Investigation of microbiological non-compliance of endoscopic final rinse water associated with opportunistic premise plumbing pathogens contamination in connecting tube

Non-compliant final rinse water (microbial culture results exceeding 10 cfu/100 mL) is an under-recognized risk factor for failure of flexible gastrointestinal (GI) endoscope reprocessing, since it is an important step following disinfection during the reprocessing of flexible endoscopes. Opportunistic premise plumbing pathogens (OPPPs) may colonize terminal segments of the water distribution system and compromise rinse water quality. This study investigated the cause of recurrent final rinse water non-compliance in a GI endoscopy unit and evaluated an engineering intervention to prevent it. During August 2024, samples were collected from 34 reprocessed flexible gastrointestinal endoscopes (102 post-reprocessing samples) and various points within the water delivery system, including purified water and final rinse water from automated endoscope reprocessors and manual washing tanks. All samples were subsequently cultured for microbial analysis. After contaminated connecting tubes were identified as a potential OPPPs reservoir, 10 tubes between the circulation loop and the reprocessing equipment were replaced, and surveillance cultures were repeated at the same sampling sites. Initial assessments revealed low compliance rates of 32 water samples (37.5%, 12/32), according to infection control standards (≤ 10 cfu/100 mL). Water samples collected before connecting tubes showed 100% compliance (12/12 samples). Water collected through connecting tubes and final rinse taps all showed 0% compliance (0/10 samples), except for the water sample from AER 6, which had a bacterial count of 75 cfu/100mL, all other samples contained too numerous bacteria and could not be counted. The dominant bacteria is Sphingomonas paucimobilis, which was found in 14 samples, with a composition ratio is 43.75% (14/32). Others are Methylobacterium oryzae (8/32, 25%), Chryseobacterium indologenes (6/32, 18.75%), and Herbaspirillum huttiense (2/32, 6.25%). After replacing the connecting tubes, the compliance rate of water samples developed significantly to 100% (32/32) (P = 6.9 × 10− 8). The primary reason for non-compliance of final rinse water is the contamination of connecting tube by the OPPPs. These findings emphasize the need for shortening the connecting tube length and thorough cleaning and disinfecting of connecting tube between circulating tube and endoscope reprocessor, which are generally neglected in routine maintenance.