Evaluation of the Use of Rectal Swabs for the Laboratory Diagnosis of Clostridium difficile Infection

ABSTRACT Background: For the diagnosis of Clostridium difficile infection (CDI), microbiological testing is almost always accomplished through analysis of stool specimens. We evaluated the performance of rectal swabs with liquid transport medium (FS) and nylon flocked dry swabs for the detection of C. difficile. Additionally, the impact on the diagnostic yield of storing swabs at -80°C for up to three months was evaluated.

Methods: Sixty clinical stool samples positive for C. difficile by PCR were used for simulating rectal swabbing. FS and dry swabs were dipped into the stool and tested by PCR directly after swabbing, one and three month after storage at -80°C. Stool and the liquid medium of FS were additionally tested by a combination of glutamate dehydrogenase antigen (GDH) testing and toxin A/B EIA, and by toxigenic culture (TC).

Results: Using dry swabs the PCR-based detection rate of C. difficile was equal to the rate using stool samples (30/30, 100%), whereas the detection rate in FS was significantly lower (25/30, 83.2%; p=0.019). Sensitivity of FS for detection of C. difficile by PCR, TC, GDH and toxin A/B EIA was 83.3%, 85.7%, 88% and 68.9%, respectively. Storage of swabs at -80°C had no impact on the detection rate.

Conclusion: FS cannot replace stool samples in the two-step laboratory diagnosis of CDI as sensitivities were too low, probably due to diluting effects of the fecal sample in the liquid medium. For simple PCR-based detection of C. difficile dry swabs proved to be a suitable alternative to the use of stool samples.