Host Immune Markers Distinguish Clostridioides difficile Infection From Asymptomatic Carriage and Non–C. difficile Diarrhea

Background Recent data indicate that Clostridioides difficile toxin concentrations in stool do not differentiate between C. difficile infection (CDI) and asymptomatic carriage. Thus, we lack a method to distinguish a symptomatic patient with CDI from a colonized patient with diarrhea from another cause. To address this, we evaluated markers of innate and adaptive immunity in adult inpatients with CDI (diagnosed per US guidelines), asymptomatic carriage, or non-CDI diarrhea. Methods CDI-NAAT patients had clinically significant diarrhea and positive nucleic acid amplification testing (NAAT) and received CDI treatment. Carrier-NAAT patients had positive stool NAAT but no diarrhea. NAAT-negative patients (with and without diarrhea) were also enrolled. A panel of cytokines and anti–toxin A and B immunoglobulin (Ig) were measured in serum; calprotectin and anti–toxin B Ig A/G were measured in stool. NAAT-positive stool samples were tested by an ultrasensitive toxin assay (clinical cutoff, 20 pg/mL). Results Median values for interleukin (IL)-4, IL-6, IL-8, IL-10, IL-15, granulocyte colony-stimulating factor (GCSF), MCP-1, tumor necrosis factor α (TNF-α), and IgG anti–toxin A in blood and IgA/G anti–toxin B in stool were significantly higher in CDI patients compared with all other groups (P < .05). Concentration distributions for IL-6, GCSF, TNF-α, and IgG anti–toxin A in blood, as well as IgA and IgG anti–toxin B in stool, separated CDI patients from all other groups. Conclusions Specific markers of innate and adaptive immunity distinguish CDI from all other groups, suggesting potential clinical utility for identifying which NAAT- and toxin-positive patients with diarrhea truly have CDI.