Microbiological surveillance after automated reprocessing of gastrointestinal endoscopes in routine clinical practice: A prospective randomized microbiological surveillance study

Microbiological surveillance is used to monitor the quality of gastrointestinal endoscope reprocessing, but prospective data comparing automated endoscope reprocessor systems under routine workflow conditions remain limited. We conducted an exploratory, single-center, prospective randomized surveillance study of 222 endoscope-use episodes involving patient-used forward-viewing upper and lower gastrointestinal endoscopes. Endoscope-use episodes were allocated 1:1:1 to strongly acidic electrolyzed water, ozonated water, or peracetic acid using an Excel-generated random-number procedure (n = 74 each). Assigned reprocessing was performed after standardized bedside pre-cleaning and manual cleaning. Post-reprocessing samples were obtained from predefined external and internal sites. Surveillance success was defined as ≤20 colony-forming units per sample at all sampled sites and absence of predefined indicator organisms. Success was achieved in 67/74 (90.5%) strongly acidic electrolyzed-water episodes, 71/74 (95.9%) ozonated-water episodes, and 71/74 (95.9%) peracetic-acid episodes. Risk differences in surveillance success versus peracetic acid were −5.4 percentage points (95% confidence interval, −14.6 to 3.2) and 0.0 percentage points (95% confidence interval, −7.7 to 7.7), respectively. In exploratory post hoc non-inferiority analyses using a −5 percentage-point margin, non-inferiority was not demonstrated for either functional-water system. A −10 percentage-point margin supported ozonated water but not strongly acidic electrolyzed water. Post hoc scope-level sensitivity analyses were directionally consistent with the primary analysis and highlighted the influence of repeated failures in an individual physical endoscope. These findings should be interpreted as exploratory microbiological quality-assurance data, not as evidence of clinical infection risk or comparative clinical effectiveness. Study registration: University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR), UMIN000061627 (registered May 19, 2026; enrollment began November 8, 2024).