Evaluation of pyrogens remaining on reusable medical devices after washing and sterilization

In this study, we determined the most appropriate method to evaluate the amount of pyrogens, including bacterial endotoxins, remaining on reusable medical devices after washing and sterilization, and investigated an improved sterilization method to reduce the contamination level of pyrogens. Scissors used for surgery were provided from six hospitals after cleaning with a washer disinfector, and then sterilized with an autoclave or low-temperature ozone/hydrogen peroxide (O3/H2O2) mixed gas exposure. The amount of pyrogens remaining on the scissors was evaluated through direct human cell-based pyrogen tests (HCPTs) and Limulus amebocyte lysate (LAL) coagulation assays. A direct HCPT revealed that an average of 0.977-20.7 EU/device of pyrogens remained on the autoclaved scissors, and this amount decreased to 0.177-5.16 EU/device after the sterilization with O3/H2O2 mixed gas. Conversely, with the LAL assay, no endotoxins were detected in two samples and only 0.0107-0.894 EU/device of endotoxins were detected on other sample sets, regardless of the type of sterilization method used. These results suggest that O3/H2O2 mixed gas sterilization is very effective in reducing the contamination level of pyrogens remaining on reusable medical devices and that the HCPT is more accurate than the LAL assay by which false negative or low quantitative results were obtained in the evaluation of residual endotoxins.