Performance of the artus C. difficile QS-RGQ Kit for the detection of toxigenic Clostridium difficile

https://doi.org/10.1016/j.clinbiochem.2016.08.013Get rights and content

Highlights

  • The performance of the artus C. difficile is excellent compared with TC.

  • The performance of the artus C. difficile is comparable to that of the Xpert C. difficile.

  • Both PCR assays could be useful diagnostic options in clinical laboratories.

Abstract

Objectives

Nucleic acid amplification tests are commonly used for the direct detection of toxigenic Clostridium difficile. We evaluated the diagnostic performance of newly launched, artus C. difficile QS-RGQ Kit (artus C. difficile, QIAGEN, Hilden, Germany), in comparison with toxigenic culture (TC) and Xpert C. difficile (Cepheid, Sunnyvale, CA, USA).

Design and methods

In prospectively collected 261 diarrheal specimens, the artus C. difficile and the Xpert C. difficile assays were performed. TC using chromogenic agar (chromID CD agar, bioMérieux, Marcy-l'Etoile, France) was used a reference method.

Results

Based on TC, the sensitivity and specificity of the artus C. difficile were 98.2% and 93.6%, respectively, and those of the Xpert C. difficile were 94.6% and 94.6%, respectively; there was no statistical difference. The agreement between the artus C. difficile and the Xpert C. difficile was almost perfect (kappa = 0.918). In the artus C. difficile, the cycle threshold (Ct) values of tcdA were constantly lower than those of tcdB in all positive specimens (mean Ct, 24.5 vs. 26.4; mean difference of 1.9). Three specimens were considered tcdA +/tcdB- by the difference of Ct cutoffs between tcdA and tcdB (38.3 and 36.5, respectively).

Conclusions

The performance of the artus C. difficile is excellent compared with TC and is comparable to that of the Xpert C. difficile. Both PCR assays could be useful diagnostic options for the direct detection of toxigenic C. difficile in clinical laboratories. The optimal Ct cutoff of tcdA and tcdB for artus C. difficile may be further validated in following studies.

Introduction

Clostridium difficile is the most common cause of healthcare-associated diarrhea, and toxigenic C. difficile infection (CDI) accounts for 15% to 25% of all antibiotic-associated diarrheas [1], [2]. CDI has become prevalent and less responsive to treatment worldwide [3], [4]. CDI is associated with considerable morbidity and mortality, which increase healthcare costs [5]. Accordingly, accurate and rapid diagnosis of CDI is essential for proper treatment, infection control, and reduction of healthcare costs.

The diagnosis of CDI is based on both clinical and laboratory findings [2]. The laboratory gold standard for detecting C. difficile is the toxigenic culture (TC); anaerobic culture is followed by confirmation of toxin production by enzyme immunoassay, cell culture cytotoxin neutralization test, or DNA amplification assay [2], [3]. However, TC has limitations such as a long turnaround time and technical complexities [6]. Recently, many laboratories have implemented nucleic acid amplification testing (NAAT) for the direct detection of toxigenic C. difficile. NAAT is highly sensitive and specific and could be used as a stand-alone test although there are some concerns on its single use [7], [8], [9], [10].

The artus C. difficile QS-RGQ Kit (artus C. difficile, QIAGEN, Hilden, Germany) is a newly launched, real-time PCR assay for the detection of toxin A (tcdA) and toxin B (tcdB) genes, and it was evaluated in only one study from Germany [11]. In this study, the diagnostic performance of the artus C. difficile was compared with that of the Xpert C. difficile (Cepheid, Sunnyvale, CA, USA), which was also recently introduced and well-validated [12], [13], [14], [15]. TC was used as a gold standard to compare the performances of both assays.

Section snippets

Clinical specimens

This in vitro study using remnant stool specimens was approved by the Institutional Review Board of the Konkuk University Medical Center, Seoul, Korea (a tertiary referral hospital with 900 beds). From May to September 2015, a total of 261 loose stool specimens were prospectively collected; these specimens were submitted to the clinical microbiology laboratory for C. difficile testing as a part of routine care. Duplicate specimens from the same patients or specimens with insufficient amount

Results

From the 261 stool specimens, two specimens showed invalid results by the artus C. difficile and one specimen by the Xpert C. difficile. These specimens showed no growth of toxin-producing C. difficile by TC. Excluding these three specimens, 258 specimens were analyzed for performance evaluation. Among 258 specimens, 55 (21.3%) were positive for growth of toxin-producing C. difficile by TC. Sixty seven (26.0%) specimens were positive for the artus C. difficile and 63 (24.4%) for the Xpert C.

Discussion

In this study, we compared the diagnostic performance of the artus C. difficile with that of the Xpert C. difficile, which showed excellent sensitivities (94.4%–100.0%) and specificities (93.0%–98.8%) in previous studies [11], [12], [13], [14], [15], [19]. The performance of the artus C. difficile was comparable to that of the Xpert C. difficile, and the agreement between the artus C. difficile and the Xpert C. difficile was almost perfect (kappa = 0.918). Based on TC, the sensitivity and

Conflict of interest

The authors have no conflict of interest related to this article.

Author contribution

Moon H analyzed the data and wrote the draft; Kim HN and Kim JY collected the specimens and participated in the experiment; Hur M designed this study and finalized the draft; Kim H participated in the experiment; Yun YM reviewed the draft and commented on it.

Acknowledgements

This study was supported by Konkuk University.

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