Blog | Wednesday, July 9, 2014

The enemy within


There are a couple studies out, 1 in Clinical Infectious Diseases (from WashU) and 1 in Infection Control and Hospital Epidemiology (from Houston), that carry the same message: a substantial portion (13-15%) of asymptomatic hospitalized adults carry toxigenic strains of Clostridium difficile in their gastrointestinal tracts. Coming on the heels of this New England Journal of Medicine study using whole-genome sequencing to describe the genetic diversity of C. difficile strains, these studies advance an evolving narrative that many cases of C. difficile-associated disease (CDAD) are not attributable to in-hospital transmission from other symptomatic patients (and thus are impervious to transmission-prevention approaches such as hand hygiene, contact precautions, and enhanced environmental disinfection). The major take-away point for me: it’s all about the stewardship! Knowing that 15% of patients harbor toxigenic C. difficile should only increase the urgency of antimicrobial stewardship efforts.

The other major implication of these studies relates to the predictive value of highly sensitive polymerase chain reaction (PCR) tests that target the toxin gene(s). To quote from the authors’ conclusion in Koo, et al:

“In the health care setting, where the majority of diarrhea cases are not attributable to CDAD and the prevalence of asymptomatic C. difficile colonization is greater than the frequency of CDAD, NAAT (nucleic acid amplification test) detection of asymptomatic colonization among health care-associated diarrhea patients may be contributing to a significant number of CDAD false positives.”

The UK have already changed their surveillance recommendations to require a toxin enzyme-linked immunosorbent assay as confirmation of every positive PCR test. With lab-identified C. difficile now publicly reportable, I suspect more U.S. centers will switch to 2-step algorithms and/or begin restricting access to PCR-based assays to reduce the false positivity problems.

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.