New CLSI Recommendations: Practical Implications of Eliminating ESBL Testing and Implementing New MIC Breakpoints for Enterobacteriaceae (ENT) at a Major Teaching Hospital

Background:

The CLSI recently published new recommendations for antimicrobial susceptibility testing and reporting for ENT, including lowering of the MIC breakpoints used to classify ENT as susceptible (S), intermediate (I), or resistant (R) to cephalosporins including ceftriaxone (CRO), and elimination of testing for ESBL production.We hypothesized that these recommendations have major implications for Infection Control, in that we require contact precautions (CP) for patients with multidrug-resistant (MDR) organisms based on their reported susceptibilities and ESBL production.

Objective:

To describe the process and practical implications of implementing the new CLSI recommendations at NewYork-Presbyterian Hospital.

Methods:

Before the new CLSI recommendations were implemented, an analysis was performed of E. coli (Ec) and K. pneumoniae (Kp) isolates from 2009 that tested ESBL-positive.  Susceptibilities and MICs were reviewed. From this analysis, a new MDR definition was developed as a proxy for ESBL production, with Ec and Kp isolates I or R to CRO considered MDR.  A second retrospective analysis of Ec and Kp isolates from Jan 2010-Sept 2010 was performed to determine how many additional isolates would be classified as MDR with the new definition and lowered breakpoints and how many additional patients would require CP. Descriptive statistics were performed.

Results:

During the first analysis, we found that all (n=189) isolates for which MIC data were available were I or R to CRO using the new breakpoints. However, because MIC values for ESBL-positive isolates considered S to CRO (based on previous breakpoints) had been suppressed, MIC data were not available for 23% of 141 Ec isolates and 40% of 48 Kp isolates. During the second analysis, we identified 6,026 unique isolates. Using the old breakpoints and ESBL test, 5.7% were defined as MDR or an ESBL-producer. When we applied the new breakpoints and new MDR definition, we found that 8.1% met the MDR definition (p=0.0001); an absolute increase of 2.4%. Relative to the number of isolates that met the old definition, 41% more isolates were considered MDR. Additionally, using the old breakpoints and MDR definition, we found that 5.9% of patients with Ec or Kp isolates required CP. When we applied the revised breakpoints and new MDR definition we found that 8.0% of patients required CP (p<.0001); an absolute increase of 2.1% (i.e., 14 more patients per month) and a relative increase of 35%. The number of patients who had tested ESBL positive but were S to CRO based on the new breakpoints is unknown.

 Conclusions:

After implementing the revised breakpoints, eliminating ESBL testing, and creating a proxy definition for ESBL-producing organisms, the number of isolates considered MDR increased, requiring more patients to need CP, ultimately impacting overall isolation capacity for the hospital.