Abstract

Nucleic acid amplification tests are commonly used to diagnose C. difficile infection (CDI). Two-step testing with toxin enzyme immunoassay is recommended to discriminate between infection and colonization but requires additional resources. Prior studies showed that PCR cycle threshold (CT) can predict toxin positivity with high negative predictive value. Starting Oct. 2016, predicted toxin result (CT-Toxin) based on a validated cut-off was routinely reported at our facility. To evaluate the clinical efficacy of this reporting, all adult patients with positive GeneXpert PCR from Oct. 2016 through Oct. 2017 underwent chart review to measure recurrence of or conversion to a CT-Toxin+ result and 30-day all-cause mortality. There were 482 positive PCR tests in 430 unique patients, 282 CT-Toxin+ and 200 CT-Toxin-. Patient characteristics were similar at testing, though CT-Toxin+ patients had a higher WBC count (12.5 v. 9.3 k/µL; p=0.001). All cases (n=21) of fulminant CDI had a CT-Toxin+ result. Index CT-Toxin+ patients were significantly more likely to have a CT-Toxin+ result within 90 days than CT-Toxin- patients (17.4% [n=49] v. 8.0% [n=16]; p=0.003). Thirty-day all-cause mortality was higher in CT-Toxin- patients (11.1% v. 6.8%; p=0.1), though no deaths in CT-Toxin- patients were directly attributable to CDI. Of 200 CT-Toxin- patients, 51.5% (n=103) were treated for CDI. The rate of conversion to a CT-Toxin+ result (8.8% v. 7.2%; p=0.8) and all-cause mortality (8.8% v. 13.4%; p=0.3) were similar between treated and untreated CT-Toxin- patients. CT-based toxin prediction may identify patients at higher risk for CDI-related complications and reduce treatment among CT-Toxin- patients.

View details for DOI 10.1128/JCM.01288-19

View details for PubMedID 31511334