Measurement of the microbial barrier effectiveness of sterilization containers in terms of the log reduction value for prevention of nosocomial infections

Background The microbial barrier properties of 216 sterilization containers of 4 central sterile supply departments of different hospitals were measured using a microbial challenge test. Methods Uncovered thermoresistant plates filled with Sabouraud agar were placed on the base of the containers prior to sterilization. After sterilization, the containers were exposed to a defined microbial aerosol and periodic atmospheric pressure reductions of 10 to 70 hPa in an exposure chamber. After exposure and incubation of the entire containers, colony growth was registered as colony forming units (CFU) on the plates and the control plates to calculate the barrier effectiveness in terms of the logarithmic reduction value (LRV). Results Two out of 11 standard containers with paper filters and 9 out of 79 containers with textile filters showed no growth on the plates. The mean colony numbers were 222 CFU/600 cm2 (standard container with paper filter) and 209 CFU/ 600 cm2 (container with textile filter). Fourteen out of 15 containers with permanent plastic filters did not show any growth on the plates. No recontamination was observed in 18 of 111 half-size containers. The mean colony numbers of the recontaminated half-size containers were 110 (paper filter) and 34 CFU per 300 cm2 (textile filter). The LRVs of the full-size and half-size containers tested ranged between 1.08 and >4. Conclusion As shown in this study, the microbial barrier effectiveness of sterilization containers in the routine clinical setting can be tested with a quantitative microbial challenge test at intervals of 1 year to eliminate defect or ineffective containers as potential causal factors for nosocomial infections. An LRV of >4 should be envisaged as the target assurance level.