Clinical correlates of vancomycin-resistant enterococci/meticillin-resistant Staphylococcus aureus co-colonization and co-infection in Singapore

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.

Wounds, functional disability, and indwelling devices are associated with cocolonization by methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci in southeast Michigan

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) remains sensitive to vancomycin; when vancomycin-resistant S. aureus (VRSA) emerges, treatment becomes more complex. VRSA emergence is attributed to conjugative transfer of the vancomycin-resistance gene cluster from vancomycin-resistant enterococci (VRE) to MRSA. Because cocolonization with MRSA and VRE precedes VRSA development, this study investigates the epidemiology of cocolonization in skilled nursing facility (SNF) residents at high risk for MRSA or VRE colonization.

METHODS

A prospective observational study conducted at 15 SNFs in southeast Michigan. Overall, 178 residents (90 with indwelling urinary catheters and/or feeding tubes and 88 device-free) were cultured monthly for MRSA and VRE, and clinical data were recorded.

RESULTS

The incidence of MRSA/VRE cocolonization among residents with indwelling devices was 6.5 per 100 resident-months; 5.2 (95% confidence interval [CI]: 1.49-18.1) times that among those without devices. MRSA/VRE cocolonization in the device group occurred most frequently in wounds (4.1 per 100 resident-months). In a logistic regression analysis limited to residents with devices, functional disability (rate ratio [RR], 1.3; 95% CI: 1.1-1.4) and wound presence (RR, 3.4; 95% CI: 1.4-8.6) were independent risk factors of cocolonization.

CONCLUSIONS

In a population of SNF residents, individuals with indwelling devices who also had functional disability or wounds were at greatest risk of MRSA/VRE cocolonization. These individuals should be routinely monitored for the presence of VRSA colonization.