Laboratory Practices Survey for Carbapenem Resistant Gram Negative Bacilli in Arizona, 2011-2013

BACKGROUND:   Carbapenem resistant organisms (CRO) are an increasing public health concern due to challenges they present in managing patient treatment and outcomes as well as their capacity for healthcare and community transmission.  Rapid identification of carbapenem resistance from Gram-negative organisms is essential for appropriate patient care and implementation of infection control and prevention measures.  Various methods exist to identify CROs, and laboratories use multiple guidelines and definitions for their classification.  Facilities applying different sources or non-current Clinical and Laboratory Standards Institute (CLSI) Guidelines to interpret antibiotic susceptibility results may disparately identify CROs.  In response to these concerns, the Arizona Department of Health Services (ADHS) initiated a series of projects to characterize the epidemiology of CRO, specifically carbapenem resistant Enterobacteriaceae (CRE) in Arizona, including a state-wide Laboratory Practices Survey (LPS) to assess clinical laboratory methods and capacity for CRE testing.

METHODS:   In July, 2011, Arizona laboratory directors and infection preventionists were contacted to complete a survey either online or by telephone interview.  Laboratories performing CRO testing or assessing Gram-negative bacilli susceptibility results were included in the study.  Survey questions addressed the following: CRO susceptibility testing methods, performance standards, and reporting notification practices.

RESULTS:   Sixty-three eligible facilities were asked to respond to the LPS, yielding 41 (65.1%) valid responses.  Over 60% (26) of responding facilities identified at least one CRE isolate per quarter.  Four facilities identified between six to twenty isolates per quarter, all located in Arizona’s most populous county.  All facilities indicated that they perform automated susceptibility testing for suspected CRE, either in-house or through a reference lab.  In addition, 10 (24.4%) facilities use further testing to obtain carbapenem minimum inhibitory concentration values, and 26 (63.4%) facilities confirm carbapenemase production using modified Hodge Test (MHT).  Over half (25) of facilities were applying M100-S20 CLSI Performance Standards, or more current.

CONCLUSIONS:   Respondents in all four regions of the state indicated identification of CRE within their facilities, with more CRE identified in the central region.  Arizona laboratories rely heavily on automated susceptibility systems to initially identify CROs, however there is not uniform application of methodologies or definitions to classify or confirm resistance.  Many facilities apply non-current guidelines and practices, which may lead to inaccurate classification of CROs.  Further analysis of CRE isolates in Arizona is needed to validate automated susceptibility classifications and to characterize the burden of CRE in Arizona.  A Follow-up CRO LPS is planned for early 2013.