Transfer of Extended Spectrum Cephalosporin Resistant Enterobacteriaceae Among Patients on an HSCT Unit and the Value of Surveillance and Contact Isolation

Abstract

The mechanism(s) of acquisition of extended-spectrum cephalosporin-resistant Enterobacteriaceae (ESCRE) on inpatient hospital units dedicated to hematopoietic stem cell transplantation (HSCT) is unclear. The objectives of this study were to determine whether ESCRE organisms are transmitted among patients housed on a HSCT unit, clarify the mechanisms involved, and determine whether routine surveillance for ESCRE carriage and contact isolation for ESCRE carriers is beneficial. The study was conducted on a 30-bed inpatient unit dedicated to the care of patients with hematologic malignancies and HSCT recipients. To investigate whether ESCRE organisms may be transmitted vertically to subsequent room occupants, presumably through contamination of room surfaces, we (1) cultured 6 high touch areas in 10 rooms before and 9 rooms after terminal cleaning that had been occupied by patients with ESCRE carriage, (2) determined the in vitro survivals of our most common clinical ESCRE species, and (3) followed the subsequent room occupants of 54 consecutive ESCRE colonized patients for the development of inpatient acquired ESCRE carriage. To investigate whether ESCRE organisms are transmitted horizontally among inpatients we (1) sequenced 60 available ESCRE Escherichia coli isolates obtained from unit inpatients and searched for identities using complete-genome multisequence locus typing (cgMLST) and (2) retrospectively tabulated the cumulative rates of acquired ESCRE carriage in 356 patients admitted for a first HSCT before (200 patients) or after (156 patients) institution of universal ESCRE stool surveillance and contact isolation for carriers. No ESCRE organisms were cultured from patient rooms before or after terminal cleaning. In vitro, few, if any, ESCRE organisms survived longer than 2 hours. Nine of the subsequent occupants of a room in which a patient with ESCRE carriage had resided were detected with ESCRE carriage, only 2 of whom carried the same species as that of the prior occupant. DNA sequencing and cgMLST determination of the 60 E. coli isolates showed 53 cgMLST strains. Seven of the 53 strains were shared by 2 patients. After institution of universal ESCRE surveillance/isolation there was a significant decline in acquired ESCRE carriage among HSCT recipients. We conclude that vertical transmission of ESCRE organisms through room contamination appears to be uncommon on modern HSCT units. Conversely, our results are consistent with the horizontal spread of ESCRE organisms, probably mediated by intermediate vectors such as personnel or shared equipment. Further studies are needed to better define the magnitude of and risk factors for ESCRE horizontal transfers and the benefits of ESCRE surveillance/isolation.