Detection of Clostridioides difficile toxin B gene in clinical stool specimens using rapid diagnostic quenching probe-polymerase chain reaction assay

We tested the accuracy of quenching probe-polymerase chain reaction (QP-PCR) for detecting Clostridioides difficile toxin B gene (tcdB) in stools from inpatients with suspected C. difficile infection and compared the results with other nucleic acid amplification tests (NAATs). Toxigenic culture results were used as reference for comparison. QP-PCR had comparable diagnostic accuracy with other NAATs and prior bead-beating enabled detection of tcdB in specimens judged as negative, without bead-beating. Taken together, the QP-PCR either with or without bead-beating showed sufficient effectiveness for detecting tcdB in stool specimens.

Three different patterns of positive Clostridium difficile laboratory tests. A comparison of clinical behavior

Clostridium difficile (CD) diagnosis is very varied and under discussion. Different research groups disagree on the clinical significance of patients with negative direct toxin and positive polymerase chain reaction (PCR) or even more with direct toxin and glutamate dehydrogenase (GDH) both negatives, but CD detected by toxigenic culture (TC). The objective was to analyze the characteristics of patients with 3 different diagnostic criteria. We compared these 3 groups of patients: group 1: (GDH+/direct toxin+/PCR+), group 2: (GDH+/direct toxin-/PCR+) and group 3: (GDH-/direct toxin-/PCR not done/TC+). The proportion of patients with CD infection (CDI) (not colonization) for groups 1 to 3 was, respectively, 90.3%, 95.4%, and 59.1%. No differences between severity (40.8%, 38.5%, 27.3%), recurrence (20.3%, 24.1%, 7.6%), or related mortality (12.5%, 5.2%, 0%) were found within the 3 groups of patients. Laboratory clinical results should not be used as the only tool to differentiate CDI versus colonization or severity. We recommend that PCR or a second-look TC be performed on all patients.

Evaluation of a nucleic acid amplification assay for the diagnosis of Clostridioides difficile infection

Clostridioides difficile is the leading cause of healthcare-associated diarrhea and the laboratory diagnosis of Clostridioides difficile infection (CDI) continues to be challenging. Accurate and rapid identification of C. difficile will reduce unnecessary antibiotic use and ensure contact isolation to control the spread of CDI. In this study, diagnostic performance of BD MAX Cdiff assay (Becton Dickinson, USA) was evaluated for the detection of C. difficile in 2502 fresh stool samples from hospitalized children and adult patients and the results were compared to toxigenic culture. The frequency of CDI in adults and pediatric patients were found as 3.3% and 6.2%, respectively. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of BD MAX Cdiff assay were found as; 100%, 99.7%, 93%, and 100% for all patients; 100%, 99.7%, 96.2%, and 100% for pediatric patients; and 100%, 99.6%, 90.2%, and 100% for adult patients, respectively. We concluded that BD MAX Cdiff assay with high sensitivity, specificity, and PPV is useful for the diagnosis of CDI. With a high NPV of 100%, BD MAX Cdiff assay is also suitable for the exclusion of CDI.

Diagnosis of Clostridium difficile infection by toxigenic culture and PCR assay

BACKGROUND AND OBJECTIVES

Clostridium difficile is responsible for 15-25% of nosocomial antibiotic associated diarrhea (AAD) cases and all cases of pseudomembranous colitis. C. difficile has two major virulence factors, toxin A (enterotoxin) and toxin B (cytotoxin). The aim of this study was to determine the frequency of C. difficile strains in patients with diarrhea in Babol' hospitals with toxigenic culture and PCR assay.

MATERIALS AND METHODS

One hundred stool specimens were taken from diarrheal patients in hospitals of the city of Babol. All patients had a history of antibiotic use. The samples were cultured on CCFA medium. In the next stage, toxigenic culture was performed for isolated C. difficile strains. Then, PCR assay was used to identify gdh, tcdA and tcdB genes among isolated C. difficile strains.

RESULTS

From the 100 stool samples, eight (8%) samples were positive in C. difficile culture. In toxigenic culture, two (2%) of these strains had cytopathic effects on Vero cells. All eight strains had the gdh gene. This gene is specific for C. difficile. Two strains that had cytopathic effects on toxigenic culture were positive for toxin genes.

CONCLUSION

The frequency of toxigenic strains in different parts of the world is variable, and needs to be continually investigated. In the present study, the PCR method had a good correlation with toxigenic culture. Thus, it can replace the laborious and costly cell culture method.

Trends in the use of laboratory tests for the diagnosis of Clostridium difficile infection and association with incidence rates in Quebec, Canada, 2010-2014

BACKGROUND

Several Clostridium difficile infection (CDI) surveillance programs do not specify laboratory strategies to use. We investigated the evolution in testing strategies used across Quebec, Canada, and its association with incidence rates.

METHODS

Cross-sectional study of 95 hospitals by surveys conducted in 2010 and in 2013-2014. The association between testing strategies and institutional CDI incidence rates was analyzed via multivariate Poisson regressions.

RESULTS

The most common assays in 2014 were toxin A/B enzyme immunoassays (EIAs) (61 institutions, 64%), glutamate dehydrogenase (GDH) EIAs (51 institutions, 53.7%), and nucleic acid amplification tests (NAATs) (34 institutions, 35.8%). The most frequent algorithm was a single-step NAAT (20 institutions, 21%). Between 2010 and 2014, 35 institutions (37%) modified their algorithm. Institutions detecting toxigenic C difficile instead of C difficile toxin increased from 14 to 37 (P < .001). Institutions detecting toxigenic C difficile had higher CDI rates (7.9 vs 6.6 per 10,000 patient days; P = .01). Institutions using single-step NAATs, GDH plus toxigenic cultures, and GDH plus cytotoxicity assays had higher CDI rates than those using an EIA-based algorithm (P < .05).

CONCLUSIONS

Laboratory detection of CDI has changed since 2010. There is an association between diagnostic algorithms and CDI incidence. Mitigation strategies are warranted.

Current knowledge on the laboratory diagnosis of Clostridium difficile infection

Clostridium difficile (C. difficile) is a spore-forming, toxin-producing, gram-positive anaerobic bacterium that is the principal etiologic agent of antibiotic-associated diarrhea. Infection with C. difficile (CDI) is characterized by diarrhea in clinical syndromes that vary from self-limited to mild or severe. Since its initial recognition as the causative agent of pseudomembranous colitis, C. difficile has spread around the world. CDI is one of the most common healthcare-associated infections and a significant cause of morbidity and mortality among older adult hospitalized patients. Due to extensive antibiotic usage, the number of CDIs has increased. Diagnosis of CDI is often difficult and has a substantial impact on the management of patients with the disease, mainly with regards to antibiotic management. The diagnosis of CDI is primarily based on the clinical signs and symptoms and is only confirmed by laboratory testing. Despite the high burden of CDI and the increasing interest in the disease, episodes of CDI are often misdiagnosed. The reasons for misdiagnosis are the lack of clinical suspicion or the use of inappropriate tests. The proper diagnosis of CDI reduces transmission, prevents inadequate or unnecessary treatments, and assures best antibiotic treatment. We review the options for the laboratory diagnosis of CDI within the settings of the most accepted guidelines for CDI diagnosis, treatment, and prevention of CDI.

C. difficile PCR-ribotype 023 might go undetected when using ChromId C. difficile agar

We compared the performance of the new chromogenic medium ChromID C. difficile with that of CLO agar. ChromID C. difficile agar is a sensitive medium that can accelerate the presumptive identification of C. difficile, however ribotype 023 might go undetected when using this chromogenic medium.

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

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.

Performance of chromID Clostridium difficile agar compared with BBL C. difficile selective agar for detection of C. difficile in stool specimens

We evaluated the performance of a new chromogenic medium for detection of Clostridium difficile, chromID C. difficile agar (CDIF; bioMérieux, France), by comparison with BBL C. difficile Selective Agar (CDSA; Becton Dickinson and Company, USA). After heat pre-treatment (80℃, 5 min), 185 diarrheal stool samples were inoculated onto the two media types and incubated anaerobically for 24 hr and 48 hr for CDIF and for 48 hr and 72 hr for CDSA. All typical colonies on each medium were examined by Gram staining, and the gram-positive rods confirmed to contain the tpi gene by PCR were identified as C. difficile. C. difficile was recovered from 36 samples by using a combination of the two media. The sensitivity with CDIF 48 hr was highest (100%) and was significantly higher than that with CDIF 24 hr (58.3%; P<0.001), because samples with a low burden of C. difficile tended to require prolonged incubation up to 48 hr (P<0.001). The specificity of CDIF 24 hr and CDIF 48 hr (99.3% and 90.6%, respectively) was significantly higher than that of CDSA 48 hr and CDSA 72 hr (72.5% and 67.1%, respectively; P<0.001). CDIF was effective for detecting C. difficile in heat-pretreated stool specimens, thus reducing unnecessary testing for toxin production in non-C. difficile isolates and turnaround time.