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Responding to Detection of Aerosolized Bacillus anthracis by Autonomous Detection Systems in the Workplace
Patrick J. Meehan, M.D.;1
The material in this report originated in the National Center for Environmental Health/Agency for Toxic Substances and Disease Registry, Office of the Director, Henry Falk, M.D., Director; National Center for Infectious Diseases, James M. Hughes, M.D.; the Division of Bacterial and Mycotic Diseases, Mitchell L. Cohen, M.D., Director; and the Bioterrorism Preparedness and Response Program, Charles A. Schable, M.D., Director; National Institute for Occupational Safety and Health, Office of the Director, John Howard, M.D., Director; and Office for Terrorism Preparedness and Emergency Response, Office of the Director, Joseph M. Henderson, M.P.A., Director.
Autonomous detection systems (ADSs) are under development to detect agents of biologic and chemical terror in the environment. These systems will eventually be able to detect biologic and chemical hazards reliably and provide approximate real-time alerts that an agent is present. One type of ADS that tests specifically for Bacillus anthracis is being deployed in hundreds of postal distribution centers across the United States. Identification of aerosolized B. anthracis spores in an air sample can facilitate prompt on-site decontamination of workers and subsequent administration of postexposure prophylaxis to prevent inhalational anthrax.
Every employer who deploys an ADS should develop detailed plans for responding to a positive signal. Responding to ADS detection of B. anthracis involves coordinating responses with community partners and should include drills and exercises with these partners. This report provides guidelines in the following six areas: 1) response and consequence management planning, including the minimum components of a facility response plan; 2) immediate response and evacuation; 3) decontamination of potentially exposed workers to remove spores from clothing and skin and prevent introduction of B. anthracis into the worker's home and conveyances; 4) laboratory confirmation of an ADS signal; 5) steps for evaluating potentially contaminated environments; and 6) postexposure prophylaxis and follow-up.
The risk for terrorist events involving the intentional airborne release of infectious agents has led to development of new approaches for sampling and testing ambient air both indoors and outdoors (1). One such approach is the use of an autonomous detection system (ADS) that combines automated air sampling and testing. An ADS continuously samples air that impinges in a buffer solution. An automated detection assay (e.g., a real-time polymerase chain reaction [PCR] test or an immunoassay) analyzes the trapped material at a defined sampling interval (e.g., every 1.5 hours). All ADSs under development have a way of alerting authorities of a positive signal. The result is an approximate real-time detection and alerting system.
One type of ADS, the Biohazard Detection System (BDS), was developed under contract with the U.S. Postal Service (USPS) specifically to detect aerosolized Bacillus anthracis spores. USPS plans to install BDS in approximately 300 mail processing and distribution centers (PDCs) across the United States. PDCs have high-speed mail-handling equipment that can aerosolize B. anthracis spores sent through the mail, as demonstrated during the 2001 anthrax attacks. USPS will install BDS devices on or near key equipment that processes incoming mail (e.g., advanced facer-canceller system machines). Identification of aerosolized B. anthracis spores in an air sample is necessary for prompt on-site decontamination of workers and subsequent postexposure prophylaxis (PEP) before the onset of symptoms and to interrupt the flow of contaminated letters or packages into the postal stream.
This report provides voluntary guidance for employers, state and local health departments, emergency responders, hospitals, health-care providers, and others preparing to use an ADS in a workplace with machinery or production facilities that might aerosolize B. anthracis spores mechanically.
Characteristics of Anthrax
Anthrax is a zoonotic disease caused by the spore-forming bacterium Bacillus anthracis. B. anthracis spores remain viable in the environment for years, representing a potential source of infection. Anthrax occurs in humans in three clinical forms: inhalational, gastrointestinal, and cutaneous. Inhalational anthrax results from aerosolization of B. anthracis spores through industrial processing or intentional release. Gastrointestinal or oropharyngeal forms of the disease result from ingestion of infected undercooked or raw meat. Cutaneous anthrax is the most common type of naturally acquired anthrax infection and usually occurs after skin contact with contaminated products from infected animals. Historically, the case-fatality rate for cutaneous anthrax has been <1% with antibiotic treatment and 20% without antibiotic treatment (2--4). Case-fatality rates for inhalational anthrax are high, even with appropriate antibiotics and supportive care (5). Among the 18 cases of inhalational anthrax identified in the United States during the 20th century, the overall case-fatality rate was >75%. After the biologic terrorism attack in fall 2001 in which B. anthracis spores were released through the mail, the case-fatality rate for patients with inhalational anthrax was 45% (5 of 11 cases) (5,6). The incubation period for anthrax is usually <2 weeks; however, because of spore dormancy and slow clearance from the lungs, the incubation period for inhalational anthrax can be prolonged for months. This phenomenon of delayed onset has not been recognized for cutaneous or gastrointestinal exposures. Discharges from cutaneous lesions are potentially infectious, but person-to-person transmission has been reported rarely. Person-to-person transmission of inhalational anthrax has not been documented.
B. anthracis is one of the biologic agents most likely to be used as a weapon because 1) its spores are highly stable; 2) the spores can infect through the respiratory route; and 3) the resulting inhalational disease has a high case-fatality rate. In 1979 an unintentional release of B. anthracis spores from a military microbiology facility in the former Soviet Union resulted in 69 deaths (7). The anthrax outbreak after B. anthracis spores were distributed through the U.S. mail system in 2001 further underscores the dangers of this organism as a terrorist threat (6).
After a terrorist attack, exposures to B. anthracis spores can occur through primary and secondary aerosols. Primary aerosols are dispersions of particles in air resulting from a biologic agent's initial release, whether through a disseminating device or through handling of an agent-containing package (e.g., in mechanical processing of mail). Secondary aerosols result from disruption and resuspension of settled particles. Through agglomeration (to other spores or debris) or other changes, these settled particles might not retain the characteristics of the original material (8); consequently, resuspension can result in larger diameter particle aerosols and lower airborne concentrations, both of which decrease the risk for exposure when compared with primary aerosols.
Particle sizes of primary and secondary aerosols vary. Airborne particles <100 µm in size compose an aerosol, whereas particles >100 µm settle relatively quickly (8). Typical room air velocities exceed the settling velocities of extremely small particles (i.e., approximately 5 µm in diameter), and such particles therefore tend to remain airborne for prolonged periods (and can travel farther) before impacting or settling on a surface. Particles composed of single spores or small clusters of spores have diameters of a few micrometers (e.g., 5--10 µm) and move with general air-flow patterns without rapid settling. Resuspension of settled particles depends on such factors as particle size and the type of surface on which the particles settle. Although resuspension of certain settled particles requires substantial amounts of energy, lower energy activities (e.g., paper handling, foot traffic, mail handling, and patting of chairs) can reaerosolize settled B. anthracis spores (9,10). The clinical and epidemiologic presentations of anthrax after an intentional release vary by the population targeted, the characteristics of the spores, the mode and source of exposure, and other characteristics.
Response and Consequence Management Planning
After an ADS is installed, a positive signal indicating possible presence of a biologic agent requires a coordinated, swift, and effective response. Therefore, an ADS should only be installed if
Every employer who deploys an ADS should develop detailed plans for responding to a positive signal (Box 1). Responding to ADS detection of B. anthracis involves coordinating responses with community partners and should include drills and exercises with these partners. Response planning should involve the following entities:
When a positive ADS signal occurs,
Management and Decontamination of Workers Potentially Exposed to B. anthracis
Every employer who uses an ADS device is responsible for coordinating in advance personal decontamination procedures through agreements with collaborating partners (e.g., EMS or public health agencies). During pre-event planning, the employer should work with local first responders to ensure decontamination activities will be performed appropriately and in a timely manner.
Persons in a workplace containing an ADS device face three key exposure pathways of concern: 1) aerosolization; 2) direct contamination of skin, outer layers of clothing, and workplace surfaces; and 3) indirect contamination of a vehicle or home by spores transported by clothing or exposed skin. The occurrence of inhalational and cutaneous anthrax among postal workers during 2001 underscores the importance of addressing the first two exposure pathways. Limited information is available about the extent and likelihood of risk from off-site contamination; during the 2001 anthrax outbreak, this risk appeared minimal. Personal decontamination is intended to minimize the risk of off-site contamination and to prevent cutaneous anthrax; prevention of inhalational anthrax is addressed by PEP.
Potential for Transporting Contamination Off-Site
Home contamination from work-contaminated clothing has been well-documented for a number of substances (11). A 1995 review by CDC's National Institute for Occupational Safety and Health (NIOSH) documented cases in which substances were brought home inadvertently on work clothing. The majority involved such substances as lead, asbestos, beryllium, pesticides, and other chemicals in industrial, construction, agriculture, or cottage industry settings (11); two cases involved infectious agents. A task force identified critical gaps in knowledge regarding the magnitude of take-home exposures and their potential health consequences (12).
Minimal information exists about take-home exposures associated with B. anthracis. The only known cases of anthrax among family members of exposed workers are two cutaneous cases from the early 1900s involving spouses of wool sorters employed at English textile operations (13). In a 1978 naturally occurring outbreak of anthrax associated with a textile operation in North Carolina, one of four vacuum cleaner dust samples from the homes of textile-mill workers was positive for B. anthracis, indicating that workers carried spores home on their clothing. However, no cases of anthrax were reported among workers' families (14).
Although take-home exposure was not systematically studied during the 2001 outbreaks associated with the release of weaponized B. anthracis, the experiences of those cases might be relevant to ADS use. No anthrax cases occurred among family members of postal workers during the 2001 outbreaks, indicating that risk was low for inhalational and cutaneous anthrax for family members from contaminated clothing. The 2001 anthrax cases in media offices provided evidence that home contamination could occur from contaminated letters opened at work. For example, environmental surface swab samples were positive in residences of certain persons who came into direct physical contact with opened, contaminated letters in New York City [personal communication, Jeanine Prud'homme, M.S., New York City Department of Health and Mental Hygiene, New York, New York, February 14, 2004]. No environmental sampling was reported for possible home contamination among Capitol Hill workers associated with the opened letter to Senator Tom Daschle of South Dakota. However, off-site contamination by equipment and clothing occurred when members of the U.S. Capitol Police Hazardous Device Unit who had responded to the letter returned to their office. Environmental sampling located contamination in vehicles and office-space surfaces where equipment was handled. No anthrax cases were reported among family members from home contamination in any of these instances.
To prevent or minimize exposure to workers' families, occupational health standards and guidelines typically call for basic hygiene practices (e.g., leaving work clothing and shoes at the job site, washing, and, in certain cases, showering after work). Such precautions traditionally target employees who routinely work with harmful substances (e.g., lead and asbestos) and who can reduce take-home exposures to these occupational contaminants (15). Basic hygiene recommendations also exist for managing potential exposures after a B. anthracis attack against a civilian population. The current consensus statement recommends that "any person coming in direct physical contact with a substance alleged to be containing B. anthracis should thoroughly wash the exposed skin and articles of clothing with soap and water" (16). Although the risk of cutaneous anthrax from off-site transport appears low, because of gaps in knowledge about this risk, a positive signal from an ADS should elicit a conservative approach to personal decontamination (Box 2).
Recommendations for Evacuation and Personal Decontamination
The primary goal of using an ADS is to prevent inhalational anthrax through early recognition of and response to an exposure situation, including early initiation of PEP. Aerosolization or direct physical contact can result in deposition of spores on the outerwear of employees and subsequent transport off site. Because limited scientific data exist regarding B. anthracis and personal decontamination, these recommendations are based primarily on available information; general industrial-hygiene concepts, principles, and practices; analogy to other contaminants and industrial settings; and a prudent public health approach. These recommendations might change as information regarding the efficacy of control systems, decontamination methods, and safe work practices becomes available.
Employers, in consultation with first responders and public health departments, should determine exit routes and places of refuge. An outdoor refuge location might be considered but can be problematic because of weather, security, or other concerns. A physically separate building or space inside the potentially contaminated building might also merit consideration, by using the following criteria:
Workers should be categorized into three groups for evacuation and decontamination procedures (Box 2). Group 1 includes those workers who did not enter the production area containing the ADS device during the sampling and testing period (e.g., 1.5 hours) before the positive ADS signal and whose work locations do not share an HVAC system with the production area experiencing the positive signal. Group 2 includes all workers who were present in the production area containing the ADS device during the sampling and testing period before the positive ADS signal or who are located in any space that shares an HVAC system with the production area experiencing the positive signal. Group 3 includes all workers identified in advance as particularly at risk of exposure to a higher concentration of deposited spores as a result of direct physical contact with aerosol-generating equipment. Workers in these groups should be evacuated and decontaminated as follows:
Logistical considerations for decontamination include the following:
Other general considerations include the following:
Laboratory Evaluation of a Positive ADS Signal
A well-designed ADS has four attributes: 1) a stand-alone and contained configuration; 2) ability to collect a substantial volume of sample; 3) use of a detection technology requiring minimal manual attention; and 4) control procedures to ensure adequate assay performance, including lack of inhibition and reagent stability. Ideally, the assay used in an ADS will have extremely high positive and negative predictive values. Key factors for ensuring accurate and consistent results from ADS devices are development and implementation of maintenance plans with rigid quality-assurance controls. These plans should describe specific policies and procedures for use and maintenance of an ADS. If all these criteria are met, a high level of confidence can be ensured that a positive ADS signal represents a true B. anthracis aerosolization event.
Nevertheless, a positive ADS signal should be confirmed by an LRN laboratory using both PCR assay and culture. Policies and procedures for specimen management, including chain of custody, should be arranged in advance. Finally, persons should be identified and trained who can ensure correct collection and transport of the ADS specimen to the LRN laboratory.
Initial Environmental Evaluation
Environmental sampling in coordination with public health and law enforcement immediately after an ADS signal might be necessary to address both public health and law enforcement goals. The primary law enforcement goal is to assist the criminal investigation by finding the source of contamination. The immediate public health goal is to determine who is in need of PEP (in addition to those who were either in the production area or in a location that shared air-handling with the production area). For example, if a letter causes a positive ADS signal at a PDC, it would be important to ascertain which employees, if any, at other facilities through which the letter has passed, should be considered for PEP. Sampling the machine where the ADS is located to confirm a positive ADS signal might also be appropriate. Information about the extent of contamination at the facility is important but is a less-immediate need. Nasal swabs of potentially exposed workers to test for B. anthracis are not recommended.
General guidance, criteria, and recommendations for sampling of B. anthracis-contaminated areas are available elsewhere (24). Planning for environmental sampling activities before activating an ADS is necessary to ensure that
Postexposure Prophylaxis and Follow-Up
Inhaled spores can remain dormant in the lungs or lymphatic system for weeks to months before germination (27,28). After germination in alveolar macrophages, vegetative organisms can replicate and cause symptomatic disease. Reported incubation periods have ranged from 1 to 43 days after initial exposure but can be affected by the dose of B. anthracis inhaled and the use of antibiotics (1,5). Delayed disease onset is not known to occur with cutaneous or gastrointestinal exposures.
Two methods exist to protect against B. anthracis after the spores have reached the vegetative state. The first is to have adequate levels of antibiotics in the bloodstream to kill vegetative bacteria. The second is to have adequate anti-B. anthracis antibodies in the bloodstream when vegetative bacteria appear. Two U.S. national advisory bodies have considered PEP strategies for preventing inhalational anthrax among persons exposed to aerosolized spores. Both groups, the Advisory Committee on Immunization Practices (ACIP) and the Johns Hopkins Working Group on Civilian Biodefense, concluded that on the basis of available data, the best means for preventing inhalational anthrax is prolonged antibiotic therapy in conjunction with anthrax vaccination (29,30). The 2002 Institute of Medicine report on anthrax vaccine safety and efficacy also concluded that on the basis of limited animal studies, anthrax vaccine administered in combination with antibiotics after exposure to B. anthracis spores might help prevent development of inhalational anthrax (31).
In PEP, antibiotics are initiated as soon as possible after actual or suspected inhalation of B. anthracis spores and anthrax vaccination is started to stimulate production of protective antibodies, so that by the time exposed persons complete their course of antibiotics, they will have sufficient antibodies to protect them against residual spores. Although the effect of delayed PEP or treatment on survival can only be approximated, mathematical models indicate that for each day PEP is delayed after an aerosol exposure, the case-fatality rate can increase by 5%--10% (32).
The available anthrax vaccine, BioThrax [BioPort Corporation, Lansing, Michigan], is not licensed for PEP, for use as a 3-dose PEP regimen, or for use in children. Therefore, a postexposure regimen of antibiotics and anthrax vaccine can only be administered under an Investigational New Drug (IND) application as part of an emergency-health intervention. If the vaccine is released for use in emergency situations, CDC will provide the IND protocol for delivery and use in collaboration with state and local health departments. In conjunction with the 3-dose regimen of vaccine, 60 days of selected oral antibiotics (i.e., ciprofloxacin, doxycycline, or amoxicillin) should be administered to persons potentially exposed to aerosolized B. anthracis spores. The Food and Drug Administration has approved ciprofloxacin and doxycycline for use as PEP against anthrax. When no information is available about the antimicrobial susceptibility of the implicated strain of B. anthracis, initial PEP with ciprofloxacin or doxycycline is recommended for adults and children (33--35). Although fluoroquinolones and tetracyclines are not recommended as first-choice drugs among children because of adverse effects, these concerns might be outweighed by the need for early treatment of pregnant women and children exposed to B. anthracis after a terrorist attack. As soon as the organism's susceptibility to penicillin has been confirmed, prophylactic therapy for children and pregnant women should be changed to oral amoxicillin. B. anthracis is not susceptible to cephalosporins and trimethoprim-sulfamethoxazole; therefore, these agents should not be used for prophylaxis (33--35).
The incubation period to onset of clinical symptoms for inhalational anthrax can be as short as 24 hours (5). Therefore, after a positive ADS signal, confirmation should be obtained from an LRN laboratory and PEP started as soon as possible, preferably within 15 hours after onset of the collection period that yielded the positive signal. Additional data are needed on outcomes from inhalational anthrax where onsets of PEP varied after exposure to B. anthracis.
Pre-event planning should include measures to ensure timely transport and receipt of an LRN laboratory result. The decision to begin PEP should be made on the basis of risk for B. anthracis exposure, including likelihood of aerosol exposure to the powder (1), threat assessment in conjunction with law enforcement, validity of preliminary laboratory testing of the suspicious substance, and logistics of initiating an intervention. Epidemiologic and laboratory test data might indicate that certain persons started on PEP were not exposed and that PEP can be discontinued. Persons who potentially have been exposed to B. anthracis should be followed medically for signs and symptoms of disease; in addition, severe adverse events associated with postexposure antibiotics or vaccine should be identified and reported to local health authorities. PEP should proceed as follows:
Every employer who uses an ADS device is responsible for coordinating in advance PEP distribution procedures through agreements with collaborating partners, including public health authorities. Planning should include arrangements for rapid access to an initial 3-day course of antibiotics to ensure that prophylaxis can begin as soon as possible after B. anthracis exposure has been confirmed by an LRN PCR assay. Antibiotics deployed from the Strategic National Stockpile (SNS) can take 12 hours to deliver after the federal decision to deploy.
Alternatives for securing an initial 3-day course of antibiotics near the PDC site might include maintaining an inventory on-site or making arrangements with local pharmacies, medical centers, or hospitals to maintain sufficient inventories on the employers' behalf. Which of these options is most appropriate will depend on local conditions and capacities (e.g., the number of potentially affected employees, logistics associated with release and recall of employees, and medical resources in the area). When addressing this concern, employers are strongly encouraged to work with their local public health departments to ensure that quantity and dosage requirements are met and that plans for rapid access and delivery are established and practiced through periodic drills.
Devices that detect agents of terrorism in the environment have the potential to decrease the time required to detect a terrorist event and therefore improve the potential for preventing illness and interrupting further exposure and contamination. In multiple U.S. cities, environmental detection systems (e.g., BioWatch) have been implemented to assist in detecting releases. These systems typically work by employing air-sampling filters, with the filter needing to be removed periodically and sent to a laboratory for testing. Use of an ADS, in which sampled air is tested internally, can decrease the lag time between release of an agent and its detection.
Although environmental detection devices are being deployed, the need to better assess their effectiveness should be considered, including studies to evaluate the benefit of these approaches in preventing terrorism-related illness. CDC will work with employers and state and local public health agencies to identify opportunities to do this. These recommendations will be revised and updated as new information becomes available. CDC will also continue to collaborate with employers and state and local public health agencies to ensure a swift and effective response to positive ADS signals.
The following organizations and persons reviewed drafts of this report and provided valuable comments: United States Postal Service; American Postal Workers Union; National Postal Mail Handlers Union; National Association of Letter Carriers; Association of State and Territorial Health Officials (ASTHO); National Association of City and County Health Officials (NACCHO); Council of State and Territorial Epidemiologists (CSTE); Association of Public Health Laboratories (APHL); Charles A. Schable, M.D., Bioterrorism Preparedness and Response Program, National Center for Infectious Diseases, CDC; Lisa A. Dillard, Division of Emergency Operations, Office for Terrorism Preparedness and Emergency Response, CDC; Eddy A. Bresnitz, M.D., New Jersey Department of Health and Senior Services, Trenton, New Jersey; Susan Allan, M.D., J.D., Arlington County Department of Human Services, Arlington, Virginia; James R. Miller, M.D., New York State Department of Health, Albany, New York; Dorothy Canter, Ph.D., U.S. Environmental Protection Agency, Washington, D.C.
* LRN laboratories are those that participate in a network of public health laboratories meeting criteria specified by CDC in collaboration with partners. Additional information is available at http://www.bt.cdc.gov/lrn/factsheet.asp.
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