Poor Sensitivity of NHSN Surveillance Definition of CLABSI

Background: Public reporting of CLABSI data will begin in 2011 using the NHSN surveillance definition (SD). The goal is to achieve zero CLABSIs.  Thus it is crucial that that the CLABSI definition be a meaningful measure of the true incidence of CLABSIs. Despite implementation of the "central line" bundle, CLABSIs persist in most hospitals.  This may in part due to a lack of specificity of the SD.

Objective: To determine the positive predictive value (PPV) of the NHSN CLABSI surveillance definition versus  a clinical definition of CLABSI (CD) based on a careful chart review by an experienced Infectious Disease physician. 

Methods:  All cases meeting the NHSN definition of CLABSI at our health system for the first three quarters of 2010 were tabulated. Cases were identified by ICPs using microbiology laboratory results and chart review and validated by an Infectious Disease physician.  Medical records of each case was then reviewed by the same Infectious Disease physician to determine if the BSI was related to the central line or other potential sources.  Factors considered included vital signs, underlying medical conditions, prior antimicrobial therapy, clinical progress notes, radiographs, and number of positive blood cultures, and results of semi-quantitative catheter tip cultures.

Results: Only 9 of 15 cases meeting the HNSN SD of CLABSI met the CD of CLABSI.  The PPV of the SD was only 60%.  The causes of discordance were: 1. positive blood cultures within 24 hours of catheter insertion (one case), 2. single positive blood culture for VRE (2 cases), 3. single positive blood culture for candida in ICU patient on prolonged broad-spectrum antibiotics (1 case), 4. intermittently positive blood cultures for candida in leukemic patients with febrile neutropenia (2 cases). These were all judged to be either contaminants or due to GI source on clinical review. 

Conclusions: The current NHSN SD lacks specificity for CLABSI. Elimination of CLABSIs may not be possible with this definition. Based on this data, the PPV of the SD could be improved greatly by three simple modifcations. 1. excluding blood cultures obtained within 24 hr of line insertion, 2. requiring ≥ 1 positive blood culture for all pathogens, not just for common contaminants, and 3. excluding patients with neutropenia (<500 PMN/mm3). The NHSN should consider revising the SD to increase the PPV. Reported rates would then more accurately reflect the true incidence of CLABSI, and prevention efforts focused on cases that are truly preventable.