The majority of organizations recommend microbial cultures for monitoring. The ESGE recommends that surveillance cultures be assessed at intervals of not more than 3 months. Moreover, the maximal total microbiological count should be <20 colony-forming units (cfu) for fluid collected after flushing the endoscope channels with 20 mL of sterile saline solution, with placement of 1 mL of the fluid on each agar plate.9 However, the accessibility to microbiology laboratories and the relative slow turnaround time make this method impractical,11 and standard culture methods cannot isolate viruses.4 Nevertheless, surveillance culturing to monitor endoscopes after reprocessing has been widely accepted because of its simple methodology and cost effectiveness, as well as the large number of accumulated studies supporting its use.121314

Bioburden assays detect proteins on the surface of endoscopes; protein and blood materials within the biopsy channel of endoscopes; and proteins, blood, and carbohydrates residing within the channel of endoscopes.911 These assays are easy to use and can produce rapid results. Furthermore, several commercial test kits are available, such as Scope-Check (Valisafe America, Tampa, FL, USA) and EndoCheck and ChannelCheck (Health Mark Industries, Fraser, MI, USA). Surface sampling with swabs, channel sampling with swabs, and sterile water flushing are conducted, and the swab or water sample is then mixed with the test reagent. It takes 10 to 90 seconds for results to be obtained. The proposed criteria for organic and bioburden residues remaining after proper manual cleaning and before HLD include <6.4 mg/cm² of protein, <1.2 mg/cm² of carbohydrate, and <2.2 mg/cm² of hemoglobin.15

Because ATP is present in microorganisms and cells, this test enables estimation of the contamination condition after reprocessing. The technique uses the light-producing reaction between ATP, luciferin, and luciferase to estimate the levels of ATP in a sample. The results can be obtained within a few minutes. Luminometers convert the number of photons released in the reaction into relative light units (RLUs). The proposed criterion is achieved when the bioluminescence reading is <200 RLUs.16 The sensitivity is 0.46 to 0.75 and the specificity is 0.43 to 0.81, compared with routine microbiological culturing. Although it does not seem appropriate to replace routine microbiological culturing with the ATP bioluminescence assay,17 ATP bioluminescence can provide a rapid and reliable measure of the effectiveness of the cleaning step prior to terminal disinfection.1819 The Centers for Disease Control and Prevention (CDC) protocol comments that non-culture methods such as ATP bioluminescence need systemic validation owing to a lack of consistent correlation to bacterial concentrations.20

PCRs have been used for detecting the human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and Helicobacter pylori. Even if the test result is positive; however, it does not necessarily mean a presence of infectivity.212223 As part of the new non-culture-based methods, measurement or quantitative PCR for monitoring needs to be further optimized because of its low specificity.24

The GESA recommends microbiological surveillance every 4 weeks on AERs and duodenoscopes and every 3 months on other GI endoscopes. The ESGE-ESGENA guideline committee recommends the intervals to be no longer than 3 months. The British Society of Gastroenterology (BSG) guidelines recommend annual surveillance testing.

Sampling from the channel of the endoscope can be performed in an anterograde or retrograde manner. Anterograde sampling refers to collection of the last-rinse water at the distal end of the endoscope. Retrograde sampling refers to collection of the water that is flushed from the distal end to the proximal end. Because retrograde sampling is considered more sensitive than anterograde sampling, the former is recommended for monitoring endoscopes after reprocessing.2426 Flushing or flush-brush-flush methods for sampling of the internal channel are introduced in some studies and guidelines.

Table 1 shows the sampling methods and sites and frequency of microbiological surveillance culturing set by different guidelines.

It is hard to test routinely for all species of bacteria, fungi, and viruses, so a culture target has to take into account the objective and cost. The BSG guidelines recommend annual testing for atypical mycobacteria in AERs. In the ESGE-ESGENA guidelines, Enterobacteriaceae, Pseudomonas aeruginosa, and staphylococci should be tested as indicator organisms, and atypical mycobacteria culture is recommended. The GESA-GENCA guidelines do not recommend routine testing for Legionella spp., anaerobes, H. pylori, and viruses. They recommend that bacterial cultures be directed to the detection of oral and enteric microorganisms such as coliforms (including Salmonella), enterococci, and viridans streptococci (but not anaerobes), as well as non-fermentative gram-negative bacilli (including Pseudomonas spp.). In samples from automated processors, non-fermentative gram-negative bacilli (including Pseudomonas spp.) and rapid-growing mycobacteria are the targets.

In the University Medical Center Groningen guidelines, bacterial isolates and yeasts are identified according to standard determination schemes.27

It is important to know how to interpret the culture results and what to do with the results. In the BSG guidelines, the presence of skin and environmental contaminants is not interpreted as a failure of disinfection. It simply means that endoscopes are not handled in a sterile fashion after decontamination. In the ESGE-ESGENA guidelines, growth of Enterobacteriaceae means insufficient cleaning and/or disinfection procedures, whereas growth of P. aeruginosa implies insufficient final rinsing and/or insufficient drying of endoscopes before storage. Growth of staphylococci results from endoscope recontamination. In the case of atypical mycobacteria (Legionella organisms) growth, contamination of the washer-disinfector and water system is suspected. For channels, the total microbiological count should be <20 cfu/channel; for water samples, it should be <10 cfu/100 mL. According to GESA-GENCA indications, growth of low numbers of skin microorganisms means contamination during the collection process rather than a significant problem with the disinfection or cleaning process, whereas growth of Pseudomonas spp. or other non-fermentative gram-negative bacilli is cause for serious and immediate concern and response. The repeated growth of significant numbers of enteric microorganisms from one instrument implies a mechanical defect in that instrument. Significant numbers of enteric microorganisms from a variety of instruments are most likely a result of inadequate reprocessing. The isolation of any Salmonella or Shigella species is a cause for concern.