Novel Immunoassay for Diagnosis of Ongoing Clostridioides difficile Infections Using Serum and Medium Enriched for Newly Synthesized Antibodies (MENSA)

BACKGROUND Clostridioides difficile infections (CDI) have been a challenging and increasing serious concern in recent years. While early and accurate diagnosis is crucial, available assays have frustrating limitations OBJECTIVE Develop a simple, blood-based immunoassay to accurately diagnose patients suffering from active CDI. MATERIALS AND METHODS Uninfected controls (n=95) and CDI patients (n=167) were recruited from Atlanta area hospitals. Blood samples were collected from patients within twelve days of a positive CDI test and processed to yield serum and PBMCs cultured to yield medium enriched for newly synthesized antibodies (MENSA). Multiplex immunoassays measured Ig responses to ten recombinant C. difficile antigens. RESULTS Sixty-six percent of CDI patients produced measurable responses to C. difficile antigens in their serum or MENSA within twelve days of a positive CDI test. Fifty-two of the 167 CDI patients (31%) were detectable in both serum and MENSA, but 32/167 (19%) were detectable only in MENSA, and 27/167 (16%) were detectable only in serum. DISCUSSION We describe the results of a multiplex immunoassay for the diagnosis of ongoing CDI in hospitalized patients. Our assay resolved patients into four categories: MENSA-positive only, serum-positive only, MENSA- and serum-positive, and MENSA- and serum-negative. The MENSA positive-only patients accounted for 30% and may be attributed to nascent antibody secretion in MENSA prior to seroconversion. Conversely, the serum positive-only subset may have been more advanced in their disease course. Immunocompromise and misdiagnosis may have contributed to the 34% of CDI patients who were not identified using MENSA or serum immunoassays. IMPORTANCE While there was considerable overlap between patients identified through MENSA and serum, both methods detected additional, unique patients. The combined use of both MENSA and serum to detect CDI patients resulted in the greatest identification of CDI patients. Together, longitudinal analysis of MENSA and serum will provide a more accurate evaluation of successful host humoral immune responses in CDI patients.