Johannes Rauschnabel

The Influence of Humidity, Hydrogen Peroxide Concentration, and Condensation on the Inactivation of Geobacillus stearothermophilus Spores with Hydrogen Peroxide Vapor

The study presented here examined the factors influencing the effectiveness of surface decontamination with hydrogen peroxide vapor. The impact of relative humidity and hydrogen peroxide gas concentrations was investigated and compared to a dew point analysis of these various sterilant atmospheres. For this purpose, a series of different H2O2 decontamination cycles were developed and tested for antimicrobial effectiveness using biological indicators inoculated with greater than 106 spores of Geobacillus stearothermophilus. The results indicate that an increasing concentration of hydrogen peroxide in the gas phase and higher humidity levels result in a faster inactivation of the test organisms. The higher the H2O2 gas phase concentration was, the more independent the inactivation effect from the humidity level. At lower H2O2 concentrations, the same kill was achieved with higher humidity. Subvisible condensation was found to be necessary for short inactivation times, but condensation in the visible range did not further enhance the sporicidal activity. The molecular deposition of water and hydrogen peroxide on the target surface represents the determining factor for microbial inactivation, whereas the hydrogen peroxide concentration in the gas phase is of secondary importance.

Hydrogen Peroxide Vapor Penetration into Small Cavities during Low-Temperature Decontamination Cycles

IntroductionThe suitability of vapor-phase hydrogen peroxide for the decontamination of different-sized narrow cavities and complex geometrical structures were investigated in this paper.MethodsA cavity test block was used, and cavities made from different materials were tested with variable entrance heights and cavity depths. At the end of each cavity, biological indicators were exposed as a microbiological challenge for vapor-phase hydrogen peroxide penetration. Within this study, the test block with the biological indicators was subjected to different decontamination cycles in a production isolator. Inoculation level, cycle length, hydrogen peroxide, and water concentration were varied.ResultsThe ratio of cavity entrance height to depth was found to be critical for decontamination success by biological indicators exposed inside the cavities. The higher the ratio, the more spores could be inactivated. Inactivation is also effected by exposure time and hydrogen peroxide concentration.ConclusionThe results indicate that the entrance height of the cavities should not be smaller than 6 mm and the cavity depth should not exceed 30 mm. If smaller cavities cannot be avoided, high peroxide concentration (800 ppm) and prolonged cycle times were shown to significantly enhance the penetration into dead-ended cavities under diffusive conditions.