Statement of Task
To address the issue of appropriate cleanup levels for decontamination of public transportation facilities (e.g., airports, subways) affected by exposure to harmful biological agents, the National Academies will convene an ad hoc committee of experts to conduct a study that will be designed to lay the technical foundations for the establishment of standards and policies for biological decontamination. Elements of the study will include:
Infectious dose: Because differences among organism types may require fundamentally different approaches for decontamination and risk assessment, the committee will evaluate the current understanding of infectious dose for key biowarfare-related biologicals (e.g., Bacillus anthracis). This will include relevant representative organisms among the infectious/noncontagious and infectious/contagious gram-positive and gram-negative bacteria and viral pathogen classes. Given that some biological agents degrade rapidly without treatment so that decontamination is not necessary, the committee will first identify members of each key group that require decontamination, and then select one or two representatives of each key group for in-depth assessment. In addition to lethal pathogens, the committee may also consider pathogens that may typically be nonlethal, but whose virulence may result in the incapacitation of large numbers of people, thereby causing disruption and panic. The 2001 anthrax attacks called the state of knowledge on infectious dose for this organism into serious question. The committee will assess the validity and uncertainty associated with current knowledge of infectious doses and identify areas in which additional knowledge from research is required. The committee will first examine the existing dose–response models for each selected organism. It will then evaluate whether there is a threshold dose below which there is no impact (infectious dose zero, ID0). An
important part of this study is to understand existing natural environmental background levels for various microorganisms and their potential effect on the surrounding population. Individuals tolerate certain levels of microbial pathogens in the environment and these levels need to be taken into account in assessing risk. The committee will also determine the cleanup levels associated with a range of infectious doses (e.g., 1:1,000,000 to 1:10,000, or ID10−6 to ID10−4) and describe how these data could be used to assist in establishing acceptable measures of decontamination for selected organisms.
Quantitative risk assessment models: The committee will examine existing quantitative risk assessment models and evaluate whether these models can be adapted for purposes of assessing the safety of decontaminated public transportation facilities or whether new models need to be developed. In either case, the committee will develop the conceptual components of the four risk assessment steps (hazard identification, exposure assessment, dose–response assessment, and risk characterization) for the key organism types considered in the study. Hazard identification identifies aspects of the organisms (e.g., infectivity) and situations (e.g., form of biological hazard, such as fine aerosol) that represent threats to human health. Exposure assessment estimates the dose encountered considering the sources (including existing environmental background levels), spatial distribution of organisms, duration of exposure, and exposure pathways (ingestion, inhalation, and dermal exposure). Dose–response assessment uses available data to relate dose to adverse health response. Risk characterization combines exposure and dose–response assessment to quantify, for a defined population (considering, for example, age, sex, ethnicity, and overall health of population) the risks predicted to result from the exposure. The committee will test the models for relevant representative organisms to assess the potential risk associated with identified options for clean up levels.
Natural and residual contamination: An additional component for the committee to consider is the means of estimating the exposure level that could arise from residual contamination at various locations in a facility (e.g., inside air ducts or from equipment). The committee will comment on the role of the time factor for degradation in various environments (with and without treatment) to help determine decontamination approaches and requirements. The committee will evaluate various approaches (for example, monitoring schemes and performance evaluation targets) and describe how this information could be used to assist in determining safe levels of residual contamination. Relevant information on natural environmental backgrounds that individuals encounter with few or no health effects will also be included and evaluated here.
Past cleanup efforts: The committee will review the various efforts put into the cleanup of B. anthracis following the events of last year in order to more completely understand the implications of exposure and dose to infectivity and immunity. These reviews will look at both federal and private efforts, including the ongoing cleanup in Florida.