Comparison of enzyme immunoassays and rapid diagnostic tests for clostridium difficile glutamate dehydrogenase and toxin a + B to toxinogenic culture on a highly selective chromogenic medium.

To compare Clostridium. (C.) difficile toxin A/B and glutamate dehydrogenase (GDH) enzyme immunoassays or rapid diagnostic tests to toxinogenic culture on recently described highly selective agar plates. Five hundred consecutive samples sent in for C. difficile diagnostics were tested by toxin A/B enzyme immunoassay (EIA) and rapid diagnostic test (RDT), GDH EIA and RDT, and culture on chromID C. difficile plates for 48 hrs, with toxin testing from culture if the toxin EIA from feces was negative. Samples with discordant results from EIA and RDT were submitted to C. difficile-specific 16S rRNA gene and tcdB PCR. Ninety-two, 88, 31, and 37 samples were positive by GDH EIA, GDH RDT, toxin A/B EIA, and toxin A/B RDT respectively. Seventy-four samples were positive by culture, 54 culture-positive samples were subjected to repeat toxin testing, with an additional 29 samples positive. Thus, there were 60 C. difficile toxin A/B positive samples in total (12 %). Single-step screening with GDH EIA, GDH RDT, toxin A/B EIA, and toxin A/B RDT would have missed seven (12 %), 11 (18 %), 29 (48 %) or 27 (45 %) of all positive samples respectively. Single-step screening with GDH or toxin A/B tests from feces misses a significant proportion of patients compared to toxinogenic culture, putting these patients at risk from undiagnosed C. difficile infection. More data are needed to establish the clinical significance of a positive toxinogenic culture result in the absence of detectable toxin A/B in feces.