Blog | Thursday, May 21, 2015

Punished for precision (or, too much information from the micro lab!)


We recently had a patient's blood culture turn positive for a Gram-positive, catalase-positive, facultative diphtheroid. In the “pre-matrix-assisted laser desorption/ionization (MALDI)” era, we'd have called this isolate a “diphtheroid.” Taking into account other aspects of the case, the National Healthcare Safety Network (NHSN) definition would have categorized this as a contaminant (diphtheroids being on the “common commensal” list maintained by NHSN). By virtue of the wonders of mass spectrometry, we are now able to identify the organism to species-level as Actinomyces neuii, an organism previously categorized as CDC group 1-like coryneform bacteria (also on the “common commensal” list).

A. neuii isn't anywhere on the NHSN organism lists. However, Actinomyces species (as a group) can be found on the “all organisms” list but NOT on the “common commensal” list. The NHSN rules tell us we have to categorize any organism on the “all organisms” list that isn't also on the “common commensals” list as a pathogen, meaning this positive blood culture now helps define a central-line associated bloodstream infection (CLABSI).

And that's the story of how a contaminated blood culture became a CLABSI. We've had other similar cases since we introduced MALDI-time of flight (TOF). Before the CLABSI rate became worth millions of dollars to a hospital's bottom line and reputation, this might have been easy to navigate. Now, though, it's a much bigger deal.

Daniel J. Diekema, MD, FACP, practices infectious diseases, clinical microbiology, and hospital epidemiology in Iowa City, Iowa, splitting time between seeing patients with infectious diseases, diagnosing infections in the microbiology laboratory, and trying to prevent infections in the hospital. This post originally appeared at the blog Controversies in Hospital Infection Prevention.