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Methods Study design and study population
We present data collected as part of a multicenter, prospective, observational study reporting the frequency of, and risk factors for, the contamination of HCP gloves and gowns when providing care to residents of community nursing homes. We previously reported data describing MRSA transmission in this population.9 This report describes transmission of RGNB in the same cohort. The institutional review boards of the University of Maryland and the University of Michigan approved this protocol.9 Residents from 13 non-VA community-based nursing facilities
in Maryland (n=10) and Michigan (n=3) were approached for enrollment.9 Eligible residents were enrolled with written informed consent from them (84%) or their legally authorized representative (16%). HCP were enrolled with verbal consent.9
Data collection
A research coordinator recorded demographic and clinical char- acteristics from enrolled residents, including the activities of daily living (ADL) score. The ADL score includes bed mobility, transfer, toilet use and eating. A total ADL score ranges between 0 and 16. A score of 0 represents an independent resident, in contrast to a score of 16, which represents a totally dependent resident.12 A perianal swab was collected only once from each participating resident at enrollment. As part of the study, we asked HCP to wear gowns and gloves during usual care activities. The research coordinator observed and recorded the types of care delivered during each interaction (which may have included 1 or >1 type of care). When each HCP was finished with care activ- ities, the coordinator swabbed the gloves and gown in a stan- dardized manner before they were removed completely, and the HCP interacted with a different resident. A single set of gloves and gown was worn during each interaction.9
Laboratory analysis
Residents’ perianal swabs and HCP gown and gloves swabs were enriched by inoculating 100 µL E-swab liquid into 5mL BHI broth and incubated 24 hours at 35–37°C in ambient air. This solution was later cultured on each of the following plates: MacConkey agar supplemented with 1 µg/mL ciprofloxacin; MacConkey agar supplemented with 1 µg/mL ceftazidime; and MacConkey agar supplemented with 1 µg/mL imipenem. Plates were streaked for isolation and incubated aerobically at 37°C for 24 hours. Identification was confirmed using VITEK II system (BioMérieux, Hazelwood, MO). The Kirby-Bauer test was used to confirm each organism’s susceptibility to antibiotics. Organisms were categorized as susceptible, intermediate, or resistant based on the Clinical Laboratory Standards Institute’s (CLSI) breakpoints.13
Study definitions
The RGNB were defined as any pathogenic gram-negative bac- teria categorized as intermediate or resistant based on the Kirby- Bauer test for at least 1 of the following antibiotics: ciprofloxacin, ceftazidime, or imipenem.13 Residents were considered colonized with RGNB if their perianal culture was positive for at least 1 RGNB. Transmission to gowns and/or gloves with RGNB occurred when at least 1 strain isolated from the HCP gown or gloves matched the genus, species, and antibiotic resistance
Natalia Blanco et al
pattern of the strain isolated from the respective RGNB-colonized resident.10
Statistical analysis
Resident characteristics were described using proportions for categorical variables and median and range (minimum–max- imum) for continuous variables. The overall crude transmission rate was estimated as the number of HCP interactions that led to RGNB transmission over the total number of HCP interactions. Overall transmission rate to HCP (1) gown or gloves, (2) gloves only, and (3) gown only were estimated. Additionally, the crude rate of transmission by type of care was estimated as the total number of HCP interactions that led to transmission during a particular type of care over the total number of HCP interactions of this particular type of care. Logistic regression, using general- ized estimating equations (GEEs)14 to account for the correlation of repeated measures within resident, was used to estimate the odds ratio (OR) associated with each type of care and resident characteristics. The OR, for example, gives the odds of RGNB transmission to the HCP gloves or gown when a resident receives a particular type of care divided by the odds of RGNB trans- mission when the resident receives care other than the particular type of care being examined. Types of care or resident char- acteristics with an OR >1.0 and P<.05 for a specific type of care were considered high risk. Additionally, types of care or resident characteristics with strong ORs above 2.5, even if not statistically significant, were considered high risk.
Results Resident characteristics
A perianal swab was collected from 399 of the 403 enrolled residents (99%). Among the 399 residents, 221 residents were enrolled in Maryland and 178 in Michigan. No significant dif- ference in median age or gender was observed between both states.
Among 399 residents, 74 (19%) were colonized with at least 1
RGNB on their perianal skin at enrollment (Table 1). Colonized residents were more likely to be receiving rehabilitation care than noncolonized residents (51% vs 37%; P=.03). Colonized resi- dents also had a higher median ADL score than noncolonized residents (9 vs 7; P<.01).
Microbiological characteristics
In total, 110 RGNB were isolated from the residents’ perianal swabs. Of these, 92 (84%) belonged to the Enterobacteriaceae family, 13 (12%) were Pseudomonas aeruginosa, and 5 (4%) were Acinetobacter baumannii. Among the 92 isolates from Enter- obacteriaceae family, 80 (87%) were resistant to ciprofloxacin, 21 (23%) were resistant to ceftazidime, and 28 (30%) were resistant to imipenem. Among the 13 P. aeruginosa isolates, all were resistant to ciprofloxacin, 3 (23%) were resistant to ceftazidime, and 7 (55%) were resistant to imipenem. Among the A. baumannii isolates (n=5), all were resistant to
ciprofloxacin, 4 (80%) were resistant to ceftazidime, and 3 (60%) were resistant to imipenem. Similarly, among these 110 resistant isolates, 67 isolates (61%) were resistant to only 1 of the analyzed antibiotics, while 39% were resistant to 2 or more antibiotics.
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