Endoscope contamination and rinse water TVCs

Pamela Ashman, Paul Hay, Emma Lindsay, Fara Shadroo, Joanna Ford and Pete Phillips

October 6th 2015


The link between contaminated endoscopes and outbreaks of infection (both genuine outbreaks of infection and pseudo-outbreaks where positive samples are taken from patients not exhibiting clinical symptoms of infection) has long been established (Srinivasan et al., 2003 and Wang et al., 1995). Failure of procedures can cause contamination (Moses and Lee 2004) and monitoring bacterial levels in rinse water can be a useful indicator of system or technique failures (Leung et al., 2003). The Choice Framework for local policy and procedure (CFPP  01-06) and the equivalent policy in Wales (WHTM 01-06) states that less than 10 colony forming units (or CFUs) of bacteria detected in 100ml of rinse water is considered acceptable. This figure is frequently referred to as the TVC (total viable count). 

However, the relationship between rinse water CFU levels and endoscope contamination is still unclear - does a high level of rinse water CFUs  correlate with contamination of the endoscope itself? 


The flushing of endoscopes with sterile liquid which is then cultured to identify any residual bacteria is a potentially useful tool. Studies have shown that consistently positive cultures from the same instrument can readily identify faulty instruments or failures in cleaning procedure (Moses et al., 2003, Chiu et al., 2010). One five year study cultured flushes from 'disinfected' endoscopes and swabs from the inside of AERs that were used to reprocess them (Chiu et al., 2012). Significantly more positive cultures were obtained from the instrument flushes compared with the corresponding AER swabs. The authors concluded that culturing flushed liquid from endoscopes was a superior method of detecting instrument contamination. If high levels of CFUs are found in the rinse water, users may be cautious about using the endoscope clinically.   Flushing the scope with sterile water and analysing the samples may be of real benefit in establishing whether the endoscope is itself contaminated.

SMTL were asked to analyse some water samples from two endoscope departments in Wales for an extended period. The departments wanted additional data so that they could examine their decontamination and storage processes in more detail. The rinse water samples were taken from the washer disinfector (WD). The (used) endoscopes were then reprocessed, and following reprocessing, the internal channel/s of the endoscopes were flushed with sterile water which was collected for analysis.  Samples were then transported to the laboratory where they were were filtered through a fine filter membrane. which was then placed on agar plates and incubated for up to 5 days.  Following this, colony forming units were counted on the plate and the results were expressed as the number of CFUs per 100 mls.    

The following graphs show the approximate number of CFUs (per 100 ml sample) from one endoscope WD  and endoscopes that have undergone a full reprocessing cycle within that specific machine. The top graph (Before Machine) shows the levels of TVC sampled from the mains water before it entered the machine, the middle graph (Inside Machine) shows levels from samples taken from within the WD machine following reprocessing and the bottom graph (Scope) shows levels found when reprocessed endoscopes were flushed with sterile water and the samples incubated. Results were taken over the course of one year.

Results and discussion

Visual assessment of the graphs reveals no clear correlation (or lagged correlation) in results between the CFU concentration flushed from the endoscope and the CFU concentrations in rinse water samples from the Washer Disinfector. The patterns of peaks on the graphs are completely different between the instrument flush and the rinse water results. As the rinse water is the last liquid to flush through the endoscope, intuitively one may expect the CFU levels in the instrument to reflect the rinse water pattern, but that is not borne out by these results. 

During general monitoring of the reprocessing system, it is the sudden and unusual changes in CFU levels (shown as peaks on the graphs) that usually alert the user to possible problems with the process. It could be, for example, that the peaks in CFU levels in rinse water indicate a reprocessing failure, whilst the peaks in instrument levels indicate a fault within the instrument itself (such as a defect in the channel which is not being cleaned effectively and is harbouring bacteria). This may explain the different patterns in CFU concentration seen in the graph.

Current standards exclusively use the characteristics of rinse water (including CFU levels) to monitor the system. However, in terms of patient health,  assessing the bioburden of the instrument itself would seem more relevant. The results indicate that monitoring both the instrument and the rinse water may be the best course of action, giving data on the process control (the WD water) and on the patient contact device itself.  

The testing on which this article is based was undertaken for two endoscope departments as additional information for operational purposes, and was not designed as a research experiment. If the work were to be repeated, we would want to control some of these measures, including:

  • the type of endoscopes used - instruments would preferably need to be standardised (a variety were assessed in the data presented here)
  • the method of bioburden retrieval - for example, whether flushing or brushing the endoscopes produces the most useful and standardised result
  • neutralisation of sample at the point of collection - any residual paracetic acid in the samples (from the disinfection process) must be neutralised to prevent bactericidal activity in samples following collection. Samples used for this report were collected in pots containing 20mg/L thiosulphate (the standard concentration of neutralising agent for water sampling bottles). If total neutralisation does not take place, some bacteria may be killed following sample collection, which would lead to inaccurate (i.e. lower) CFU counts. Validation would need to be performed to ensure that complete neutralisation has been achieved.

In conclusion, the data from this project provides useful information on the relationship between rinse water and endoscope contamination, and identifies additional testing (rinse channel testing) which, if undertaken, may provide extra data which can be used to make patient-safety related decisions about Washer Disinfectors, rinse water, and endoscope contamination. 


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Wang H-C, Liaw Y-S, Yang P-C. A pseudoepidemic of Mycobacterium chelonae infection caused by contamination of a fibreoptic bronchoscope suction channel. European Respiratory Journal. 1995;8:1259-1262

Welsh Health Technical Memorandum (WHTM 01-06) 2014. Decontamination of flexible endoscopes part D. Testing Methods. Shared Service Partnership, Specialist Estates Services.


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