Surveillance strategies and impact of vancomycin-resistant enterococcal colonization and infection in critically ill patients

Abstract

Objective: To determine the optimal site and frequency for vancomycin-resistant enterococci (VRE) surveillance to minimize the number of days of VRE colonization before identification and subsequent isolation.

Summary background data: The increasing prevalence of VRE and the limited therapeutic options for its treatment demand early identification of colonization to prevent transmission.

Methods: The authors conducted a 3-month prospective observational study in medical and surgical intensive care unit (ICU) patients with a stay of 3 days or more. Oropharyngeal and rectal swabs, tracheal and gastric aspirates, and urine specimens were cultured for VRE on admission to the ICU and twice weekly until discharge.

Results: Of 117 evaluable patients, 23 (20%) were colonized by VRE. Twelve patients (10%) had VRE infection. Of nine patients who developed infections after ICU admission, eight were colonized before infection. The rectum was the first site of colonization in 92% of patients, and positive rectal cultures preceded 89% of infections acquired in the ICU. This was supported by strain delineations using pulsed-field gel electrophoresis. Twice-weekly rectal surveillance alone identified 93% of the maximal estimated VRE-related patient-days; weekly or admission-only surveillance was less effective. As a test for future VRE infection, rectal surveillance culture twice weekly had a negative predictive value of 99%, a positive predictive value of 44%, and a relative risk for infection of 34.

Conclusions: Twice-weekly rectal VRE surveillance of critically ill patients is an effective strategy for early identification of colonized patients at increased risk for VRE transmission, infection, and death.

Figure 1. Schematic of vancomycin-resistant enterococci events. The denominator for the percentages is the number in the branch immediately above the percentage.

Figure 2. Pulsed-field gel electrophoresis (PFGE) of colonization/infection pairs. PFGE of SmaI DNA digests of paired vancomycin-resistant enterococci isolates from nine patients with infection acquired in the intensive care unit. First colonizing rectal isolates are designated 1R to 9R. The corresponding first-infected site isolate from the same patient is designated 1I to 9I. End lanes contain NotI-digested Enterococcus faecalis OGIRF molecular weight marker. Band sizes are shown to the left in kilobase (kb) pairs. Patients 1 to 4 are in panel A, patients 5 to 9 in panel B.