Wastewater drain–associated CRO outbreaks

All 23 WWD-associated outbreaks were attributed to 1 or more CROs and occurred in acute-care hospitals. While a recent study has documented pathogenic yeast sink drain colonization and contamination of surrounding surfaces,Reference Jencson, Cadnum, Piedrahita and Donskey ³³ no WWD-associated outbreaks have been attributed to yeasts, fungi, or gram-positive organisms. Essentially, all outbreaks that fit the inclusion criteria for this report occurred in hospital areas where substantial populations of immunologically compromised patients were cared for, and these outbreaks were attributed to many different species of CRO. Only 1 rapidly contained outbreak, related to a single colonized sink, occurred on a general medical ward.Reference Mahida, Clarke, White, Vaughan and Bowell ²² As would be expected from the known global distribution of CROs, outbreaks associated with pathogens exhibiting metallo-β-lactamase genes were reported in Europe (n=6) and Australia (n=1) but not North America. While the level of sink colonization with ObS organisms ranged widely (16%–100%), the majority of implicated WWDs (61%) were ObS positive, and 5 of the sites that cultured >1 sink found all WWDs colonized with ObS pathogens.Reference Kotsanas, Cheong and Korman ^{13 ,} Reference Wolf, Bergervoet, Sebens, van den Oever, Savelkoul and van der Zwet ^{14 ,} Reference Davis, Jensen and Van Hal ^{17 ,} Reference Stjarne Aspelund, Sjostrom, Liljequist, Morgelin, Melander and Pahlman ^{19 ,} Reference DeGeyter, Blommaert and Verbraeken ²³ The review analysis revealed a very wide range in the duration of outbreaks (1–91 months), with 61% outbreaks lasting 2 or more years. Generally, the shorter outbreaks reflected a combination of rapid recognition of WWD ObS colonization and a limited period of follow-up after implementing initial mitigation interventions. While it is possible that they were incompletely characterized, some of the longer-duration outbreaks appeared to reflect relatively late identification of a WWD source of the outbreakReference Lowe, Willey and O’Shaughnessy ⁸ and/or partial use of retrospective data collation.Reference Breathnach, Cubbon, Karunaharan and Pope ^{11 ,} Reference Amoureux, Riedweg and Chapuis ²¹ Although not specifically described, it is likely that the very low incidence density of clinical cases, the typically long interval between cases, and the 68% of months without documented ObS infection or colonization both adversely impacted the recognition of an ongoing outbreak and confounded the assessment of possible responses to initial as well as subsequent mitigation interventions. Attributable mortality ranged widely from 0 to 50%, but it clustered near the mean of 33% in 6 of the 9 studies reporting this outcome.

Initial interventions reflected a wide range of traditional infection prevention activities that were specifically enhanced once an outbreak was suspected and prior to identification of WWDs having an ongoing role in the outbreak. Once WWD ObS colonization was identified, all sites implemented a wide range of liquid disinfection protocols while continuing enhanced infection prevention activities. Daily bleach protocols as part of initial mitigation activities were specifically identified as being ineffective in 9 reports.Reference Hota, Hirji and Stockton ^{4 ,} Reference La Forgia, Franke, Hacek, Thompson, Robicsek and Peterson ^{5 ,} Reference Lowe, Willey and O’Shaughnessy ^{8 ,} Reference Leung, Gray, YL Cheong, Haertsch and Gottlieb ^{9 ,} Reference Kotsanas, Cheong and Korman ^{13 ,} Reference Mahida, Clarke, White, Vaughan and Bowell ²² While Lowe et al noted that increasing a daily bleach protocol to thrice daily decreased ObS-positive drain cultures from 16.4% of sinks to 4.9%, an interruption in protocol compliance resulted in the sink colonization rate returning to 16.4%.Reference Lowe, Willey and O’Shaughnessy ⁸ Other WWD disinfection protocols found to be ineffective included a “phenolic disinfectant,”Reference Leung, Gray, YL Cheong, Haertsch and Gottlieb ⁹ an acetic acid protocol,Reference Stjarne Aspelund, Sjostrom, Liljequist, Morgelin, Melander and Pahlman ¹⁹ a glucoprotamin protocol,Reference DeGeyter, Blommaert and Verbraeken ²³ and the addition of a vaporized hydrogen peroxide system protocol to other interventions.Reference Paopradit, Srinitiwarawong, Ingviya, Singkhamanan and Vuddhakul ³²

Concomitantly or more usually in the setting of the limited effectiveness of enhanced infection prevention interventions and disinfectant-based protocols, many sites initiated WWD replacement activities. Although the removal of a single implicated sink was done in 2 studies, ongoing WWD colonization led to a more complex bleach protocol being implemented at 1 site, which was incompletely effective,Reference La Forgia, Franke, Hacek, Thompson, Robicsek and Peterson ⁵ and additional sink system replacements at the other site, which was incompletely evaluated.Reference Vergara-Lopez, Dominguez, Conejo, Pascual and Rodriguez-Bano ¹⁰ Replacement of multiple sinks was planned but not evaluated in 1 report.Reference Tokatlidou, Tsivitanidou, Pournaras and Ikonomidis ²⁶ Although all sinks were replaced as an initial intervention in the recent report by Gbaguidi-Haore et al,Reference Gbaguidi-Haore, Varin, Cholley, Thouverez, Hocquet and Bertrand ²⁴ colonization of the P-trap systems persisted. As a result, twice weekly bleach treatments of all sinks and P-trap replacement for sinks were associated with patient stays of >7 days. While no new clinical cases were identified during 36 months of follow-up, ObS WWD colonization continued to be documented.Reference Gbaguidi-Haore, Varin, Cholley, Thouverez, Hocquet and Bertrand ²⁴ Unfortunately, none of the 9 sites that initiated multiple sink system replacements described the direct objective evaluation of the impact of the intervention on WWD colonization over time.Reference Starlander and Melhus ^{7 ,} Reference Lowe, Willey and O’Shaughnessy ^{8 ,} Reference Vergara-Lopez, Dominguez, Conejo, Pascual and Rodriguez-Bano ^{10 ,} Reference Tofteland, Naseer, Lislevand, Sundsfjord and Samuelsen ^{12 ,} Reference Leitner, Zarfel and Luxner ^{16 ,} Reference Amoureux, Riedweg and Chapuis ^{21 –} Reference DeGeyter, Blommaert and Verbraeken ²³ An additional report noted that “no new cases were documented following sink system replacement,” but the duration of follow-up was not described.Reference Tofteland, Naseer, Lislevand, Sundsfjord and Samuelsen ¹² Five reports specifically noted the ineffectiveness or incomplete effectiveness of WWD system replacement.Reference La Forgia, Franke, Hacek, Thompson, Robicsek and Peterson ^{5 ,} Reference Kotsanas, Cheong and Korman ^{13 ,} Reference Wendel, Kolbe-Busch, Ressina, Schulze-Robbecke and Kindgen-Milles ^{15 ,} Reference Stjarne Aspelund, Sjostrom, Liljequist, Morgelin, Melander and Pahlman ^{19 ,} Reference Gbaguidi-Haore, Varin, Cholley, Thouverez, Hocquet and Bertrand ²⁴

The primary limitation of this analysis of WWD-associated outbreaks relates to variations in the degree to which the epidemiology and mitigation interventions were evaluated and/or described. Despite this limitation, the similarities between the reports, particularly related to the finding of high frequencies of WWD ObS colonization (mean, 60%), the very low incidence density of cases (<1 per month), the typically long interval between cases with 68% of months having no identified cases, as well as the documentation of multilevel mitigation failures are notable and highly consistent in these reports.

The epidemiology, but not the mitigation interventions, was described in 9 additional reports since 2000.Reference Kac, Podglajen, Vaupre, Colardelle, Buu-Hof and Gutmann ^{25 –} Reference Paopradit, Srinitiwarawong, Ingviya, Singkhamanan and Vuddhakul ³² All of these 9 studies were associated with CROs in ICUs, and 66% of the hospitals were located in Europe. Taken together, these 9 reports support the epidemiologic aspects of the 23 studies reviewed overall.

An additional limitation of this analysis is the fact that only 26% of studies utilized cultures to evaluate subsequent interventions on ObS contamination of the implicated WWDs. Despite this limitation, the well-documented failure of multiple interventions, including drain system replacement, is consistent with our evolving understanding of the epidemiology of the WWD-biofilm–associated microbiome.Reference Khariman, Weingarten and Conlan ^{34 ,} Reference Kotay, Chai, Guilford, Barry and Mathers ³⁵ Notably, the wastewater system laboratory work described by Kotay et alReference Kotay, Chai, Guilford, Barry and Mathers ³⁵ defined the resilience of horizontal drain system biofilm colonization and its ability to continuously support CRO-infected sink drain systems as a result of rapid regrowth of drain biofilm following mechanical biofilm removal. In this context, in the 9 reports discussed above, sink replacement failed to successfully mitigate ongoing WWD ObS colonization and/or transmission.Reference La Forgia, Franke, Hacek, Thompson, Robicsek and Peterson ^{5 ,} Reference Leung, Gray, YL Cheong, Haertsch and Gottlieb ^{9 ,} Reference Vergara-Lopez, Dominguez, Conejo, Pascual and Rodriguez-Bano ^{10 ,} Reference Tofteland, Naseer, Lislevand, Sundsfjord and Samuelsen ^{12 –} Reference Wendel, Kolbe-Busch, Ressina, Schulze-Robbecke and Kindgen-Milles ^{15 ,} Reference Chapuis, Amoureux and Bador ^{18 ,} Reference Stjarne Aspelund, Sjostrom, Liljequist, Morgelin, Melander and Pahlman ¹⁹

These reports were also limited by an inability to quantify rates of actual patient acquisition because none of the study sites utilized or reported CRO screening to define a direct relationship between individual WWD cultures and clinical cultures. While it is likely that many of the colonized WWDs did not continually transmit ObS organisms to patients directly, or more likely, indirectly,Reference Grabowski, Kang, Wells, Sifri, Mathers and Lobo ³⁶ the consistent and substantial maximal interval between ObS clinical cases (mean, 10.2 months) provides strong support for there being an ongoing causal relationship between contaminated WWDs and ongoing patient acquisition of CROs. In addition, the nature of these reports and their potential for selection bias limits the direct use of these studies to estimate how frequently WWD-associated outbreaks are occurring in acute-care hospitals. While it is possible that publication bias could overestimate the true incidence of outbreaks, Roux et alReference Roux, Aubier, Cochard, Quentin and van der Mee-Marquet ³⁷ documented widespread endemic CRO WWD colonization in 2013. In the only multisite evaluation of ICU WWD CRO colonization published to date, they confirmed CRO contamination in 89 sinks in the ICUs of 9 hospitals in France despite the fact that all sites were using various liquid-disinfectant protocols to suppress pathogen colonization.Reference Roux, Aubier, Cochard, Quentin and van der Mee-Marquet ³⁷ Despite ongoing mitigation activities, colonization with CROs, primarily K. pneumoniae and Enterobacter cloacae, was found in 0 to 81% of sink drains tested (mean, 31%).Reference Roux, Aubier, Cochard, Quentin and van der Mee-Marquet ³⁷ While additional studies of this type are needed, the findings of Roux et al support the possibility that WWD CRO-related outbreaks are more frequent than is currently recognized, particularly in high-risk patient settings. An additional factor that may be leading to the underrecognition of WWD CRO transmission is the high level of clonality of carbapenem-resistant K. pneumonia in North America, where 70% have similar antibiograms belonging to sequence type 258.Reference Chen, Anderson and Paterson ³⁸ Indeed, in the United States, the only recognized outbreak of environmentally transmitted KPC was initially recognized because of the uncommon finding of clostin resistance, which led to the recognition of additional cases over the ensuing weeks on the same hematology oncology unit.Reference Snitkin, Zelazny and Thomas ⁶

Drain-associated biofilm and the genetic transfer of resistance

Almost a decade ago, as genomic epidemiology became widely available, clusters of gram-negative healthcare-associated infections were found to have shared resistance plasmids not explained by patient-to-patient transmission,Reference Moquet, Bouchiat and Kinana ³⁹ which led to further studies of WWD biofilms.Reference Khan, Dancer and Humphreys ^{40 –} Reference Kizny Gordon, Mathers, Cheong, Gottlieb, Kotay and Walker ⁴⁴ It is now recognized that both vertical sink and shower drains as well as horizontal drain system pipes contain complex biofilm-associated microbiomes often contain CROs as well as a wide range of environmental commensal organisms.Reference Khan, Dancer and Humphreys ^{40 –} Reference Kizny Gordon, Mathers, Cheong, Gottlieb, Kotay and Walker ⁴⁴ Research has now confirmed the occurrence of plasmid-based intra- and interspecies carbapenamase exchange between WWD biofilm-associated pathogens. In 2008, Tokatlidou et alReference Tokatlidou, Tsivitanidou, Pournaras and Ikonomidis ²⁶ documented the clonal spread of a novel bla(VIM-12) metallo-β-lactamase gene among K. pneumoniae.Reference Tokatlidou, Tsivitanidou, Pournaras and Ikonomidis ²⁶ In 2013, Tofteland et alReference Tofteland, Naseer, Lislevand, Sundsfjord and Samuelsen ¹² confirmed the interspecies spread of a bla _KPC-2 plasmid in WWD-outbreak–associated pathogens. More recently, Wendel et alReference Wendel, Ressina, Kolbe-Busch, Pfeffer and MacKenzie ⁴⁵ found that biofilm-associated Enterobactericiae and nonfermenters shared metallo-β-lactamase GIM-1 plasmids. Subsequently, Michalikova et alReference Michalikova, Brnova, Hnilicova, Streharova, Liskova and Krcmery ⁴⁶ quantified transferrable antibiotic resistance in 39.4% of 137 randomly selected environmental Pseudomonas spp, Enterobacter spp, and Klebsiella ssp, finding that the most frequent plasma-mediated antibiotic resistance was present in E. coli (89%) followed by Pseudomonas spp (41%). In studies by Khariman et al,Reference Khariman, Weingarten and Conlan ³⁴ multiple variables were evaluated that impacted the horizontal transfer of carbapenamase plasmids; plasmid content, temperature, substrate as well as strain variables substantially impacted such transmission. Most recently, Stoesser et alReference Stoesser, Sheppard, Eyre, Dudley, Sebra and Peto ⁴⁷ found that 14 of 15 ICU room WWDs (93%) contained multiple CRO species that showed bla KPCs. Although transmission of CROs from WWDs represents only 1 of several hospital water-system reservoirs from which pathogens are disseminated,Reference Khan, Dancer and Humphreys ^{40 –} Reference Wendel, Ressina, Kolbe-Busch, Pfeffer and MacKenzie ⁴⁵ studies over the past 8 years have begun to clarify the bioepidemiology of these critically important components of patient-care WWD environments.

As summarized in Figure 1, our rapidly evolving understanding of the role of patient-zone WWDs in CRO transmission clarifies the urgent need for further research to qualify and quantify the role of wet biofilm in healthcare environments with respect to both the epidemiology of CROs as well as other Enterobacteriaceae, yeasts, and possibly fungi in a range of healthcare settings. Given the finding that multiple, apparently initially successful, WWD mitigation interventions were later found to be substantially or completely unsuccessful (often after a delay of many months), an assessment of the effectiveness of interventions to mitigate drain biofilm-associated pathogen contamination and transmission might initially be best evaluated by mock-up sink laboratory investigations such as those described by Kotay et al.Reference Kotay, Chai, Guilford, Barry and Mathers ³⁵ Additionally, the likely role of healthcare worker hands in the transmission of WWD CROsReference Grabowski, Kang, Wells, Sifri, Mathers and Lobo ³⁶ and the documentation that bla-KPC–carrying K. pneumonia was cultivable on plastic and steel for up to 5–6 days, and thereafter viable but noncultivable,Reference Strich and Palmore ⁴⁸ support the need for studies to clarify the role of intermediate fomites in CRO outbreaks. However, the potential role of WWD colonization in CRO outbreaks is not widely recognized. A review published in May 2017 providing detailed recommendations for interventions to optimize recognition and control of CRO stated, “Carbapenem-resistant Enterobactericae have been found infrequently in the environment of infected or colonized patients,”Reference Friedman, Carmeli, Walton and Schwaber ^{49 (p.586)} but these researchers failed to consider the possible role of WWDs in CRO acquisition. Although none of the 6 CRO outbreaks reported in 2017 investigated WWDs as a possible source for ongoing patient acquisition,Reference Munier, Biard, Rousseau, Legrand, Lafaurie and Lomomt ^{50 –} Reference Robustillo-Rodela, Perez-Blanco, Ruiz and Ruiz Carrascoso ⁵⁶ greater awareness of the potential for WWDs to perpetuate CRO dissemination may lead to the routine evaluation of these sites in all CRO outbreak investigations in the future.

Fig. 1 Summary of wastewater drain carbapenem-resistant organism outbreak characteristics.

Clearly, further studies are needed to clarify and quantify the dynamics of WWD biofilm plasmid exchange because it is now clear that, as Wendel noted, “Drains may serve as a melting pot for horizontal gene transfer, for dissemination into new species, and as a reservoir to propagate future hospital outbreaks.”Reference Wendel, Ressina, Kolbe-Busch, Pfeffer and MacKenzie ^{45 (p.3605)} While developing effective interventions to prevent transmission of WWD pathogens to patients is of immediate importance, it will be equally critical to concomitantly evaluate and mitigate WWD biofilm-colonizing plasmid-mediated antimicrobial resistance.