Fumigation of high-containment microbiology facilities is an international requirement and in the UnitedKingdom this process is still commonly undertaken using formaldehyde vaporization. Formaldehyde usage is simple and inexpensive, but concerns exist over its toxicity and carcinogenicity. Alternative fumigants exist, although independent, parallel comparison of these substances is limited. This study determined the level of biocidal efficacy achievable with formaldehyde and compared this with other commonly used fumigants. Three different hydrogen peroxide-based fumigation systems were evaluated (two vapor and one dry-mist methods), along with true gas systems employing ozone and chlorine dioxide. A range of challenge microorganisms was used at different room locations to assess the efficacy, usability, and safety of the fumigation equipment. These microorganisms included Geobacillus stearothermophilus, Clostridium difficile, Mycobacterium fortuitum, and Vaccinia virus. Only chlorine dioxide and formaldehyde fumigants gave consistently high levels of antimicrobial efficacy across all bacterial challenge tests (typically greater than a 5-log reduction). All systems performed similarly against Vaccinia virus, but variable results were noted for Geobacillus, C. difficile, and M. fortuitum for the hydrogen peroxide-and ozone-based systems. The study also revealed inconsistencies in system reliability and reproducibility, with all fumigant systems aborting midcycle on at least one occasion. In contrast, formaldehyde fumigation was confirmed as extremely reliable, largely because of its simplicity (liquid plus hot plate). All the fumigants tested have UK workplace exposure limits of 2 ppm or less, yet residual fumigant was detected for the formaldehyde and hydrogen peroxide systems following cycle completion, even after room aeration.
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