Evaluation of a Fluorescence Immunoassay for Detection of Clostridioides difficile Glutamate Dehydrogenase and Toxin Antigens

Background: Clostridioides difficile infection (CDI) is a leading cause of nosocomial infections in the United States, causing longer hospital stays, significant morbidity, and increased healthcare costs. Accurate CDI diagnosis is essential for timely treatment and infection control. Laboratory diagnosis of CDI commonly involves the detection of glutamate dehydrogenase (GDH) and/or toxins A and B by immunoassays or the toxin genes by nucleic acid amplification. This study assesses the performance of a new commercial test, the Sofia® 2 C. difficile Fluorescent Immunoassay (Sofia 2; FIA; QuidelOrtho), for detecting C. difficile GDH and toxins. Methods: Sofia 2 was compared to enzyme immunoassays (EIAs) C. diff Quik Chek Complete (Techlab Inc.) and Immunocard (Meridian Bioscience) using remnant stool samples from 262 patients with suspected CDI. Results: Sofia 2 demonstrated high agreement with the EIA methods for GDH (positive percentage agreement (PPA): 100%, negative percentage agreement (NPA): 94%, overall percentage of agreement (OPA): 95%) and toxins (PPA: 100%, NPA: 99%, OPA: 99%) detection. Compared to standard-of-care (SOC) testing including toxin gene PCR with the following toxin antigen test, Sofia 2 demonstrates strong PPA (100%), NPA (98%), positive predictive value (71%), and negative predictive value (100%). Conclusions: Sofia 2 C. difficile FIA generates rapid results that are comparable to other commercial immunoassays with a simple workflow, supporting its use for CDI diagnosis in clinical practice.