Anthrax

Decontamination of Persons Exposed to Anthrax

According to guidelines from the Association for Professionals in Infection Control and Epidemiology (APIC) and the CDC (see References: 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 (see References: 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 (see References: Martin 2010: Anthrax as an agent of bioterrorism). A process for determining what level of contamination is acceptable has been proposed as follows (see References: 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 (see References: 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 (see References: Spotts Whitney 2003). In addition, reasonable standards for cleanup effectiveness remain to be established (see References: Canter 2005). Paraformaldehyde (with Bacillus 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 (see References: 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 (see References: 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 (see References: Black 2008). A combination of high temperature (90°C to 95°C) and hydrogen peroxide also could be used to inactivate B anthracis spores (see References: Xu 2008).