Five-year prospective microbiological evaluation of sterilised operating room supplies stored under event-related sterility maintenance conditions: a single-centre study with molecular characterisation of a fungal contaminant

BACKGROUND: Time-related sterility maintenance (TRSM) remains standard practice in many Japanese operating rooms (ORs), requiring routine re-sterilisation of unopened supplies at fixed intervals. International guidelines increasingly endorse event-related sterility maintenance (ERSM), yet long-term prospective data from clinical settings remain limited. AIM: To evaluate the 5-year sterility maintenance of OR supplies stored under ERSM-consistent conditions and to characterise any microbial contaminant detected. METHODS: Representative materials (titanium, cotton, and latex) were sterilised (steam, ethylene oxide, or vaporised hydrogen peroxide), double-pouched in ISO 11607-1-compliant systems, and stored in closed cabinets. One hundred and eight specimens were cultured at six time points (12, 18, 24, 36, 48, and 60 months) using the Japanese Pharmacopoeia (18th edition) sterility test, harmonised with United States Pharmacopeia (USP) and Ph. Eur. 2.6.1. Culture-positive isolates underwent Internal Transcribed Spacer (ITS) rDNA sequencing. FINDINGS: Of 108 specimens, 107 (99.1%) remained culture-negative after 14 days of incubation. One steam-sterilised instrument (at the 12-month point) yielded a single fungal colony identified as Parengyodontium sp. (closest relatives: P. torokii and P. album; BSL-1). No visible package breach was identified. All 90 specimens tested at subsequent time points (18-60 months) were culture-negative. CONCLUSION: OR supplies maintained high sterility for five years under ERSM. The single early-positive result, followed by 48 months of complete sterility, suggests an incidental handling event rather than time-dependent degradation. However, variabilities in storage, handling, and packaging across institutions may affect long-term sterility; any ERSM transition should be supported by institutional validation and routine monitoring.