although the risk of endoscopy - related transmission of infection is estimated to be very low , more health care - associated infections are related to contaminated endoscopes than to any other medical device . flexible endoscopes can get highly contaminated with microorganisms , secretions , and blood during use . the narrow lumens and multiple internal channels make the cleaning of flexible endoscopes a complex and difficult task . bacteria are able to form biofilms on the inner channel surfaces , which can contribute to failure in the reprocessing of endoscopes 1 . several federal agencies , such as the centers for disease control and prevention ( cdc ) , and professional organizations such as the american society for gastrointestinal endoscopy ( asge ) and the european society of gastrointestinal endoscopy ( esge ) , have developed endoscope reprocessing guidelines . most of the european recommendations are based on publications from the international organization of standardization , iso 15883 . in general , endoscope reprocessing includes pre - cleaning ( at bedside ) , leak testing , manual cleaning , high - level disinfection , rinsing , drying , and storage . an automated endoscope reprocessor ( aer ) could be used to perform leak testing , high - level disinfection , and to rinse the flexible endoscope . the us food and drug administration has approved only one aer that eliminates the manual cleaning step . still , manual cleaning before disinfection is necessary because flexible endoscopes can contain a high bio burden . because post - marketing clinical data on the efficacy of the cleaning phase of the aer are limited , manual cleaning lack of cleaning or failure during the cleaning process could lead to the survival of pathogens after disinfection , increasing the risk of cross - contamination between patients . in addition , bacteria that remain after insufficient reprocessing may form a biofilm inside the instruments . a problem or outbreak due to a flexible endoscope can be detected in two ways . the first is a deviation in data on infections gathered through active surveillance in the hospital . if the same endoscope was used on two patients who have become infected , the device will can be cultured to confirmation colonization . the second way to detect an outbreak is through surveillance of endoscopes and aers to ascertain bacterial growth , which should lead to screening of patients . when an endoscope , aer , or screened patients show growth of the same bacteria , typing should be performed to determine whether the cluster ( outbreak ) is due to a contaminated endoscope or aer . incidence of carbapenem - resistant enterobacteriaceae ( cre ) and other multidrug - resistant micro - organisms ( mdro ) are increasing worldwide , and with them , the threat to public health because of limited treatment options . given the linkage between contaminated flexible endoscopes and outbreaks of cre and other mdros , it is not surprising that they have been associated with higher patient morbidity and mortality 6 . despite the availability of international , national , and local endoscope reprocessing guidelines , contamination and transmission of microorganisms continue 7 . most such transmissions are related to use of defective equipment , endoscope reprocessing failures , and non - compliance with recommended guidelines 3 
 8 . this article presents an overview of publications on case reports and outbreaks related to contamination of flexible endoscopes . the following search terms or combinations of terms were used to search in pubmed : endoscope , endoscope reprocessing , outbreak and infection . the collected studies are divided into four categories : damaged or defective flexible endoscopes , failures during manual endoscope reprocessing , reprocessing failures where the disinfection step was carried out by an aer , and failure or malfunctioning of the aer . thirty - two publications were included in this review . of them , eight incidents involved damaged or defective flexible endoscopes , eight were related to failures during manual endoscope reprocessing , 11 reports related to reprocessing failures associated with disinfection carried out using an aer , and five reports documented failure or malfunctioning of the aer . eight publications were identified in which damaged bronchoscopes were involved in cross - contamination ( table  1 ) . damage ranged from deteriorated equipment ( e.  g. , a damaged internal channel ) to a loose biopsy - port cap . five incidents were due to contamination of the endoscope with pseudomonas aeruginosa , including three publications that reported contamination of damaged bronchoscopes with both pseudomonas aeruginosa and three other species ( serratia marcescens , pseudomonas putida , stenotrophomonas spp . ) contamination of an endoscope with mycobacterium tuberculosis also was described 15 , as was contamination of two endoscopes with klebsiella pneumoniae , proteus vulgaris , proteus mirabillis , and morganella morganii in another publication , and contamination of a bronchoscope with a cre k. pneumoniae in another report 17 . 
  abbreviation : cre ; carbapenem - resistant enterobacteriaceae  
 table  2 lists eight publications in which failures during endoscope reprocessing were reported . problems ranged from inadequate use of equipment to non - compliance with endoscope reprocessing guidelines . five out of eight publications described contamination with p. aeruginosa , including one publication that reported contamination with both p. aeruginosa and serratia marcescens 
 18 
 19 
 20 
 21 
 22 . one study described contamination with k. pneumoniae ( new delhi metallo - beta - lactamase ( ndm)-positive ) 
 23 . in two other studies , contamination with , trichosporon spp .  and abbreviations : aer ; automatic endoscope reprocessor ; ndm-1 ; new delhi - metallo - bta - lactamase 
 table  3 lists 11 publications in which failures during endoscope reprocessing were described that involved disinfection carried out with an aer . in four of the studies , contamination of endoscopes was with p. aeruginosa 
 28 
 29 
 30 
 31 . in three other studies , involving a duodenoscope , contaminated was with k. pneumoniae ( esbl- and cre - positive ) 24 
 25 
 32 . the other two publications involving a duodenoscope described contamination with escherichia coli ( ndm- and cre - positive ) and methylobacterium mesophillicum 
 14 
 33 . two studies listed in table  3 also described contamination with mycobacterium tuberculosis , mycobacterium chelonae , and methylbacterium mesophillicum 
 34 
 35 . abbreviations : aer ; automatic endoscope reprocessor ; esbl ; extended - spectrum beta - lactamase ; cre ; carbapenem - resistant enterobacteriaceae ; ndm-1 ; new delhi - metallo - bta - lactamase five publications that related problems with an aer are listed in table  4 . in three of the studies , endoscope contamination with burkholderia cepacia , pseudomonas aeruginosa , and mycobacterium chelonae , respectively , due to a problem with the aer were described 36 
 37 
 38 . two other publications reported malfunctioning aers that did not lead to transmission of microorganisms 39 
 40 . abbreviation : aer ; automatic endoscope reprocessor as shown in table 1 , 2 , 3 & 4 contaminated endoscopes cause infections and may have contributed to the death of some patients . the most common infections are bloodstream ( bacteraemia or sepsis ) , pneumonia and urinary tract infections . eight publications were identified in which damaged bronchoscopes were involved in cross - contamination ( table  1 ) . damage ranged from deteriorated equipment ( e.  g. , a damaged internal channel ) to a loose biopsy - port cap . five incidents were due to contamination of the endoscope with pseudomonas aeruginosa , including three publications that reported contamination of damaged bronchoscopes with both pseudomonas aeruginosa and three other species ( serratia marcescens , pseudomonas putida , stenotrophomonas spp . ) contamination of an endoscope with mycobacterium tuberculosis also was described 15 , as was contamination of two endoscopes with klebsiella pneumoniae , proteus vulgaris , proteus mirabillis , and morganella morganii in another publication , and contamination of a bronchoscope with a cre k. pneumoniae in another report 17 
 . table  2 lists eight publications in which failures during endoscope reprocessing were reported . problems ranged from inadequate use of equipment to non - compliance with endoscope reprocessing guidelines . five out of eight publications described contamination with p. aeruginosa , including one publication that reported contamination with both p. aeruginosa and serratia marcescens 
 18 
 19 
 20 
 21 
 22 . one study described contamination with k. pneumoniae ( new delhi metallo - beta - lactamase ( ndm)-positive ) 
 23 . in two other studies , contamination with , trichosporon spp .  and abbreviations : aer ; automatic endoscope reprocessor ; ndm-1 ; new delhi - metallo - bta - lactamase table  3 lists 11 publications in which failures during endoscope reprocessing were described that involved disinfection carried out with an aer . in four of the studies , contamination of endoscopes was with p. aeruginosa 
 28 
 29 
 30 
 31 . in three other studies , involving a duodenoscope , contaminated was with k. pneumoniae ( esbl- and cre - positive ) 24 
 25 
 32 . the other two publications involving a duodenoscope described contamination with escherichia coli ( ndm- and cre - positive ) and methylobacterium mesophillicum 
 14 
 33 . two studies listed in table  3 also described contamination with mycobacterium tuberculosis , mycobacterium chelonae , and methylbacterium mesophillicum 
 34 
 35 . abbreviations : aer ; automatic endoscope reprocessor ; esbl ; extended - spectrum beta - lactamase ; cre ; carbapenem - resistant enterobacteriaceae ; ndm-1 ; new delhi - metallo - bta - lactamase five publications that related problems with an aer are listed in table  4 . in three of the studies , endoscope contamination with burkholderia cepacia , pseudomonas aeruginosa , and mycobacterium chelonae , respectively , due to a problem with the aer were described 36 
 37 
 38 . two other publications reported malfunctioning aers that did not lead to transmission of microorganisms 39 
 40 . abbreviation : aer ; automatic endoscope reprocessor as shown in table 1 , 2 , 3 & 4 contaminated endoscopes cause infections and may have contributed to the death of some patients . the most common infections are bloodstream ( bacteraemia or sepsis ) , pneumonia and urinary tract infections . there is an assumption that the risk of cross - contamination is almost non - existent when flexible endoscopes are reprocessed in accordance with accepted guidelines 7 . nevertheless , studies have found that , despite adherence to cleaning and disinfection guidelines , endoscopes can remain contaminated , leading to infections 41 
 42 . defects , either during production or during use , such as a loose biopsy - port cap , can cause outbreaks or infections 11 
 12 
 13 . therefore , manufacturers recommend periodic maintenance to ensure that no defect occurs during the life cycle of a flexible endoscope . guidelines for reprocessing of flexible endoscopes are ineffective if not implemented and applied correctly 11 
 20 . several studies have shown that non - compliance with reprocessing guidelines may lead to endoscope - related health care - associated infections 7 
 8 
 43 . studies suggest that lack of education is one of the reasons that guidelines are not strictly followed . staff assigned to reprocess flexible endoscopes should receive device - specific reprocessing training to ensure that they follow procedures for proper cleaning and high - level disinfection or sterilization . in addition , competency testing of staff responsible for reprocessing of flexible endoscopes should be implemented and only staffed deemed competent should be allowed to perform this task 3 
 44 
 45 
 46 . the clean - trace adenosine triphospathe ( atp ) water test , which is performed on manually cleaned endoscopes , can be considered as an auditing tool 47 
 48 . it is a rapid and practical way to check the cleanliness of endoscopes immediately after they have been manually cleaned . the test measures atp levels , which are present in microorganisms and human cells ; levels up to 200 relative light units ( rlus ) are considered acceptable . as described in alfa et al 47 , the elevator guide - wire channel the problems with duodenoscopes documented in the literature identified in this review were often related to this channel ( table  2 and table  3 ) . therefore , incorporating an atp test into the auditing procedure would help detect and prevent cross - contamination of duodenoscopes . in addition , health care workers involved in reprocessing should be made aware of the patient safety issues that can arise from any oversights and inaccuracies in their work . aers improve standardization of the reprocessing steps , reduce personnel exposure to high - level disinfectants , infectious material and lower the possibility of human errors 2 . they reduce the amount of hands - on work and provide documentation of each cleaning cycle 43 . despite their obvious advantages , the use of aers is not specifically mentioned in various guidelines and recommendations 4 
 8 
 49 . in addition , failures of aers are reported and linked to infection outbreaks or colonization 2 . furthermore , the function of the water filtration system in aers might not be reliable in providing bacteria - free water 50 . in view of their advantages , as well as the fact that they can be a potential source of contamination , aers should be intergraded in endoscope reprocessing guidelines . there is no evidence available that manual disinfection of endoscopes increases the risk of microorganisms transmission compared to using an aer . however , manual reprocessing can not be standardized and validated , and are prone to human error .   as with the use of aer , not all guidelines recommend routine microbiological testing of flexible endoscopes and aers for quality assurance 2 
 51 . testing remains controversial in the absence of a standardized procedure for microbiological testing , frequency of testing , and interpretation of results . also problematic is the lack of a threshold beyond which colonization of an endoscope by different bacteria becomes problematic . in the absence of guidelines , health care facilities have created their own procedures for microbiological testing , thus potentiating the risk of inadequate testing . an outbreak already has been documented that is believed to be a result of contamination of flexible endoscopes due to inadequate testing procedures , which was overlooked 25 . standardized routine microbiological testing should be implemented based on existing guidelines , as has been done with german , dutch , and australian guidelines 52 
 53 
 54 . in addition , given the recent cre outbreaks , attention needs to be given to strict adherence to instructions for brushing the area around , near , and behind the forceps elevator , which is located at the distal end of the duodenoscope . that part is difficult to clean because of its design , which consists of a small tube that includes a small mobile metal piece called the elevator ( fig .  1 ) . manual step of brushing is needed to prevent possible transmissions of cre and of other multidrug - resistant organisms during flexible endoscopy . when confronted with an outbreak of cre due to contaminated flexible endoscopes , the use of ethylene oxide ( eto ) sterilization for reprocessing is worth considering 6 . because not all incidences are reported or published , the studies described here probably represent just a fraction of the total number of reprocessing failures . in a recent publication , dirlam langlay et al . 55 summarized reprocessing lapses that occurred but were not documented in the published literature over a 7-year period in north america . based on media reports and related sources , the authors found 27 lapses , whereas only one case was described in a peer - reviewed article .   despite the fact that colonoscopy is the gastrointestinal endoscopic examination most frequently performed worldwide , no outbreaks related to the procedure have been described in the peer - reviewed literature . a review by morris et al . the risk of patient - to - patient transmission of blood - borne viruses seems to be low , even with inadequate decontamination procedures . only one case of probable hepatitis b transmission and two cases of probable hepatitis c transmission were described . the lack of publications in peer - reviewed literature gives the false perception that reprocessing failure is a rare occurrence . mandatory reporting of lapses to a national registry would give a better overview of incidents and facilitate more in - depth investigations , leading to better guidelines . in conclusion , mandatory competency training and periodic auditing are necessary to ensure the quality of reprocessing of flexible endoscopes . early detection of contamination would be easier if standardized periodic microbiological testing were included in the guidelines . because aers are often used for flexible endoscope reprocessing , they should be included in the guidelines . periodic maintenance of flexible endoscopes and aers should always be carried out as the manufacturer advises . mandatory reporting of lapses would provide a broader perspective on the worldwide incidence of cross - contamination of flexible endoscopes .
flexible endoscopes are widely used to examine , diagnose , and treat medical disorders . 
 while the risk of endoscopy - related transmission of infection is estimated to be very low , more health care - associated infections are related to contaminated endoscopes than to any other medical device . 
 flexible endoscopes can get highly contaminated with microorganisms , secretions and blood during use . 
 the narrow lumens and multiple internal channels make the cleaning of flexible endoscopes a complex and difficult task.despite the availability of international , national and local endoscope reprocessing guidelines , contamination and transmission of microorganisms continue to occur . 
 these transmissions are mostly related to the use of defective equipment , endoscope reprocessing failures , and noncompliance with recommended guidelines . 
 this article presents an overview of publications about case reports and outbreaks related to contamination of flexible endoscopes .