Active Surveillance for Carbapenem-Resistant Enterobacteriaceae in a Long-Term Care Facility

Background: Dissemination of carbapenem-resistant Enterobacteriaceae (CRE) is a concern since these isolates are resistant to nearly all therapeutic agents. Little is known about colonization dynamics among patient populations where CRE infections are identified. In 2008, CR Klebsiella pneumoniae (CRKP) was isolated from urinary tract infections of 4 residents on the same floor of a LTCF. Following the recognition of these infections, residents of the floor were monitored for rectal CRE colonization.

Objective: To determine the prevalence and duration of CRE colonization and to characterize the molecular epidemiology of CRE isolates within this patient population.

Methods: Rectal swabs were collected monthly for 6 consecutive months from each resident and sent to CDC. Specimens were processed according to the surveillance procedure described (www.cdc.gov/ncidod/dhqp/ar_kp.html). A positive culture was defined as isolation of CRE that demonstrated carbapenemase production. CR isolates were typed by pulsed field gel electrophoresis (PFGE) of XbaI-digested DNA as described for E. coli (www.cdc.gov/pulsenet/protocols.html). PFGE patterns were analyzed using BioNumerics.

Results: Rectal swabs (n=217) were cultured from 85 residents. The number of positive cultures compared to the total per month from January to June was: 3/21 (14%), 15/39 (38%), 15/39 (38%), 18/44 (41%), 22/41 (54%), 12/33 (39%). A total of 44 (52%) residents were culture positive and 41 (48%) were negative. Of the positive residents, 10 were persistently positive and 4 were intermittently positive. Three residents were colonized for at least 5 months and 1 for at least 6 months. Only 2 residents appeared to clear colonization (i.e., 2 negative cultures). Thirty-five residents were colonized with CRKP only, 6 were colonized with CRKP and CR E. coli (CREC), and 3 were colonized with either CREC only, CR E. aerogenes, or CRKP and CR K. terrigena. All CRKP PFGE patterns were at least 78.9% similar, suggesting that these isolates were related. Four different CREC PFGE pattern types were identified. Three of these PFGE types were identified in only one resident each, all of whom were also colonized with CRKP. One CREC PFGE type colonized a patient from January to June and was identified in another resident in May, suggesting possible transmission of a colonizing isolate from one resident to another.

Conclusions: CRE colonization was prevalent in this patient population, with up to 54% of the residents colonized 4 months after surveillance was initiated. Colonization in individual residents can persist for at least 6 months. Over time, CRE isolates became more diverse, suggesting transfer of the resistance mechanism between isolates of different genera and transmission of isolates from one colonized resident to another.