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Nosocomial infections from contaminated endoscopes: a flawed automated endoscope washer. An investigation using
C J Alvarado1, S M Stolz, D G Maki
1Infection Control Department, University of Wisconsin Hospital and Clinics, Madison 53792.
Abstract:
Approximately 1 year after purchase of one manufacturer's automated endoscope washing machine, we began to detect heavy contamination of upper gastrointestinal (UGI) endoscopes cultured after cleaning and disinfection in the washer. During the first 6 months of 1988, 77% of surveillance cultures (20-mL flush through the biopsy channel) were positive for gram-negative bacilli (median concentration, 10(5) cfu/mL), most frequently Pseudomonas aeruginosa serotype 10. During the first 19 months of use of the washer, nosocomial post-UGI endoscopy colonization or infections with P. aeruginosa increased 36%. Investigations show that endoscope contamination derives from a flaw in the design of the EW-10 washer: the detergent holding tank, inlet water hose, and air vents cannot be reliably disinfected and contain heavy biofilms that recontaminate the machine after it has been disinfected, as specified by the manufacturer, with glutaraldehyde. Only by rinsing machine-cleansed endoscopes with 70% alcohol followed by forced air drying has reliable disinfection been achieved. Since adaptation of terminal alcohol treatment and drying, post-UGI endoscopy colonization or infection by P. aeruginosa has declined threefold (p less than 0.001). Testing in other centers using the manufacturer's EW-10 or EW-20 washer has shown similar contamination. In three centers, including our own, postendoscopy infections by machine-associated type 10 P. aeruginosa have been confirmed by demonstrating concordance between isolates from contaminated machines or endoscopes and from infected patients by immunoblot of whole cell lysates and by pulsed-field electrophoresis of DraI endonuclease-digested genomic DNA. This problem reaffirms the vulnerability to microbial contamination of water-containing apparatus and equipment in patient care and points up the critical importance of engineering design to prevent contamination.
Insights
Automated endoscope reprocessors can harbor Pseudomonas aeruginosa due to design flaws, leading to patient infections. Terminal alcohol rinsing and drying effectively eliminated contamination and reduced infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Medical Device Engineering
Background:
- Automated endoscope reprocessors (AERs) are crucial for preventing endoscope-associated infections.
- Design flaws in some AERs can lead to persistent microbial contamination.
- Pseudomonas aeruginosa is a common opportunistic pathogen associated with healthcare-associated infections.
Purpose of the Study:
- To investigate the cause of heavy gram-negative bacilli contamination in upper gastrointestinal (UGI) endoscopes processed by a specific automated endoscope washer.
- To determine the impact of this contamination on nosocomial infections.
- To identify effective methods for eradicating contamination and preventing post-endoscopy infections.
Main Methods:
- Surveillance cultures of UGI endoscopes after automated washing and disinfection.
- Microbiological analysis to identify bacterial species and serotypes.
- Investigation of AER design features contributing to contamination.
- Molecular typing (immunoblot and pulsed-field electrophoresis) to confirm patient-to-machine transmission.
- Clinical data analysis of nosocomial infection rates before and after intervention.
Main Results:
- 77% of endoscope cultures were positive for gram-negative bacilli, predominantly Pseudomonas aeruginosa serotype 10.
- Nosocomial P. aeruginosa infections post-UGI endoscopy increased by 36% during the study period.
- Design flaws in the AER (detergent tank, water hose, air vents) prevented complete disinfection and promoted biofilm formation.
- Terminal rinsing with 70% alcohol and forced air drying eliminated contamination.
- Post-intervention, P. aeruginosa infections declined threefold (p < 0.001).
Conclusions:
- The EW-10 automated endoscope washer's design is susceptible to microbial contamination, particularly P. aeruginosa.
- Biofilm formation in non-disinfectable components leads to recontamination of endoscopes.
- Terminal alcohol treatment and drying are critical for achieving reliable disinfection of endoscopes processed by this AER.
- Engineering design is paramount in preventing microbial contamination in patient care equipment.