Environmental Testing and Decontamination

Last updated May 25, 2011

Note: This document is best viewed with Internet Explorer for both format and function.

Environmental Testing as a Detection Tool
Environmental Testing Following a Release
Decontamination of Persons Exposed to Anthrax
Decontamination of Environment
Gaps in Decontamination Policy and Practice
Bibliography

Environmental Testing as a Detection Tool

Autonomous detection systems (ADSs) have been developed to detect B anthracis spores in the environment (indoor or outdoor) as the first signal of an aerosol release. Examples include the following:

Biohazard Detection System (BDS): The BDS is a fully automated air-sampling system consisting of an aerosol collector, PCR cartridge based on Cepheid GeneXpert technology, and controller computer. It has been deployed in mail processing and distribution centers across the United States. Positive BDS signals will be confirmed by an LRN reference or national laboratory (CDC 2004: Responding to detection of aerosolized Bacillus anthracis by autonomous detection systems in the workplace, NALC).

According to the CDC guidelines, when a positive BDS signal occurs, the following immediate response is appropriate:

Stop work activities.
Stop and secure any potential aerosol-generating equipment.
Turn off heating, ventilation, and air conditioning (HVAC) units serving the production or processing area (leave local exhaust ventilation on machines turned on).
Notify local and federal law enforcement and public health officials.
Immediately account for all workers to ensure their evacuation.
Gather personal identification and contact information.

Depending on the level of potential exposure, decontamination of employees (with removal of clothing and washing exposed areas or showering at the site) may be necessary.
The decision to begin postexposure antibiotic prophylaxis should be made on the basis of risk of exposure, threat assessment, validity of preliminary laboratory testing, and logistics of initiating an intervention.

Autonomous Pathogen Detection System (APDS): Consists of an aerosol collector, flow-through PCR subsystem with sequential injection analysis, and a multianalyte flow-cytometry subsystem for PCR product detection (Hindson 2004, LLNL 2002).
Anthrax Smoke Detector (ASD): An automated system designed by the National Aeronautics and Space Administration (NASA) to detect changes in airborne bacterial spore concentrations, including spores of B anthracis. The system measures dipicolinic acid (DPA), a chemical marker of bacterial spores. The ASD is intended as a relatively low-cost screening tool and requires that positive signals must be confirmed by B anthracis–specific assays (Lester 2004). A recent test revealed that the device had a detection limit of 16 spores/L when 250 L of air was sampled (Yung 2007).
Handheld Advanced Nucleic Acid Analyzer (HANAA). A real-time PCR analyzer using a miniaturized thermal cycling process (LLNL 2002).
Mobile laboratory systems (used primarily by the military): Automatic Biological Agent Testing System (ABATS), PortalShield, Joint Biological Point Detection System (JBPDS), and Biological Integrated Detection System (BIDS) (Fitch 2003).

Environmental Testing Following a Release

Environmental testing for B anthracis should be conducted by public health or law enforcement officials in the context of an epidemiologic or criminal investigation. Sampling should be guided by available epidemiologic data whenever possible (Teshale 2002) and should be performed in accordance with the most recently recommended sampling methods and protocols.

Criteria for performing directed sampling of environmental surfaces as specified by the CDC include the following (CDC 2001: Interim guidelines for investigation of and response to Bacillus anthracis exposures):

To identify a site or source of B anthracis exposure that resulted in a case(s) of anthrax
To trace the route of an exposure vehicle (eg, powder-containing letter)
To obtain the B anthracis strain when isolates from patients are not available
To guide cleanup activities in a contaminated area or building
To assess biosafety procedures in laboratories processing B anthracis specimens

ASTM International (formerly the American Society for Testing and Material Standards), a voluntary standards development organization, has published a standard on practices for "bulk sample collection and swab sample collection of visible powders suspected of being biological agents from nonporous surfaces." A recent collaborative study validated the methods in the standard and showed that high levels of B anthracis and B thuringiensis spores can be recovered from surfaces by both dry and wet swab sampling methods (Locascio 2007).

Environmental sampling of a US postal facility in Washington, DC, during the 2001 anthrax outbreak demonstrated the following (Sanderson 2002):

Sampling using wipes or HEPA vacuum socks provided a better yield than sampling with wet or dry swabs.
Dry swabs generally should not be used for sampling, since yields are so low.
Wet swabs may be useful in certain situations (eg, crevices, inside machinery, other areas difficult to reach by wipe or HEPA vacuum samples).
Wipes are preferable for sampling areas with light dust.
HEPA vacuum socks should be used to sample surfaces with heavy dust.

One study evaluated four swab materials (cotton, macrofoam, polyester, and rayon) and methods of processing to determine optimal spore recovery. Results demonstrated that premoistened cotton and macrofoam swabs were the most efficient (Rose 2004). In a study of polyester-rayon wipes, sonication extraction improved recovery of spores from wipes used for cleaning surfaces. The wipe recovery quantitative limits of detection were estimated at 90 CFU per unit of stainless steel surface area and 105 CFU per unit of painted wallboard (Brown 2007). In a study of recovery efficiencies of anthrax spores, contact plates performed better than other methods for flat, nonporous, nonabsorbent surfaces, with recovery rates of 28% to 54%. Contact plates also performed the best on flat, porous, absorbent surfaces, although recoveries were low (less than 7%). For moistened devices (wipes, swabs, and sample collection and recovery devices), wipes were generally the best (Frawley 2008).

Official procedures for testing food and water have not been published, but protocols reportedly have been developed by USAMRIID (Higgins 1999) and are under development elsewhere.

A number of commercial test kits for environmental sampling are available. A study of three such systems, BioThreat Alert (BTA), BioWarfare Agent Detection Devices (BADD), and SMART II, found a minimum detection limit of 10⁵ spores, far above the level of 10² spores desired by first-responders (King 2003). The specificities of these systems have not been independently evaluated.

Decontamination of Persons Exposed to Anthrax

According to guidelines from the Association for Professionals in Infection Control and Epidemiology (APIC) and the CDC (APIC/CDC 1999):

Patients should remove contaminated clothing and store in labeled, plastic bags.
Clothing should be handled as little as possible to avoid agitation.
Patients should shower thoroughly with soap and water.

Decontamination of Environments

Concerns regarding environmental contamination involve both primary and secondary aerosolization.

Primary aerosolization occurs when the spores are first made airborne. This is the period when the risk of inhalation is the greatest. The risks of primary aerosolization depend on how long spores remain airborne and how far they travel before falling to the ground or other surfaces. Meteorological conditions and aerobiological properties of the dispersed aerosol will influence the duration and scale of the risk (HPA 2007).
Secondary aerosolization involves resuspension of spores into the air after they have initially settled on environmental surfaces. The risks posed by secondary aerosolization have not been defined and are dependent on a number of variables (eg, concentration of spores in the environment, type of powder used in the suspension, level of activity in the contaminated area, type of environmental surface involved).

Determining the extent of remediation necessary for contaminated environments remains controversial. Ideally, the remediation effort should be timely and cost-effective and protect the public health (Martin 2010: Anthrax as an agent of bioterrorism). A process for determining what level of contamination is acceptable has been proposed as follows (Price 2009):

Decide on the level of risk that is acceptable.
Convert the risk to an airborne spore concentration, via an assumed dose-response curve.
Convert the airborne spore concentration to a surface concentration, using an assumed resuspension rate.
Convert the surface concentration to a probability that any single sample is positive for B anthracis, using a sampling effectiveness curve.
Find the number of samples needed (for the single-sample probability above) such that if all the samples are negative, then the building or area is "safe" with a specified certainty.

During the 2001 anthrax attacks, the Environmental Protection Agency (EPA) assessed the potential for secondary aerosolization inside the Hart office building by conducting environmental sampling under semiquiescent (minimal activity) conditions and under simulated active office conditions (Weis 2002).

Findings demonstrated that viable B anthracis spores could be reaerosolized during simulated active office conditions.
CFU levels detected through air sampling demonstrated as much as a 65-fold increase under the active office conditions compared with the semiquiescent conditions.
These findings support the need for environmental decontamination and protection of decontamination workers following release of high concentrations of anthrax spores into indoor environments.

During the 2001 US anthrax outbreak, several buildings underwent environmental decontamination to eliminate the risk of potential secondary aerosolization. In the setting of a bioterrorism attack, the EPA is charged with directing cleanup activities and providing the necessary technical expertise to guide such efforts. The EPA used several methods and technologies to decontaminate buildings during the 2001 outbreak (ie, chlorine dioxide, decontamination foam, ethylene oxide). Cleanup plans generally involve the following:

Assess the size and type of the potentially contaminated area.
Assess how the contamination was delivered.
Conduct sampling to determine the level of contamination.
Determine the microbiocide to be used and methods of delivery for decontamination.
Carry out decontamination procedures.
Conduct environmental sampling after decontamination to ensure that anthrax spores have been removed or killed and that the area is safe to reoccupy.

Until the recent anthrax attack, experience with decontamination of buildings after contamination with weapons-grade anthrax spores was limited. Questions regarding the best methods for decontamination in such situations still remain (Spotts Whitney 2003). In addition, reasonable standards for cleanup effectiveness remain to be established (Canter 2005). Paraformaldehyde (with B subtilis as the indicator) has been used to decontaminate laboratories.

The chlorine dioxide fumigation approach used after the 2001 postal anthrax attacks is expensive and can preclude reoccupation of contaminated buildings for many years. Wein and colleagues compared this approach to a strategy of HEPA vacuuming, HEPA air cleaners, and vaccination of building occupants (Wein 2005). They found in a simulated outdoor release in lower Manhattan that the HEPA/vaccine method would require less time, cost less, and reduce solid waste problems associated with disposal of contaminated carpets and upholstery. However, the details of the massive cleanup operation modeled by the study depend on many factors related to the attack itself, which obviously cannot be accurately predicted. Furthermore, vaccination of reoccupants may not be a practical or acceptable approach.

Vaporized hydrogen peroxide (Vaprox) may represent a new method for decontamination of buildings or other enclosed areas. The EPA has granted vaporized hydrogen peroxide an emergency exemption for the specific use of anthrax decontamination. Available data showed that the gas significantly reduced bacterial spore populations under specific conditions (EPA 2007).

Several hypochlorite-containing household products on the market were found to be effective in decontaminating milk or similar food products contaminated by spores to allow safe disposal (Black 2008). A combination of high temperature (90°C to 95°C) and hydrogen peroxide also could be used to inactivate B anthracis spores (Xu 2008).

Gaps in Decontamination Policy and Practice

The environmental decontamination response following the 2001 postal anthrax attacks required hundreds of millions of dollars in direct costs, and some facilities were closed for more than 2 years (Franco 2010). Although the attack represents the worst case of bioterrorism in US history, it is considered to be small in scale. Recently, an analysis was undertaken to identify current gaps in decontamination policy and practice at the federal level that must be addressed to achieve a successful response following a large-scale attack. Identified gaps include:

Unclear roles and responsibilities for federal agencies involved in a decontamination response
Lack of a coordinated, sustained, and adequately funded research program for biological decontamination
Limited technologies and methods for sampling, testing, and analysis of contamination
Scientific uncertainty about biological agent properties, decontamination methods, and risks to human health
Absence of decontamination standards
Shortage of trained personnel to carry out decontamination response


Home	Mission & Activities	About Us	Your Support	Contact Us