Infection Control & Hospital Epidemiology
51 Our baseline microbiological samples from enrolled patients
provided a representative glimpse into the prevalence of MDRO colonization in our subjects. Indeed, 11.3% of the enrolled patients were asymptomatically colonized with at least 1 type of MDRO, a finding consistent with other studies.11 This prevalence underscores the importance of understanding the local anti- microbial susceptibility patterns of organisms to guide appro- priate and effective antibiotic choice. The baseline microbiological cultures from environmental
Fig. 2. Time-to-event analysis showing time from first positive bacterial culture from any source to documented transfer of clonally identical bacteria between patients and room surfaces.
sampling and the molecular confirmation, the environment would have been blamed as the source for C. difficile acquisition and infection.
Environment to patient Neither Patient C nor the environmental surfaces were colonized with any of the marker MDROs at enrollment. On day 3, C. difficile isolates were detected on the sink and the bed rail. On day 14, the patient’s perineal specimen showed the same clonal type of CDI as that recovered on day 3 from the environmental specimen. The patient remained asymptomatic for CDI throughout the duration of the study and the hospital stay.
Discussion
We used a prospective study design and molecular techniques to study the transmission of MDROs between patients and surfaces of hospital rooms. The most important finding from the current study is the demonstration of microbiological bacterial transfer events in 12 patient encounters (18.5%) from the ME cohort (Fig. 1). Molecular testing of specimens showed that 6 encounters (66.7% of the 9 ME cohort with molecular data and 9.2% of the 65 evaluable patients) involved molecularly identical strains of MDRO. Indeed, 7.5% of all hospital-room encounters showed transfer of clonally identical MDROs. Perhaps most importantly, we identified 2 encounters (3%) in which the patient acquired an MDRO present in the environment at the time of admission; both events were confirmed environment-to-patient transmissions involving C. difficile. We believe that these observed rates of MDRO transmission
are underestimates of the true bacterial transfer phenomenon for 2 primary reasons: (1) limitations in sampling and (2) lack of sensitivity of current microbiological methods. Furthermore, we only tracked bacterial transmission using 4 ‘marker’ MDROs; we hypothesize that bacterial transmission occurs at a larger scale in real-life healthcare settings, involving wild-type species and organisms of varying drug-resistances, such as those that have extended-spectrum β-lactamase (ESBL), TEM and SHV, or AmpC resistance determinants.
sources showed that 55% of hospital patient rooms still had at least 1 surface with detectable microbial growth of MDROs at time of patient admission despite terminal disinfection proce- dures. The average level of surface contamination was low but was clearly sufficient for documented transmission to patients. These environmental microbiological data from our study add weight to recent investigations showing that the carrier status of a room’s prior occupant can increase risk of MDRO acquisition for the subsequent occupant.12,13 These results support the urgency of investigating and implementing enhanced terminal-cleaning procedures to further reduce residual microbial contamination during patient room turnover and to minimize the risk of bac- terial transmission.4 Finally, these findings occurred despite concurrent application of enhanced terminal room disinfection strategies and high rates of compliance of surface cleaning.4 Our observation of low-level bacterial contamination after
terminal cleaning highlights another important limitation in current literature; there is no consensus method for assessing or defining a surface as “clean.” 14 The establishment of a definition or target of “clean” surface is difficult, but it is needed for future technologies and real-world interventions to reduce risk for pathogen transmission.14 Throughout the hospital stay, we observed that hospital room
surfaces became contaminated withMDROs. We hypothesized that these new environmental isolates were introduced during the hos- pitalization through one or a combination of the following sources: importation through healthcare staff, contaminated fomites brought into the room (eg, trays, medical equipment, etc.), visitors, or unmasking of prior bacterial colonization of the patient through triggers such as antibiotic selection pressure. Where bacterial- transmission events were noted, most occurred early (within 3 days) into the admission of a newly cleaned room. Furthermore, bacterial transmission from the environment resulted in both asymptomatic carriage and symptomatic infection among the patients. The early transmission of MDRO between the environment and patient is an important observation and points to the opportunity for develop- ment of effective prevention strategies of bacterial transmission.15,16 Our study was limited by the modest number of patients and
rooms we could feasibly enroll and study using microbiological and molecular techniques. The representativeness of our study of usual clinical practice was also potentially lowered because the study targeted rooms that previously housed patients on contact precautions. Second, our microbiological sampling was not always timed to occur before daily cleaning by environmental services staff; thus, some surfaces may have been freshly cleaned prior to sampling. Furthermore, we recognize that external vectors could introduce organisms to the hospital room environment and the patient throughout the study period (eg, healthcare staff or visi- tors). However, other factors also counterbalance these external forces and reduce detection of transferred organisms, such as treatment with concurrent antibiotic and/or a high hand hygiene performance rate that is greater than published literature (>90% compliance).17 We believe that these limitations suggest that our
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