issues related to the appropriate allocation of resources for research or response, or broader public health issues related to transmissible diseases. The report does not recommend decontamination methods for given circumstances, although some techniques are discussed to provide information to those who would make final cleanup decisions.
The committee was charged with laying the technical foundations for establishing standards and policies. Where the committee determined that social science considerations would be important in formulating such standards and policies, those issues are addressed. However, the committee was not specifically assigned topics such as education of participants in the decision-making process or communicating with the public about risk; those topics are not covered in detail here.
The committee was specifically asked to consider a scenario in which decontamination of a facility approaches completion. It was directed to assess the criteria that must be met for a cleanup to be declared successful, thus allowing the reoccupation. This committee has therefore reviewed the factors that influence decision making and that lay the foundation for establishing standards and policies for relevant aspects of biological decontamination. It was asked to examine four specific topics: infectious dose, quantitative risk assessment, natural and residual contamination, and past cleanup efforts (see Appendix A for the complete Statement of Task). In responding, the committee considered the tasks and reorganized them into the five groups described here.
The 2001 anthrax attacks called into question the state of knowledge on infectious dose for Bacillus anthracis. The term infectious dose often has been used to denote the number of organisms that are believed necessary to overwhelm the host defense mechanism and establish an infection that can lead to disease. The committee was asked to evaluate the current understanding of infectious dose for warfare-related biological agents such as B. anthracis and to assess the validity and uncertainty associated with knowledge of infectious doses. The report was to discuss relevant representative organisms among the infectious–nontransmissible and infectious–transmissible gram positive and gram negative bacteria and viral pathogen classes to identify areas in which additional research is required.
The committee was asked to examine what is known about natural environmental background concentrations of various microorganisms and their potential effects on surrounding populations. People tolerate some exposure to microbial pathogens in the environment and those concentrations must be considered in assessing risk. Relevant information on natural environmental background contamination that causes few or no human health effects was to be evaluated.
Quantitative Risk Assessment
The committee was asked to examine quantitative risk assessment models (Box 1-2 lists various definitions) and evaluates their suitability for application to the safety of decontaminated public transportation facilities. The committee was asked to develop the conceptual components of the four risk assessment steps (hazard identification, exposure assessment, dose–response assessment, and risk characterization) for the organism types considered in the study.
Hazard identification identifies aspects of the organisms (such as infectivity) and situations (form of biological hazard, for example, fine aerosol) that represent threats to human health.
Exposure assessment estimates the dose encountered, considering sources (including environmental background), spatial distribution, duration of exposure, and pathway (ingestion, inhalation, dermal).
Dose–response assessment uses available data to relate dose to adverse health response. The committee examined the existing dose–response models for each selected organism and attempted to determine whether there is a threshold dose below which there is no effect (infectious dose zero, ID0).
Risk characterization combines exposure and dose–response assessment to quantify, for a defined population (considering age, sex, ethnicity, and overall health), the risks predicted to result from the exposure. The committee was asked to test the models for relevant representative organisms to assess the potential risk associated with identified options for specific amounts of cleanup. The committee was to determine the cleanup associated with a range of infectious doses—1:1,000,000 or ID 10-6 to 1:10,000 or ID 10-4. An infectious dose of 1:1,000,000, also known as ID 10-6, describes the dose that would result in 1 infection in 1 million people. It was to describe how those data could be used in establishing acceptable measures of decontamination for selected organisms.
Past Cleanup Efforts
The committee was asked to review the efforts to clean up B. anthracis in 2001 to more completely identify the implications of exposure and dose for infectivity and immunity. The review was to examine federal and private efforts, including the cleanup of the American Media, Inc., building in Boca Raton, Florida.
The committee was asked to address whether some biological agents degrade rapidly enough that decontamination is not necessary. Part of that charge was an in-depth assessment of representative organisms that would require decontamination and a discussion of the time factor for degradation in various environments (with and without treatment) to help determine decontamination approaches and requirements. An additional component for the committee to consider was the means of estimating the exposure that could arise from residual contamination at various locations in a facility (inside air ducts or on equipment). The committee was asked to evaluate various approaches, including monitoring methods and performance evaluation targets, and describe how the information could be used to assist in determining safe concentrations of residual contamina-
“Risk Assessment is the process of establishing information regarding acceptable levels of a risk and/or levels of risk for an individual, group, society, or the environment.” (Risk Assessment Information Glossary, U.S. Department of Energy, Office of Environmental Management, Oak Ridge Operations Office. Online: http://risk.lsd.ornl.gov/homepage/glossary.shtml#R)
“An ecological risk assessment evaluates the potential adverse effects that human activities have on the plants and animals that make up ecosystems. The risk assessment process provides a way to develop, organize and present scientific information so that it is relevant to environmental decisions. When conducted for a particular place such as a watershed, the ecological risk assessment process can be used to identify vulnerable and valued resources, prioritize data collection activity, and link human activities with their potential effects. Risk assessments can also provide a focal point for cooperation among local communities and state and federal government agencies. Risk assessment results provide a basis for comparing different management options, enabling decision makers and the public to make better informed decisions about the management of ecological resources.” (EPA National Center for Environmental Assessment. Online: http://cfpub.epa.gov/ncea/cfm/ecologic.cfm)
“The process of establishing information regarding acceptable levels of a risk and/or levels of risk for an individual, group, society, or the environment.” (Glossary from the Society for Risk Analysis. Online: http://www.sra.org/resources_glossary_p-r.php)
“Risk assessment is essential for setting occupational safety and health priorities and for demonstrating health impairment when promulgating occupational standards. Risk assessment has been most often applied in assessing the risk of carcinogens, often with animal bioassay data. However, evaluation of these procedures has been limited, and questions abound as to whether the resulting risk estimates are reasonable. Risk assessment for noncarcinogens, particularly quantitative approaches, is even less well developed. Improved methods are needed for using animal bioassay data and human health effects data to generate risk estimates for cancer and noncancer effects and injury.” (National Occupational Research Agenda of CDC. Online: http://www.cdc.gov/niosh/nrram.html)
“Risk assessment is a process in which hazard, exposure, and dose–response information are evaluated. These evaluations determine whether an exposed population is at greater-than-expected risk of disease (cancer or noncancer endpoints) or injury. Once this is established, the magnitude and nature of the increased risk can be explored further, using either qualitative or quantitative approaches. Qualitative risk assessments are generally descriptive and indicate that disease or injury is likely or unlikely under specified conditions of exposure. On the other hand, quantitative risk assessments provide a numerical estimation of risk based on mathematical modeling. For example, under given specific exposure conditions, it is expected that one person per 1,000 would develop a disease or injury.
Quantitative risk assessments require (1) data providing as much detail as possible on exposures relevant to the adverse health outcomes of interest, and (2) development of a mathematical model describing that exposure–response relationship. Risk assessments based on experimental animal and molecular biologic data provide detailed information on the exposure–response relationships. However, there is often substantial concern about the validity of using risk assessments based on susceptible animal species tested at high constant doses to estimate the risks to workers who may have much lower and more variable workplace exposures. Risk assessments based on epidemiologic, population-based studies may have real-world relevance to workers, but they generally suffer from a number of limitations. These include potential confounding by risk factors for exposures other than the exposure of interest, variability in workplace exposures for any particular substance or mixture of exposures, individual variability in health response, and detection of statistically significant changes in adverse health outcomes. The integration of mechanistic data, human data, toxicity testing data, and biomathematics can be useful for developing methods that strengthen the scientific foundation on which risk assessments are based.
The risk assessment process has become increasingly formal and sophisticated over the past decade. There are many who support a greatly expanded and even more formal role for risk assessment in establishing national priorities and providing a justification for regulatory actions by Federal agencies. In occupational safety and health regulation, that process began when the U.S. Supreme Court ruled in the ‘benzene decision’ [Industrial Union Department v. American Petroleum Institute, 448 U.S. 607 (1980)] that the Occupational Safety and Health Administration (OSHA) could not issue a standard without demonstrating a significant risk of material health impairment. The ruling allowed (but did not demand) that numerical criteria could be used to determine whether a risk is ‘significant.’ As a result of that Supreme Court ruling, risk assessment became standard practice in OSHA rulemaking for health standards, and quantitative risk assessments are preferred whenever data, modeling techniques, and biological understanding are adequate to support their development.
“Research to improve risk assessment methods is needed from a wide range of scientific disciplines to provide more reliable methods for estimating the risk of adverse effects related to work. Substantial controversy surrounds currently available cancer risk assessment models, and models for noncancer effects are even less well developed. Lagging even more are methods for assessment of safety risks. Innovative and practical new approaches to modeling are needed. In addition, research needs to be directed to the following areas: designing epidemiologic and toxicologic studies that provide detailed and accurate exposure–response relationship data for specific hazards; generating more data on which to base models that include intake distribution, metabolism, and elimination; developing biologic markers for exposures and effects; and utilizing existing occupational safety and health data to ensure that human observations complement and validate risk estimates derived from animal data. Research efforts should also evaluate how risk assessment estimates are used in risk management, communicated to the public, and perceived by workers and employers.” (National Institute for Occupational Safety and Health, National Occupational Research Agenda, Risk Assessment Methods, Additional Information. Online: http://www2a.cdc.gov/nora/NaddinfoRisk.html)
tion. The committee was given the option of considering pathogens that typically are nonlethal, but whose virulence can result in the incapacitation of large numbers of people, thereby causing disruption, fear, and anxiety.
CONTENT AND STRUCTURE
In the context of an incomplete scientific record, controversy has arisen over the response to the anthrax letter attacks and the extent to which the United States is prepared for the possibility of future terrorist attacks. This report provides a decision-making framework with which to approach the safe return of the public to a building that has been decontaminated after a biological attack.
The report consists of three parts. Part I provides background information. This chapter describes the purpose and gives an overview of the report. Chapter 2 discusses the complex nature of the relationship between humans and microorganisms and the use of microorganisms as biological weapons. It also reviews microbiological, clinical, and epidemiological features of the agents of greatest concern to national security and public health policy. Chapter 3 reviews U.S. history and policy related to the remediation of microbiological, chemical, and radiological contamination. Although the case studies described in Chapter 3 are not directly related to terrorist attacks, many of the lessons learned in managing contamination are relevant. Chapter 4 chronicles the public health consequences of the release of a weaponized1 form of anthrax in the fall of 2001 and the social, political, and practical challenges posed by cleanup efforts.
Part II surveys risk-based approaches for cleanup after an attack and describes the challenges of using those approaches and the technical protocols that could be applied. Part II contains information that is pertinent to decision making on safe reoccupation. It is organized into five separate chapters to aid readers who seek specific technical information. Chapter 5 evaluates the applicability of a risk assessment and management framework. Chapters 6, 7, and 8 consider in significant detail current limitations to identifying microbial contaminants, modeling population exposure, and analyzing dose–response relationships. Chapters 9 and 10 review sampling technologies and strategies and describe practices and principles for decontamination based on current knowledge and experience.
Drawing from the biological information and the social context of Part I and the technical context of Part II, Chapter 11 sketches a generic framework for making decisions about safe return to a building affected by a biological attack. Chapter 12 describes an ideal, proactive strategy for quickly and safely returning an airport and other public buildings to use.
Because of the relative lack of data on other potential biological weapons, the report primarily uses weaponized B. anthracis as its example. No claim is made that experiences are directly transferable to other pathogens, but in many cases they provide the best information available on the issues that must be considered for making decisions about decontamination.
The 2001 anthrax attacks and cleanups brought into sharp relief the knowledge that the United States lacked the necessary information to make scientifically sound, socially acceptable decisions about when buildings might be safely reoccupied after a harmful biological exposure. Although all the scientific and technical information related to harmful biological agents—for exposure, decontamination, and subsequent reoccupation—might not be available, building managers and decision makers are still responsible for decontaminating an affected facility and ensuring the safety of its occupants. Decontamination policies and practices can be developed now despite the knowledge gaps, and such policies and guidelines can be improved using an iterative process that builds on new research findings.
The committee was asked to assess risk for various amounts of residual contamination. It concludes that current data are insufficient to determine correlations. More research on dose–response relationships would allow scientists to narrow the uncertainty associated with the risks. However, even with improved correlations, the decision to reopen a facility is a complex issue that involves social decisions about what constitutes “safe.” This report provides a framework for thinking about issues that must be considered in the decision to reopen a facility after an attack. The committee hopes that it serves as a resource to help decision makers better understand the relevant concerns.
In addressing its charge, the committee reached specific conclusions for each of the areas described above: infectious dose, natural background, risk assessment, past cleanup efforts, and residual contamination.
The 2001 anthrax attacks called into question the state of knowledge on infectious dose for B. anthracis. The committee concluded that infectious doses for harmful biological agents that can be used as weapons cannot be determined with confidence because the infectivity and virulence of harmful agents can vary by strain, within species, and by type of preparation for weapons. Currently available data on dose–response relationships are not as detailed as demanded by modern scientific standards, in most cases covering only exposure in young healthy adults.
The committee acknowledges that natural environmental background concentrations of various microorganisms have been assessed in some places and that most people tolerate exposure without adverse effects. One hypothesis is that those people might have developed immunity through exposure. The concept of natural background might not apply to acts of bioterrorism in indoor public facilities because it is unlikely that a detectable natural background concentration of weaponized agents, such as those in the Centers for Disease Control and Prevention’s (CDC’s) highest risk group, Category A,2 are present in indoor public facilities. Moreover, the agent used in an act of bioterrorism could deviate from its natural form, depending on whether the weaponization process alters its characteristics.
Quantitative Risk Assessment
Quantitative risk assessment models often are used to evaluate complex situations. The models traditionally have four steps—hazard identification, exposure assessment, dose–response assessment, and risk characterization. Various definitions of risk assessment are presented in Box 1-2. A complete risk assessment of the most thorough type described there would exceed the charge to this committee. However, aspects of such models could be useful for assessing risks of exposure to harmful biological agents after cleanup, even though the essential data to support thorough analysis by quantitative risk assessment are currently lacking for some agents that might be used as biological weapons. An example of how such data would be used to evaluate risk in the very last stages of a cleanup is presented in Chapter 8 and Appendix E.
Projects in the area of risk assessment for biological hazards, such as those of the U.S. Army Center for Health Promotion and Disease Prevention, and the Department of Homeland Security’s Biological Threat Information Center, which is part of the National Biodefense Analysis and Countermeasures Center, should be noted. They could provide information for use in the future to allow for more precise calculations of risk.
Past Cleanup Efforts
The cleanup of B. anthracis following the events of 2001 provides insights about the approaches that should be used in the event of a future attack.
The CDC’s categories are discussed in Chapter 2.
Some biological agents in their natural forms would likely degrade rapidly enough that extensive cleanup would not be necessary after an initial decontamination. However, a preliminary analysis of the agent used as a weapon might not reveal alterations that could affect its viability. Therefore, a full characterization of the agent would be necessary to evaluate the effect of genetic or physical modifications on its viability before an informed decision could be made about cleanup. After cleanup, continuous medical monitoring might be useful to ensure the safety of those who would use the decontaminated space.
The committee concluded that there is insufficient information on which to base “safe” numbers of residual biological agents for a decontaminated facility. Further research could provide additional information on infectious dose that would decrease the uncertainties and make a quantitative approach more useful. However, the risk different people or groups of people are willing to tolerate will always vary. Therefore, the issues related to decision making raised in this report will continue to be relevant. The report considers lessons from the response to the 2001 anthrax attacks and from other situations involving chemical or radiological decontamination; the idea of a risk assessment framework, including current knowledge of dose–response relationships; the role of indoor air movement; the various approaches to sampling for biological agents; and the technologies available for decontamination. All of those issues would be important for decision makers to consider in the event a facility requires decontamination.
Based on its analysis of the issue areas listed above, the committee made 26 recommendations.
Arnon, S.S., R. Schechter, T.V. Inglesby, D.A. Henderson, J.G. Bartlett, M.S. Ascher, E.M. Eitzen, Jr., A.D. Fine, J. Hauer, M. Layton, S. Lillibridge, M.T. Osterholm, T. O’Toole, G. Parker, T.M. Perl, P.K. Russell, D.L. Swerdlow, and K. Tonat. 2001. Botulinum toxin as a biological weapon: medical and public health management. Journal of the American Medical Association 285(8): 1059-1070.
Blendon, R.J., J.M. Benson, C.M. DesRoches, and M.J. Herrmann. 2001. Harvard School of Public Health/Robert Wood Johnson Foundation survey project on Americans’ response to biological terrorism, study 2: National and three metropolitan areas affected by anthrax, November 29-December 3, 2001. [Online]. Available at: http://www.hsph.harvard.edu/press/releases/blendon/report2.pdf (accessed 7 January, 2002).
Borio, L., T.V. Inglesby, C.J. Peters, A.L. Schmaljohn, J.M. Hughes, P.B. Jahrling, T. Ksiazek, K.M. Johnson, A. Meyerhoff, T. O’Toole, M.S. Ascher, J. Bartlett, J.G. Breman, E.M. Eitzen, Jr., M. Hamburg, J. Hauer, D.A. Henderson, R.T. Johnson, G. Kwik, M. Layton, S. Lillibridge, G.J. Nabel, M.T. Osterholm, T.M. Perl, P. Russell, and K. Tonat. 2002. Hemorrhagic fever viruses as biological weapons: medical and public health management. Journal of the American Medical Association 287(18): 2391-2405.
Dennis, D.T., T.V. Inglesby, D.A. Henderson, J.G. Bartlett, M.S. Ascher, E.M. Eitzen, Jr., A.D. Fine, A.M. Friedlander, J. Hauer, M. Layton, S.R. Lillibridge, J.E. McDade, M.T. Osterholm, T. O’Toole, G. Parker, T.M. Perl, P.K. Russell, and K. Tonat. 2001. Tularemia as a biological weapon: medical and public health management. Journal of the American Medical Association 285(21): 2763-2773.
Henderson, D.A., T.V. Inglesby, J.G. Bartlett, M.S. Ascher, E. Eitzen, P.B. Jahrling, J. Hauer, M. Layton, J. McDade, M.T. Osterholm, T. O’Toole, O. Parker, T. Perl, P.K. Russell, and K. Tonat. 1999. Smallpox as a biological weapon: medical and public health management. Journal of the American Medical Association 281: 2127-2137.
Inglesby, T.V., D.A. Henderson, J.G. Bartlett, M.S. Ascher, E. Eitzen, A.M. Friedlander, J. Hauer, J. McDade, M.T. Osterholm, T. O’Toole, G. Parker, T.M. Perl, P.K. Russell, and K. Tonat. 1999. Anthrax as a biological weapon: medical and public health management. Journal of American Medical Association 281:1735-1963.
Inglesby, T.V., D.T. Dennis, D.A. Henderson, J.G. Bartlett, M.S. Ascher, E. Eitzen, A.D. Fine, A.M. Friedlander, J. Hauer, J.F. Koerner, M. Layton, J. McDade, M.T. Osterholm, T. O’Toole, G. Parker, T.M. Perl, P.K. Russell, M. Schoch-Spana, and K. Tonat. 2000. Plague as a biological weapon. Medical and public health management. Journal of American Medical Association 283: 2281-2290.
NRC (National Research Council). 2002. Making the Nation Safer: The Role of Science and Technology in Countering Terrorism. Washington, DC: National Academy Press.
Raber, E., A. Jin, K. Noonan, R. McGuire, and R.D. Kirvel. 2001. Decontamination issues for chemical and biological warfare agents: how clean is clean enough? International Journal of Environmental Health Research 11: 128-148.