Investigators examined the latest clinical guideline updates for C difficile testing.
Many patients who are screened for C difficile do not have any other attributable reason for the diarrhea, according to recent findings.
Researchers from the Washington University School of Medicine in St. Louis retrospectively studied a local tertiary-care hospital in order to determine the prevalence of C difficile colonization among patients who met the 2017 IDSA/SHEA C difficile infection Clinical Guideline Update criteria for the preferred patient population for C difficile screening. The guidelines were created by the Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA). Though nucleic acid amplification tests (NAATs) are faster and more sensitive than toxin enzyme immunoassays (EIAs), NAATs may have poor positive predictive value for C difficile.
The new guidelines therefore were designed to test patients with unexplained, new onset, clinically significant, diarrhea with 3 or more unformed bowel movements within a 24-hour period.
In their study, the researchers tested stool specimens with EIA during routine clinical care without any identifiable cause of diarrhea. All patients who screened positive received treatment for C difficile infections (n = 107). Patients who screened negative received C difficile infection antimicrobial treatment within 10 days and were excluded from further analysis if they did not have infection (n = 515). The researchers confirmed they were not infected using a NAAT test to aid in their diagnoses.
The researchers learned that toxigenic C difficile was isolated from a majority of the positive-screened patients (87%). The researchers reported the 3 most common strains of C difficile that were isolated from the positive samples were ribotypes 027, 106/174, and 002.
In the negative patients, toxigenic C difficile was not isolated from a majority of the patients (79%), though toxigenic C difficile was isolated in 12% of the specimens. The most common strains among this cohort were ribotypes 014/020, 027, 001, and 106/174. The study authors also said that none of the patients who screened negative had a clinically confirmed C difficile infection diagnosis within 30 days of their EIA test.
“This finding suggests that toxin EIA has excellent specificity for detecting patients with C difficile infection among patients who meet the preferred C difficile testing population definition,” the study authors wrote. Most importantly, although all patients included in this study met the IDSA/SHEA criteria for the preferred C difficile testing population, the recovery of toxigenic C difficile from these EIA [negative] stool specimens likely represented colonization and not C difficile infection.”
The researchers said that the NAAT detecting C difficile infection from diarrheal stool samples compared to the EIA between 90% and 100%.
“The IDSA/SHEA CDI clinical guideline update recommendations for C difficile testing are stratified based on whether testing can be restricted to patients with unexplained and new-onset clinically significant diarrhea,” the study authors concluded, adding that more research is necessary in order to determine the optimal place for NAAT testing. “The NAAT is recommended as a stand-alone test if testing can be restricted to this population. The purpose of this stratification is because NAATs can detect C difficile colonization among patients with diarrhea for other reasons. However, we found that 12% of patients who met strict criteria for new-onset clinically significant diarrhea and no identifiable alternate cause of diarrhea were colonized with C difficile.”
The study, “Clostridium difficile colonization among patients with clinically significant diarrhea and no identifiable cause of diarrhea,” was published in Infection Control & Hospital Epidemiology.