Determining the clinical significance of co-colonization of vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus in the intestinal tracts of patients in intensive care units: a case-control study.

Background: The emergence of vancomycin-resistant Staphylococcus aureus (VRSA) has become a global concern for public health. The proximity of vancomycin-resistant enterococcus (VRE) and methicillin-resistant S. aureus (MRSA) is considered to be one of the foremost risk factors for the development of VRSA. This study aimed to determine the incidence, risk factors, and clinical outcomes of intestinal co-colonization with VRE and MRSA.

Methods: A case-control study was conducted in 52-bed intensive care units (ICUs) of a university-affiliated hospital from September 2012 to October 2017. Active surveillance using rectal cultures for VRE were conducted at ICU admission and on a weekly basis. Weekly surveillance cultures for detection of rectal MRSA were also conducted in patients with VRE carriage. Patients with intestinal co-colonization of VRE and MRSA were compared with randomly selected control patients with VRE colonization alone (1:1). Vancomycin minimum inhibitory concentrations (MICs) for MRSA isolates were determined by the Etest.

Results: Of the 4679 consecutive patients, 195 cases and 924 controls were detected. The median monthly incidence and duration of intestinal co-colonization with VRE and MRSA were 2.3/1000 patient-days and 7 days, respectively. The frequency of both MRSA infections and mortality attributable to MRSA were higher in the case group than in the control group: 56.9% vs. 44.1% (P = 0.011) and 8.2% vs. 1.0% (P = 0.002), respectively. Independent risk factors for intestinal co-colonization were enteral tube feeding (odds ratio [OR], 2.09; 95% confidence interval [CI] 1.32-3.32), metabolic diseases (OR, 1.75; 95% CI 1.05-2.93), male gender (OR, 1.62; 95% CI 1.06-2.50), and Charlson comorbidity index < 3 (OR, 3.61; 95% CI 1.88-6.94). All MRSA isolates from case patients were susceptible to vancomycin (MIC ≤ 2 mg/L).

Conclusions: Our study indicates that intestinal co-colonization of VRE and MRSA occurs commonly among patients in the ICU with MRSA endemicity, which might be associated with poor clinical outcomes.