Culture enhanced toxin detection improves diagnosis of Clostridium difficile infection

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Abstract Objective We aimed to use descriptive epidemiology to clinically validate the use of a sensitive culture-based method for C. difficile toxin detection. Methods We performed a retrospective review of all CDI cases diagnosed at our institution over a three-year period. GDH antigen and direct toxin A/B EIA were tested on all loose stools. GDH-positive but direct toxin-negative samples were cultured on C. difficile agar and resuspended colonies retested using the same toxin EIA kit. Clinical features and outcomes of direct toxin versus culture-enhanced toxin positive cases were compared. Results A total of 251 episodes of CDI were identified in 226 patients. 149 episodes (59.4%) were positive on initial testing, with a further 102 episodes (40.6%) identified after culture. Compared to the direct-toxin group, the culture-toxin group were less likely to have severe CDI by clinical criteria (5.9% vs 16.1%; p = 0.02), laboratory criteria (10.8% vs 22.8%; p = 0.02), and were less likely to receive treatment (67.0% vs 86.8%). All other parameters, including admission length, 30-day mortality, and onset-exposure classification were not statistically different. Using Australian Commission on Safety and Quality in Health Care (ACSQHC) definitions, the rates were 2.59 per 10,000 patient days and 4.39 per 10,000 patient days for direct toxin detection alone and in combination with culture, respectively. Conclusion The culture-enhanced toxin detection method identified an extra 40% of patients harbouring strains of C. difficile capable of producing toxin. It is simple, inexpensive, and uses readily available materials, but may identify some cases that are less clinically severe.