Infection Control & Hospital Epidemiology


cultures were not included.) In the studies reviewed, the actual number of clinical cases identified per month was typically quite low (n=1–10; median <1). Indeed, no clinical cases were identified during 578 of the 850 months evaluated (68%). The longest interval between cases ranged from 1 to 40 months (mean, 10.2 months) in the 17 studies from which such information could be obtained (Table 1). The attributable mortality rate reported in 9 studies ranged from 0 to 50% (mean, 33%).


Interventions to mitigate outbreaks


The duration of the outbreaks before implementation of initial mitigation activities directed at WWDs was often substantial in the 21 studies that allowed for such a determination (Table 1). While the interval was only 1 month in 3 studies,11,20,22 it was between 6 and 12 months in 7 studies4–8,16,17 (mean, 8.8 months) and between 24 and 84 months in an additional 7 studies (mean, 53 months).9–11,15,19,21,24 Once an outbreak was recognized, 19 sites implemented multiple enhanced infection prevention interventions such as increased hand hygiene edu- cation, hand hygiene monitoring, reinforced contact precau- tions, cohorting infected and colonized patients, cohorting staff caring for such patients, and increased emphasis on daily as well as terminal cleaning practices. Also, 10 sites initiated screening protocols and isolation of asymptomatic ObS gastrointestinal carriers. Although some reports may have included cases identified retrospectively, 2 studies were primarily retrospective, implementing interventions only after an ObS was cultured from 1 or more WWDs.11,21 All sites utilized a wide range of focused WWD mitigation interventions with or without the enhanced infection prevention interventions following recognition ofWWDcolonization by ObS organisms (Table 1). Such initial interventions included liquid disinfectant–based protocols using bleach,9,13,22 acetic acid pro- tocols,9,19 “double-strength phenolic disinfection,”9 a glucoprota- min disinfection protocol,23 the use of a “steam plunger tool,”13 and a hydrogen peroxide vapor protocol.23 Furthermore, 5 studies described environmental structural interventions as part of the initial outbreak control activities, including single sink replace- ment5,10,12 and multiple sink system replacements.19,24 All 21 sites with outbreaks that were studied for >1month documented ongoing patient infection or colonization with the ObS organism(s) and/or persistent WWD colonization with the ObS pathogen(s) despite initial remediation activities. In 7 sites, the failure of these interventions led to subsequent interventions including a bleach-basedWWD system flooding protocol,5,9,18,24 multiple environmental interventions,6 a thrice daily bleach treatment protocol,18 “biofilm removal,” and a daily bleach treatment protocol (Table 1).19 While not quantified, 7 studies noted that the design of sinks and sink areas might have had a role in outbreak perpetuation.9,11,13,15,16,24 Also, 14 sites described WWD system replacement, usually of multiple sinks,3,4,6–8,13–16,20–24 as part of subsequent interventions. Overall, 16 of 21 reports (76%) did not describe culture-based WWD evaluation of the effectiveness of these apparently final interventions.3,4,6–8,10,11,13,14,16,17,20–23 Although 3 reports described a partial response to interventions,13,18,24 6studies described objectively confirmed failure of final mitigation activities.5,9,11,15,19,24 Of the studies evaluating a response to mitigation activities, only 4 sites used culture-based assessment of the effectiveness of sink system replacement, and all 4


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confirmed ongoing or recurrent WWD colonization with ObS organisms.5,13,15,24


Discussion 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,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.22 As would be expected from the known global distribution of CROs, outbreaks associated with pathogens exhibiting metallo-β-lacta- mase 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.13,14,17,19,23 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 out- breaks reflected a combination of rapid recognition ofWWDObS 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 out- breaks appeared to reflect relatively late identification of a WWD source of the outbreak8 and/or partial use of retrospective data collation.11,21 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 docu- mented 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. OnceWWDObS 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 ineffec- tive in 9 reports.4,5,8,9,13,22 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%.8 OtherWWDdisinfection protocols found to be ineffective included a “phenolic disinfectant,”9 an acetic acid protocol,19 a glucoprotamin protocol,23 and the addition of a vaporized hydrogen peroxide system protocol to other interventions.32 Concomitantly or more usually in the setting of the limited effectiveness of enhanced infection prevention interventions and


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