This study was conducted in the 29-bed medical and 19-bed surgical intensive care units at the University of Maryland Medical Center (Baltimore) in August and September 2008. In both units, MDR A. baumannii and MDR P. aeruginosa are endemic. The study was approved by the Institutional Review Board of the University of Maryland, Baltimore.
Patients were identified as colonized with MDR A. baumannii or as colonized with both MDR A. baumannii and MDR P. aeruginosa as a part of routine care on the basis of active surveillance or by the results of clinical cultures performed during their index hospitalization (upon identification, they were placed under contact precautions). Active surveillance, when used, consisted of culturing specimens obtained from the sputum, groin, perirectal area, and wound, if present. In our hospital, contact precautions are used for all patients infected with MDR A. baumannii that is susceptible to no more than 2 antimicrobial classes and for all patients infected with MDR P. aeruginosa that is susceptible to no more than 1 antimicrobial class, excluding tigecycline or polymyxin (all isolates of either species were imipenem resistant). HCWs (registered nurses, patient care technicians, respiratory therapists, occupational or physical therapists, and physicians) were approached for participation in the study before they engaged in routine, nonemergent clinical care activities for these patients.
Cultures were performed as described previously.10
In brief, sterile cotton-tipped applicators (220093 CultureSwab; Becton Dickinson) were moistened with liquid Amies transport media (Becton Dickinson). Hand and glove samples were obtained with a standardized process, by swabbing the dorsum of each finger 3 times and the palm of each hand 2 times with a twirling motion of the swab; a single swab was used for both hands or both gloves. Gowns were sampled by swabbing each forearm twice and then swabbing a “W” along the belt line, all with a single swab and performed with a twirling motion. Hands were first sampled before the HCW donned gown and gloves. Data from observations in which HCW hands were colonized before room entry were excluded from the analysis. HCW activities were observed and documented, including the duration and nature of HCW-patient contact. Upon completion of activities and before the HCW exited the patient room, the HCW gloves and gown were swabbed by investigators. The bare hands of the HCWs were immediately sampled a second time, before hand hygiene.
Swab samples were vortexed in 5 mL of brain-heart infusion broth with imipenem, 6 μg/mL (imipenem was added to enhance detection of MDR A. baumannii and MDR P. aeruginosa, because all isolates were carbapenem resistant). Broths were kept at 35°C overnight. Then, 50 μL of the broth was plated to MacConkey agar with and without imipenem, 6 μg/mL. Plates were incubated overnight at 35°C. Non–lactose-fermenting colonies were subcultured to trypticase soy agar with 5% sheep blood. Oxidase-negative isolates were identified as A. baumannii by analytical profile index 20E test strip or Vitek II (bioMérieux). Oxidase-positive isolates were subcultured onto triple sugar iron (TSI) and Pseudomonas agar (P-agar) slants. TSI slants were incubated overnight at 35°C, and P-agar slants were kept at 42°C overnight. P. aeruginosa isolates were identified as K/K on TSI slants and were pyocyanin-producing on P-agar.
Pulsed-field gel electrophoresis (PFGE) was performed on A. baumannii
isolates in accordance with a protocol described elsewhere,11
In brief, DNA was digested with Apa
I in accordance with manufacturer recommendations (New England Biolabs). DNA was separated in 1% agarose on a contour-clamped homogeneous-field machine (CHEF-DR II; Bio-Rad). Electrophoresis was performed at 6 V/cm for 18.5 hours, with pulse times ranging 7–20 seconds. After electrophoresis, gels were stained with ethidium bromide and were photographed under ultraviolet illumination. Photographic images of gels were saved digitally with the Geldoc EQ (BioRad) and saved as TIFF files for gel analysis with Gel Compare (Applied Math). The resulting band patterns were compared with the Dice coefficient 100 by means of the unweighted pair group method to define pulsed-field type clusters, in accordance with the criteria established by Tenover et al.13
Risk factor analysis was conducted using the Fisher exact test to measure the significance of associations between binary variables and the dependent variable of MDR A. baumannii contamination of gowns or gloves. Time in room was non-normally distributed (mean, 8.5 minutes; median, 5.0 minutes; interquartile range, 3.0–9.0 minutes); therefore, time was dichotomized about the median for further analysis to have a more meaningful metric than would be obtained with log transformation. A logistic regression model was constructed, adding potential confounders one by one, in the order of most significant association on bivariate analysis (ie, lowest P value). The change in the β coefficient for wound care for each model was observed, and the covariate was included if the change was greater than 5%. The Breslow-Day test was used to assess for interactions. We report adjusted odds ratios (aORs) and 95% confidence intervals (CIs) from the multivariate logistic regression model. All statistical tests were 2-sided; P < .05 was considered to be statistically significant. All analyses were performed using SAS, version 9.1 (SAS).
The frequency of MDR A. baumannii isolation from HCWs’ protective equipment was used to estimate the risk of HCW contamination. This information was combined with differential adherence to contact precautions and hand hygiene. For this estimate, we assumed that eradication of MDR A. baumannii with hand hygiene was 100% and that adherence to contact precautions and adherence to hand hygiene after glove removal were independent.