Necessity of nucleic acid amplification test and toxigenic culture in the diagnosis of Clostridioides difficile

Abstract

The Nucleic Acid Amplification Test (NAAT) is now covered by insurance as a test for Clostridioides difficile infection (CDI). However, it has not been established whether culture and toxigenic culture (TC) test should be performed in conjunction with NAAT, and we investigated the necessity of these tests. The subjects were 336 diarrhea samples submitted for detection of Clostridioides difficile antigen (GDH) and toxin: The number of GDH-positive/toxin-positive cases were 10, GDH-positive/toxin-negative cases were 32, and GDH-negative/toxin-negative cases were 294．Of the 13 GDH-positive/toxin-negative and NAAT-negative cases, the 7 culture-positive cases were all TC test negative. This suggested that there was little necessity for additional TC testing in the case of GDH-positive/toxin-negative and NAAT-negative. Among 294 GDH-negative/toxin-negative cases, NAAT-positive cases were 1.7% (5/294) and TC test-positive cases were 4.1% (12/294). Although the likelihood of positive NAAT or TC tests in GDH-negative/toxin-negative cases is low, CDI may be present, and TC test or NAAT may be considered, especially if CDI is strongly suspected.