Key Point

Co-colonization with MRSA and VRE is occurring in the critically ill, and such cases cannot be detected without routine surveillance cultures.

BALTIMORE—A recent study supports culture screening for methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) in the critically ill, a group at high risk for colonization with both organisms. In the study, a small but significant percentage of ICU patients had co-colonization with MRSA and VRE, and many of these patients were discharged to other institutions.¹

These findings raise the question of whether the co-colonized patients pass their resistant organisms on to other patients. It also highlights the possibility of MRSA/VRE co-colonization becoming more prevalent and leading to increasing rates of vancomycin-resistant S aureus (VRSA) infection.

“Until recently, in the ICU, VRSA was like Armageddon, because there was no treatment,” said Jon P. Furuno, PhD, lead study author and Instructor in the Division of Healthcare Outcomes Research at the University of Maryland School of Medicine in Baltimore. It is believed that MRSA may acquire vancomycin resistance from VRE through the exchange of genetic material, Dr. Furuno told Pulmonary Reviews. He stressed that the co-colonized patients in his study would not have been identified without surveillance cultures.

PROSPECTIVE CASE IDENTIFICATION

To gather information about the prevalence, risk factors, and clinical outcomes associated with MRSA/VRE co-colonization in the critically ill, Dr. Furuno and colleagues prospectively evaluated 2,440 patients admitted to medical or surgical ICUs during a two-year period. For infection control purposes, these patients underwent routine surveillance cultures of the anterior nares for MRSA and of the perirectal area for VRE soon after they were admitted to the ICU.

“Patients may have had multiple admissions during the study period, and all eligible admissions were included in this analysis,” the study authors noted. The authors diagnosed MRSA/VRE co-colonization if both surveillance cultures were positive within 48 hours of ICU admission.

Two hundred forty-seven patients were colonized with VRE and 175 carried MRSA. There were 65 cases of MRSA/VRE co-colonization, yielding an overall rate of 2.7%; there was a 4.6% rate in the medical ICU and a 1.2% rate in the surgical ICU. Further analysis of perirectal cultures from 57 of the co-colonized patients showed that perirectal MRSA/VRE co-colonization was present in 23 (40.4%) of these patients.

In a bivariable analysis, patients colonized with MRSA and/or VRE were more likely than noncolonized patients to have been hospitalized, admitted to the medical ICU, and treated with antimicrobial medications in the year prior to the study. During that interval, 58% of the co-colonized patients were hospitalized, 51% received antimicrobials, about 48% had a positive MRSA culture, and about 28% had a positive VRE culture. About 25% of the co-colonized patients died during the study period.

Independent risk factors for MRSA/VRE co-colonization were increasing age, male gender, antimicrobial therapy in the year before the study, and medical ICU admission in the year before the study, as indicated by odds ratios of 1.03, 1.93, 3.06, and 4.38, respectively.

ARE SURVEILLANCE CULTURES WORTHWHILE?

Some intensivists maintain that surveillance cultures for MRSA/VRE co-colonization are not worthwhile clinically or from a cost perspective, acknowledged Dr. Furuno. “However, none of our co-colonized patients had positive clinical cultures for MRSA and VRE, so the surveillance cultures were important,” he pointed out. “These cases are not just going to jump out at you or be wearing a scarlet letter identifying them as co-colonized.”

Because nearly 35% of the co-colonized patients were discharged to other hospitals or rehabilitation facilities, there appears to be a substantial risk of MRSA and/or VRE transmission to other patients, Dr. Furuno cautioned. The high incidence of perirectal co-colonization among patients carrying MRSA and VRE suggests that there are many opportunities for the two organisms to exchange the genetic material necessary for the appearance of VRSA.

Thus, Dr. Furuno concluded that surveillance cultures are probably advisable in the critically ill and other patients at high risk for carrying MRSA and VRE. For physicians and other health care workers, he recommended awareness of MRSA/VRE co-colonization and the associated risk of VRSA. He also emphasized the need to be prepared to isolate co-colonized patients to prevent the emergence and spread of VRSA in health care institutions.

—Timothy Begany

Reference
1. Furuno JP, Perencevich EN, Johnson JA, et al. Methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci co-colonization. Emerg Infect Dis. 2005;11:1539-1544.

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