Association between antibody response to toxin A and protection against recurrent Clostridium difficile diarrhoea

Background We have reported that symptom-free carriers of Clostridium diffi cile have a systemic anamnestic immune response to toxin A. The aim of this study was to determine whether an acquired immune response to toxin A, dur ing an episode of C difficile diarrhoea, influences risk of recurrence. Methods We prospectively studied 63 patients with nosocomial C difficile di arrhoea. Serial serum IgA, IgG, and IgM concentrations against C difficile toxin A, toxin B, or non-toxin antigens were measured by ELISA. Individuals were followed for 60 days. Findings 19 patients died (30%). Of the 44 who survived, 22 had recurrent C difficile diarrhoea. Patients with a single episode of C difficile diarrho ea (n=22) had higher concentrations of serum IgM against toxin A on day 3 o f their first episode of diarrhoea than those with recurrent diarrhoea (n=2 2, p=0.004). On day 12, serum IgG values against toxin A were higher in pat ients who had a single episode of diarrhoea (n=7) than in those who subsequ ently had recurrent diarrhoea (n=9, p=0.009). The odds ratio for recurrence associated with a low concentration of serum IgG against toxin A. measured 12 days after onset of C difficile diarrhoea, was 48.0 (95% CI 3.5-663). Interpretation A serum antibody response to toxin A, during an initial epis ode of C difficile diarrhoea, is associated with protection against recurre nce.