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. Articles

Methicillin resistant Staphylococcus aureus(MRSA) is an ongoing clinical problem world-wide and a recognised cause of nosocomial infection. In the UK it has been reported that approximately 100,000 patients acquire nosocomial infections per annum, of which 6000 die [1]. If MRSA survives for long periods in health-care environments, this may contribute to infection transmission from fomites. We evaluated the effect of humidity on the survival of MRSA on five different hard surfaces commonly found in health-care establishments. Adjusting the humidity of such environments may provide an inexpensive way of reducing MRSA prevalence. Tiles (1cm2) of five surface types including wood and Formica were inoculated with 5 105–5 106 ATCC EMRSA15 cells suspended in PBS with 1% BSA. EMRSA15 was chosen as it is the most common of two prevalent strains in UK hospitals. Multiple samples of each surface type were then incubated at 42%, 52% and 65% relative humidity (RH) at 23°C (room temperature). Cells from samples of each surface type were re-suspended; agar plates were inoculated and incubated overnight at 37°C and the number of colonies counted. Samples were taken every day for the first week, twice weekly for the following 2 weeks and once a week thereafter. Numbers of viable cells decreased over time from 5105–5106 at day one to below 2 104 by day 22. Minor differences in the rate of decline occurred with different humidities and surface types, generally showing a steep decline in numbers in the first 10 days and a slower decline thereafter. After 57 days numbers were less than 600 but some still persisted.