50 Table 3. Description of 12 Cases of Potential Microbiological Bacterial Transfer Eventsa
Patient A B C
Target MDRO
MRSA MRSA VRE
DVREc EVREc FVREc G H I
J
K L
VRE CDI CDI CDI CDI CDI
Total
Terminal Clean Protocol
Bleach Bleach Quat.
Bleach +UV Bleach +UV Bleach +UV Bleach Bleach Bleach Quat. Quat.
Quat. +UV 12
Patient–
Environment X
X X
X X X
X
X X X
X 4 (33%) 4 (33%) 4 (33%) 6 (50%)
nium; CDI, Clostridium difficile infection. aTerminal cleaning protocol used for disinfecting the room prior to admission: bleach, bleach +UV irradiation, Quat., Quat. +UV irradiation. bSubjects could have both molecularly related and molecularly discordant transfer events if>1 ribotype of a target MDRO species was identified. cMolecular relatedness unknown due to noninterpretable pulsed-field gel electrophoresis (PFGE).
Environment– Patient
Presence of Molecularly
Indeterminate X
Related Isolates X X
Presence of Molecularly Discordant MDRO Isolatesb
X X
Luke F. Chen et al
X X
X X
X X X X X
7 (58%) Note. MRSA, methicillin resistant Staphylococcus aureus; VRE, vancomycin-resistant enterococci; MDR ABC, multidrug-resistant Acinetobacter baumanii complex; Quat., quaternary ammo-
600, 700, 800, 1000, or 1100). In 1 patient-to-environmental MBT event, the environmental isolates were identical to the patient- derived isolates and all isolates belonged to pulsotype group III. In a second patient-environmental set in which the direction of MBT was classified as indeterminate, the patient isolates belonged to MRSA pulsogroup I and matched 8 environmental isolates. Interestingly, 4 other types of MRSA were also encountered in the environment, including 2 other distinct pulsotype groups (MRSA groups II and IV) and 2 MRSA singleton isolates (ie, without a molecular match). Five MBT events were VRE related (Tables 3); 1 event was
from patient to environment, 1 event from environment to patient, and 3 other events were indeterminate. While 7 patient isolates were available, they produced only 2 interpretable PFGE patterns, and 91 environmental isolates produced 58 PFGE pat- terns. Among all isolates analyzed, 4 were major PFGE pulsotypes of VRE with at least 2 isolates of>80% similarity, but 14 singleton isolates were identified (Supplemental Fig. 2). Furthermore, the VRE pulsotypes were not shared between different patient– environment sets. For C. difficile, we identified 5 C. difficile-related MBT events;
they produced interpretable ribotype patterns from 8 patient isolates and 23 environmental isolates. Three MBT events involved molecularly related isolates: 2 events were due to environmental to patient transfer and 1 event was due to patient to environment transfer. Also, 2 MBT events involved molecu- larly dissimilar isolates of C. difficile (ie, not true transmissions). Environmental isolates of C. difficile also showed the most variability in ribotype patterns (Supplemental Fig. 3). All patient– environment sets included environmental isolates that had ribo- type patterns different from the patient isolates.
Of the 12 MBT events, time-to-event analyses showed that
80% of the documented transmission, regardless of direction, occurred within 3 days of identifying a target MDRO from any patient or environmental site (Fig. 2).
Specific examples of bacterial transmission events
Several of the observed MBTs were complex and deserve specific narrative beyond aggregated statistical information.
Patient to environment Patient A was colonized with MRSA in the oropharynx and the perineum at study enrollment. At the same initial study visit, none of the environmental surfaces in the patient’s room were contaminated with an MDRO. On study day 3, the oropharyngeal carriage of MRSA was again detected. In addition, a MRSA with identical PFGE pulsotype was also detected from environmental samples obtained from bed rails. This patient did not have a documented HAI with MRSA. Patient B had no MDRO colonization at enrollment. Enroll-
ment samples from recently terminally cleaned environment revealed C. difficile on bathroom floor surfaces. On day 3, the same C. difficile was still detected on the bathroom floor. Sur- prisingly, the patient was asymptomatically colonized with a second and different strain of C. difficile at the same study visit on day 3 (strain B). Patient B developed symptoms of CDI on day 7, and the second strain of C. difficile was detected in stool speci- mens. Subsequently, we found evidence of environmental con- tamination with the second strain of C. difficile on chair arm and in the patient room sink 7 and 14 days following the onset of CDI, respectively. Without sequential patient and environmental
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