Endoscope disinfection and its pitfalls - requirement for retrograde surveillance cultures

Background and study aims: Several endoscopy-related outbreaks of infection have been reported in recent years. For early recognition of inadequate disinfection of endoscopes we designed a microbiological surveillance system to evaluate the efficacy of the cleaning and disinfection procedure, and to trace disinfection problems to individual endoscopes or washer-disinfectors. Methods: Our surveillance protocol included anterograde and retrograde sampling, a decision algorithm, genetic fingerprinting, and scanning electron microscopy. Results: Over a period of 29 months we found an increasing number of patient-ready endoscopes testing positive for Candida species other than albicans, especially C. parapsilosis. These yeasts were also isolated from the washer-disinfectors. The number of positive tests for Candida species varied from 1 out of 21 to 14 out of 27 samples from nine frequently used endoscopes. The number of colony-forming units per milliliter ranged from 1-10 to 3000 for endoscopes and 0.002 to 0.06 for the washer disinfectors. DNA fingerprinting was not able to discriminate different strains within C. parapsilosis. Conclusions: Our protocol was able to detect a structural problem in the endoscope disinfection process. Retrograde sampling was crucial for this purpose, because it has much higher sensitivity than anterograde sampling. Endoscopes with damaged working channels are probably the source of the contamination problem with Candida species