Results after a chemical decontamination cycle performed with vaporized H2O2

Abstract

This article discusses the challenge of the unexpected growth of a positive biological indicator in a chemical decontamination cycle. Specific features to be considered regarding biological indicators used for the validation of decontamination cycles are presented. Some practical solutions are suggested to avoid the risks related to false positives.

Keywords: chemical bio-decontamination, hydrogen peroxide, biological indicators, false positives,
validation of decontamination cycles

BIOLOGICAL INDICATORS

An undesirable event that might have happened to many, is the unexpected growth of a biological indicator (BI) at the end of a decontamination cycle when, a positive result is highly improbable. How best to face this situation? If a single BI were used to provide answers for each position, a deep analysis of the failing cause would not be possible, thus maintaining the dilemma: “is it an inadequate cycle or a defective BI?” In that situation, even a statistical analysis would be unfeasible. However, the application of, at least, two or three BIs per point might help overcoming the difficulty.

HYDROGEN PEROXIDE

Biological indicators produced and used to validate a chemical decontamination cycle, as with hydrogen peroxide, have specific features. Being a surface agent, the vaporized hydrogen peroxide is not able to penetrate the deeper layers of the material unless the indicators form a monolayer of spores deposited on the chosen substrate. This way, the biological indicator spores on the substrate are easily reachable by the chemical agent making possible to assess its microbiological effectiveness. Otherwise, the peroxide would be effective only on the top layer of spores with the risk of false positives at the end of the incubation period.

BIS PREPARATION

The inaccurate preparation of BIs or inappropriate conservation storage conditions could entail the deposit of accumulated spores unreachable by the hydrogen peroxide. Therefore, the application of more than one BI per position becomes beneficial to help determine the cause of a positive output and to evaluate the reduction of the microbial level reached. For example, considering a position where 3 (three) BIs had been placed and supposing that the result obtained was: + – – , the challenge in this case lies on the attribution of the positive result to the BI rather than to the cycle conditions.