Developing a System to Distinguish C Diff Colonization from Infection Within a Health System


Northwestern Medicine developed a testing strategy using a two-step algorithm to improve diagnostic accuracy and treatment outcomes.

Like many hospitals and health systems in the United States, the Chicago, Illinois-based system, Northwestern Medicine, was challenged with Clostridioides difficile Infections (CDI). Despite their best efforts, the hospital system had high rates of reportable hospital-onset CDI (HO-CDI).

Part of the challenge is the specificity of the PCR test and that it picks up colonization of the C diff bacteria along with acute infection, but not differing the two subsets.

In order to address this issue and try and improve diagnostic accuracy and treatment outcomes for CDI, Northwestern implemented a testing strategy utilizing both a PCR system along with reflex toxin enzyme immunoassay (EIA). They did this across 7 hospitals within their health system.

“The patients [who] were PCR positive would get the enzyme immunoassay, and only if both of those tests were positive would they be counted as a positive C diff case, and then get treatment,” said Radhika Polisetty, PharmD, BCIDP, BCPS AQ-ID, AAHIVP, an associate professor of Pharmacy Practice and infectious diseases specialist at Midwestern University, and who was part of a large team that evaluated this initiative.

Their two-step diagnostic algorithm was done in concert with education, antimicrobial stewardship program (ASP) support and order set changes on HO-CDI rates and C difficile treatment across their health system.

Their study was developed into a subsequent poster, “Impact of a two-step diagnostic bundle on hospital-onset Clostridioides difficile infection rates and treatment across a large health system,” which was presented at the recent ID Week 2022.

“The HO-CDI standardized infection ratio (SIR) reduced significantly from 0.8 to 0.57 p< 0.001), and reportable HO-CDI cases reduced by 238 cases across the health system between May 2021 and March 2022,” Polisetty et al, wrote in their study. “6043 samples were tested, of which 282 (4.7%) were confirmed CDI cases (PCR+/toxin+) and 687 (11%) were non-CDI cases (PCR+/toxin-), of which 438 (67%) received CDI treatment.”

Polisetty was the presenting author and she spoke with Contagion at the conference where she offered some insights into their study, as well as how this can be applied to clinical practice.

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