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

Abstract

For the diagnosis of infection (CDI), microbiological testing is almost always accomplished through the analysis of stool specimens. We evaluated the performances of rectal swabs with liquid transport medium (FS) and nylon flocked dry swabs for the detection of Additionally, the impact on the diagnostic yield of storing swabs at -80°C for up to 3 months was evaluated. Sixty clinical stool samples positive for by PCR were used for simulating rectal swabbing. FS and dry swabs were dipped into the stool and tested by PCR directly after swabbing at 1 and 3 months 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 enzyme immunoassay (EIA), as well as by toxigenic culture (TC). Using dry swabs, the PCR-based detection rate of was equal to the rate using stool samples (30/30 [100%]), whereas the detection rate in FS was significantly lower (25/30 [83.2%]; = 0.019). The sensitivities of FS for detecting by PCR, TC, GDH testing, and toxin A/B EIA were 83.3%, 85.7%, 88%, and 68.9%, respectively. Storage of swabs at -80°C had no impact on the detection rate. FS cannot replace stool samples in the two-step laboratory diagnosis of CDI, as the sensitivities were too low, probably due to diluting effects of the fecal sample in the liquid medium. For simple PCR-based detection of , dry swabs proved to be a suitable alternative to the use of stool samples.

Evidence of transmission of Clostridium difficile in asymptomatic patients following admission screening in a tertiary care hospital

“…These figures likely underestimate the true rates of asymptomatic carriage as our swab based screening method is likely less sensitive than stool cultures, as was evident by the fact that we did not detect active CDI in five individuals[33]. Although studies have suggested that dry fecal swabs have comparable sensitivity to swabs dipped in stool for CD detection[34], these studies have all been performed in active CDI cases and not when assessing CD colonization, which would likely have a lower concentration of CD compared to active CDI cases. In addition, a significant proportion of participants in our study (37%) had only one swab collected and since CD shedding in the majority of asymptomatic carriers was picked up intermittently, we likely underestimate the proportion of asymptomatic carriage in our cohort.…”

Incidence and predictive biomarkers of Clostridioides difficile infection in hospitalized patients receiving broad-spectrum antibiotics

“…The low observed carriage prevalence may be due to a potentially lower sensitivity of rectal swabs compared to stool samples for detection of toxigenic C. difficile carriage. PCR testing based on swabs dipped in stool samples of CDI patients has yielded high detection rates, but this may be different for detection of colonization 22 . On the other hand, the relative risk of toxigenic C. difficile carriage for CDI is high compared to previous studies in which relative risks between 2.5 and 10 have been observed 11 .…”

Rectal Swabs as an Alternative Sample Collection Method to Bulk Stool for the Real-Time PCR Detection of Giardia duodenalis

“…In a study targeting C. difficile, qPCR detection by dry flocked swabs versus bulk stool was 100% concordant, whereas flocked swabs stored in liquid transport medium had significantly lower sensitivity. 43 However, the referenced study simulated swab collection by dipping swabs in bulk stool samples.…”