Lisa S. Smith

Quantitative Method To Determine Sporicidal Decontamination of Building Surfaces by Gaseous Fumigants, and Issues Related to Laboratory-Scale Studies

ABSTRACT Chlorine dioxide gas and vaporous hydrogen peroxide sterilant have been used in the cleanup of building interiors contaminated with spores of Bacillus anthracis. A systematic study, in collaboration with the U.S. Environmental Protection Agency, was jointly undertaken by the U.S. Army-Edgewood Chemical Biological Center to determine the sporicidal efficacies of these two fumigants on six building structural materials: carpet, ceiling tile, unpainted cinder block, painted I-beam steel, painted wallboard, and unpainted pinewood. Critical issues related to high-throughput sample processing and spore recovery from porous and nonporous surfaces included (i) the extraction of spores from complex building materials, (ii) the effects of titer challenge levels on fumigant efficacy, and (iii) the impact of bioburden inclusion on spore recovery from surfaces and spore inactivation. Small pieces (1.3 by 1.3 cm of carpet, ceiling tile, wallboard, I-beam steel, and pinewood and 2.5 by 1.3 cm for cinder block) of the materials were inoculated with an aliquot of 50 μl containing the target number (1 × 106, 1 × 107, or 1 × 108) of avirulent spores of B. anthracis NNR1Δ1. The aliquot was dried overnight in a biosafety cabinet, and the spores were extracted by a combination of a 10-min sonication and a 2-min vortexing using 0.5% buffered peptone water as the recovery medium. No statistically significant drop in the kill efficacies of the fumigants was observed when the spore challenge level was increased from 6 log units to 8 log units, even though a general trend toward inhibition of fumigant efficacy was evident. The organic burden (0 to 5%) in the spore inoculum resulted in a statistically significant drop in spore recovery (at the 2 or 5% level). The effect on spore killing was a function of the organic bioburden amount and the material type. In summary, a high-throughput quantitative method was developed for determining the efficacies of fumigants, and the spore recoveries from five porous materials and one nonporous material ranged between 20 and 80%.

Disinfection of Acinetobacter baumannii-contaminated surfaces relevant to medical treatment facilities with ultraviolet C light.

The efficacy of ultraviolet C (UVC) light (100-280 nm) in the decontamination of three hospital-related surfaces, namely, unpainted/painted aluminum (bed railings), stainless steel (operating tables), and scrubs (laboratory coats), was investigated. Acinetobacter baumannii cells were inoculated (10(5) or 10(3) cells) on small coupons and dried overnight in a class II biosafety cabinet. Drying resulted in < or =50% loss of viability. The UVC fluence of 90 J/m2 was observed to be very effective in the decontamination of cells from all metal coupon surfaces (complete killing). However, the same fluence was ineffective in the decontamination of scrubs. The effectiveness of two other common disinfection practices, that is, 15 minutes of boiling or spraying with 70% ethanol, was investigated for the scrubs. Although ethanol treatment was ineffective, the boiling treatment was very effective (complete killing). These results establish that metal surfaces can be decontaminated with UVC irradiation and boiling treatment is effective for scrub decontamination.

Systematic evaluation of the efficacy of chlorine dioxide in decontamination of building interior surfaces contaminated with anthrax spores.

ABSTRACT Efficacy of chlorine dioxide (CD) gas generated by two distinct generation systems, Sabre (wet system with gas generated in water) and ClorDiSys (dry system with gas generated in air), was evaluated for inactivation of Bacillus anthracis spores on six building interior surfaces. The six building materials included carpet, acoustic ceiling tile, unpainted cinder block, painted I-beam steel, painted wallboard, and unpainted pinewood. There was no statistically significant difference in the data due to the CD generation technology at a 95% confidence level. Note that a common method of CD gas measurement was used for both wet and dry CD generation types. Doses generated by combinations of different concentrations of CD gas (500, 1,000, 1,500, or 3,000 parts per million of volume [ppmv]) and exposure times (ranging between 0.5 and 12 h) were used to evaluate the relative role of fumigant exposure period and total dose in the decontamination of building surfaces. The results showed that the time required to achieve at least a 6-log reduction in viable spores is clearly a function of the material type on which the spores are inoculated. The wood and cinder block coupons required a longer exposure time to achieve a 6-log reduction. The only material showing a clear statistical difference in rate of decay of viable spores as a function of concentration was cinder block. For all other materials, the profile of spore kill (i.e., change in number of viable spores with exposure time) was not dependent upon fumigant concentration (500 to 3,000 ppmv). The CD dose required for complete spore kill on biological indicators (typically, 1E6 spores of Bacillus atrophaeus on stainless steel) was significantly less than that required for decontamination of most of the building materials tested.

The Sporicidal Potency of Bioxy Formulations in Decontaminating Bio-Warfare Agents

Biological terrorism has become a major concern worldwide since the 2001 mailing of anthrax spore-tainted letters. Bacillus globigii has been used as one of surrogates for the pathogenic Bacillus anthracis, the causative agent of anthrax. Many chemical compounds have been used to decontaminate anthrax spores such as chlorine, peroxide, N-chloro derivatives of ammonia, and chlorine dioxide. However, some of these compounds are not environmentally-friendly, as they are either corrosive to surfaces or toxic to humans. We propose Bioxy formulations which are powdered concentrated products that generate peracetic acid at near-neutral pH when dissolved in water. Solutions derived from such formulations are very effective virucidal, bactericidal, fungicidal and tuberculocidal compounds. Moreover, they are safe on various metallic and polymeric surfaces with strong wetting and penetrating abilities. In this study, we demonstrate that a 2% concentration of “Bioxy Enviro” is a highly effective sporicidal formulation, since >5-6 logs reduction in the number of viable spores of Bacillus globigii within 1030-min exposure was observed. Furthermore, when DeconGel was reformulated with Bioxy solution at 2%, the waste generation was minimized and the decontamination in hard to reach places was maximized, since >5-6 log spore kill of Bacillus anthracis was observed on four surfaces. Correspondence to: Vipin K. Rastogi, BioDefense Team, R&T Directorate, U.S. Army Edgewood Chemical Biological Center, Aberdeen Proving Grounds, Maryland 21010, USA, E-mail: vipin.k.rastogi.civ@mail.mil