What is the current role of algorithmic approaches for diagnosis of Clostridium difficile infection? J Clin Microbiol. 2010;48:4347-4353. [PMID: 20980568 DOI: 10.1128/jcm.02028-10]

Laboratory diagnosis of Clostridioides difficile infection in symptomatic patients: what can we do better?

The laboratory diagnosis of Clostridioides difficile infection (CDI) is challenging since this bacteria may be detected in healthy people and toxin production detection is not sensitive enough to be used alone. Thus, there is no single test with adequate sensitivity and specificity to be used in laboratory diagnosis. We evaluated the performance of tests used in the diagnosis of CDI in symptomatic patients with risk factors in hospitals in southern Brazil. Enzyme immunoassays (EIA) for glutamate dehydrogenase antigen (GDH) and toxins A/B, real-time polymerase chain reaction (qPCR), GeneXpert system, and a two-step algorithm comprising GDH/TOXIN EIA performed simultaneously followed by GeneXpert for outliers were evaluated. Toxigenic strain in stool culture was considered CDI positive (gold standard). Among 400 samples tested, 54 (13.5%) were positive for CDI and 346 (86.5%) were negative. The diagnosis of the two-step algorithm and qPCR had an excellent performance with an accuracy of 94.5% and 94.2%, respectively. The Youden index showed that GeneXpert as a single test (83.5%) and the two-step algorithm (82.8%) were the most effective assays. Diagnosing CDI and non-CDI diarrhea could be successfully attained by the combination of clinical data with accuracy of laboratory tests.

A cost of illness comparison for toxigenic Clostridioides difficile diagnosis algorithms in developing countries

BACKGROUND

Availability of several commercial tests with different Clostridioides difficile targets contributes to uncertainty and controversies around the optimal diagnostic algorithm. While numerous studies have estimated the financial impact of C. difficile infection, models to guide testing strategies decisions in developing countries, where economic value significantly impacts clinical practice, are currently not available.

AIM

To determine the cost of illness of different C. difficile infection (CDI) diagnostic strategies in developing countries.

METHODS

Cost-comparison analysis was performed to compare eleven different algorithms of CDI diagnosis. The basis of calculation was a hypothetical cohort of 1000 adult inpatients suspected of CDI. We analyzed turnaround time of test results (i.e., time from taking sample to results emission), test performance (i.e., sensitivity and specificity) and testing costs. Patients were divided in true positive, false positive, true negative and false negative in order to integrate test performance and economics effects. Additional medical costs were calculated: costs of hygiene, medication, length of stay and intensive care unit costs, based on a Brazilian University Hospital costs. CDI prevalence was considered 22.64%.

FINDINGS

From laboratory-assisted tests, simultaneous glutamate dehydrogenase (GDH) and toxin A/B rapid immunoassay arbitrated by nucleic acid amplification test (NAAT) presented the lowest cost of illness (450,038.70 USD), whereas standalone NAAT had the highest (523,709.55 USD). Empirical diagnosis only presented the highest overall cost (809,605.44 USD).

CONCLUSION

The two-step algorithm with simultaneous GDH and toxin A/B rapid immunoassay arbitrated by NAAT seems to be the best strategy for CDI diagnosis in developing countries.

Recommendations for the diagnosis and treatment of Clostridioides difficile infection: An official clinical practice guideline of the Spanish Society of Chemotherapy (SEQ), Spanish Society of Internal Medicine (SEMI) and the working group of Postoperative Infection of the Spanish Society of Anesthesia and Reanimation (SEDAR)

This document gathers the opinion of a multidisciplinary forum of experts on different aspects of the diagnosis and treatment of Clostridioides difficile infection (CDI) in Spain. It has been structured around a series of questions that the attendees considered relevant and in which a consensus opinion was reached. The main messages were as follows: CDI should be suspected in patients older than 2 years of age in the presence of diarrhea, paralytic ileus and unexplained leukocytosis, even in the absence of classical risk factors. With a few exceptions, a single stool sample is sufficient for diagnosis, which can be sent to the laboratory with or without transportation media for enteropathogenic bacteria. In the absence of diarrhoea, rectal swabs may be valid. The microbiology laboratory should include C. difficile among the pathogens routinely searched in patients with diarrhoea. Laboratory tests in different order and sequence schemes include GDH detection, presence of toxins, molecular tests and toxigenic culture. Immediate determination of sensitivity to drugs such as vancomycin, metronidazole or fidaxomycin is not required. The evolution of toxin persistence is not a suitable test for follow up. Laboratory diagnosis of CDI should be rapid and results reported and interpreted to clinicians immediately. In addition to the basic support of all diarrheic episodes, CDI treatment requires the suppression of antiperistaltic agents, proton pump inhibitors and antibiotics, where possible. Oral vancomycin and fidaxomycin are the antibacterials of choice in treatment, intravenous metronidazole being restricted for patients in whom the presence of the above drugs in the intestinal lumen cannot be assured. Fecal material transplantation is the treatment of choice for patients with multiple recurrences but uncertainties persist regarding its standardization and safety. Bezlotoxumab is a monoclonal antibody to C. difficile toxin B that should be administered to patients at high risk of recurrence. Surgery is becoming less and less necessary and prevention with vaccines is under research. Probiotics have so far not been shown to be therapeutically or preventively effective. The therapeutic strategy should be based, rather than on the number of episodes, on the severity of the episodes and on their potential to recur. Some data point to the efficacy of oral vancomycin prophylaxis in patients who reccur CDI when systemic antibiotics are required again.

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.

A Multicenter Study of the Revogene C. difficile System for Detection of the Toxin B Gene from Unformed Stool Specimens

Clostridioides difficile is the leading cause of diarrhea in hospitalized U.S. patients and results in over 400,000 cases of C. difficile infection per year. C. difficile infections have mortality rates of 6 to 30% and significantly increase health care costs, because of increased length of stay and increased frequency of readmissions due to recurrences. Efforts to reduce the spread of C. difficile in hospitals have led to the development of rapid sensitive diagnostic methods. A multicenter study was performed to establish the performance characteristics of the Revogene C. difficile test (Meridian Bioscience, Cincinnati, OH, USA) for use in detection of the toxin B (tcdB) gene from toxigenic C. difficile The Revogene instrument is a new molecular platform that uses real-time PCR to detect nucleic acids in up to 8 specimens at a time. A total of 2,461 specimens from symptomatic patients that had been submitted for C. difficile testing were enrolled at 7 sites throughout the United States and Canada for evaluation of the assay. Each stool specimen was tested for the presence of the tcdB gene using the Revogene C. difficile test, and results were compared with those of the reference method, a combination of direct and enriched culture methods. Overall, the Revogene C. difficile test demonstrated a sensitivity of 85.0% (95% confidence interval, 80% to 88%) and a specificity of 97.2% (95% confidence interval, 96% to 98%). The Revogene C. difficile test, using clinical stool specimens for detection of tcdB in C. difficile, demonstrated acceptable sensitivity and specificity, with a short turnaround time.

Analysis of Routine and Integrative Data from Clostridioides difficile Infection Diagnosis and the Consequent Observations

Background:

Clostridioides difficileInfection (CDI) is an acute disease that needs a fast proper treatment. Unfortunately, the diagnosis, and above all the understanding of the results, remain arduous.

Objective:

This study analyzed routine and integrative results of all fecal samples from patients over time. Our aim was to understand the dynamics of CDI infection and the meaning of “difficult to interpret” results, to make physicians better understand the various tools they can use.

Methods:

We evaluated routine results obtained from 815 diarrheal stools with Enzyme Immunoassay (EIA) that detectsC. difficileGlutamate Dehydrogenase (GDH) antigen and toxin B. We also reanalyzed a part of samples using integrative tests: a Real-time polymerase chain reaction (RT-PCR) forC. difficiletoxin B gene (tcdB) and the automated immunoassay VIDASC. difficilesystem for GDH and toxins A/B.

Results:

EIA GDH positivity increased through multiple testing over time, with aPvalue <0.001, depicting a sort of bacterial growth curve. Eighty-five percent of GDH positive/toxin B negative,i.e., discrepant, samples PCR weretcdBpositive, 61.5% of discrepanttcdBpositive samples were VIDAS toxins A/B positive, and 44.4% of GDH EIA negative stools were VIDAS GDH positive.

Conclusion:

The results confirmed the low sensitivity of the EIA system forC. difficileGDH and toxins, questioned the use of the latter for concluding any CDI diagnostic algorithm, and led us to indicate the algorithm beginning with tcdB molecular research, and continuing in positive cases with VIDAS CD GDH method, as the most effective for CDI.

Implementation of a Clostridioides difficile prevention bundle: Understanding common, unique, and conflicting work system barriers and facilitators for subprocess design

OBJECTIVE

Clostridioides difficile (C. difficile) poses a major challenge to the healthcare system. We assessed factors that should be considered when designing subprocesses of a C. difficile infection (CDI) prevention bundle.

DESIGN

Phenomenological qualitative study.

METHODS

We conducted 3 focus groups of environmental services (EVS) staff, physicians, and nurses to assess their perspectives on a CDI prevention bundle. We used the Systems Engineering Initiative for Patient Safety (SEIPS) model to examine 5 subprocesses of the CDI bundle: diagnostic testing, empiric isolation, contact isolation, hand hygiene, and environmental disinfection. We coded transcripts to the 5 SEIPS elements and ensured scientific rigor. We sought to determine common, unique, and conflicting factors across stakeholder groups and subprocesses of the CDI bundle.

RESULTS

Each focus group lasted 1.5 hours on average. Common work-system barriers included inconsistencies in knowledge and practice of CDI management procedures; increased workload; poor setup of aspects of the physical environment (eg, inconvenient location of sinks); and inconsistencies in CDI documentation. Unique barriers and facilitators were related to specific activities performed by the stakeholder group. For instance, algorithmic approaches used by physicians facilitated timely diagnosis of CDI. Conflicting barriers or facilitators were related to opposing objectives; for example, clinicians needed rapid placement of a patient in a room while EVS staff needed time to disinfect the room.

CONCLUSIONS

A systems engineering approach can help to holistically identify factors that influence successful implementation of subprocesses of infection prevention bundles.

Clostridioides difficile Infection in the Stem Cell Transplant and Hematologic Malignancy Population

Clostridioides difficile infection (CDI) is common in the stem cell transplant (SCT) and hematologic malignancy (HM) population and mostly occurs in the early posttransplant period. Treatment of CDI in SCT/HM is the same as for the general population, with the exception that fecal microbiota transplant (FMT) has not been widely adopted because of safety concerns. Several case reports, small series, and retrospective studies have shown that FMT is effective and safe. A randomized controlled trial of FMT for prophylaxis of CDI in SCT patients is underway. In addition, an abundance of novel therapeutics for CDI is currently in development.

Can a toxin gene NAAT be used to predict toxin EIA and the severity of Clostridium difficile infection?

Background

Diagnosis of C. difficile infection (CDI) is controversial because of the many laboratory methods available and their lack of ability to distinguish between carriage, mild or severe disease. Here we describe whether a low C. difficile toxin B nucleic acid amplification test (NAAT) cycle threshold (CT) can predict toxin EIA, CDI severity and mortality.

Methods

A three-stage algorithm was employed for CDI testing, comprising a screening test for glutamate dehydrogenase (GDH), followed by a NAAT, then a toxin enzyme immunoassay (EIA). All diarrhoeal samples positive for GDH and NAAT between 2012 and 2016 were analysed. The performance of the NAAT CT value as a classifier of toxin EIA outcome was analysed using a ROC curve; patient mortality was compared to CTs and toxin EIA via linear regression models.

Results

A CT value ≤26 was associated with ≥72% toxin EIA positivity; applying a logistic regression model we demonstrated an association between low CT values and toxin EIA positivity. A CT value of ≤26 was significantly associated (p = 0.0262) with increased one month mortality, severe cases of CDI or failure of first line treatment. The ROC curve probabilities demonstrated a CT cut off value of 26.6.

Discussions

Here we demonstrate that a CT ≤26 indicates more severe CDI and is associated with higher mortality. Samples with a low CT value are often toxin EIA positive, questioning the need for this additional EIA test.

Conclusions

A CT ≤26 could be used to assess the potential for severity of CDI and guide patient treatment.

Toxin positivity and tcdB gene load in broad-spectrum Clostridium difficile infection

PURPOSE

This study aimed to evaluate the clinical significance of toxin positivity and toxin gene load, and the relation between them in the broad spectrum of Clostridium difficile infection (CDI) including colonization, significant diarrhea, and severe disease.

METHODS

We included 2671 fecal samples submitted for CDI diagnosis and 180 samples from healthy individuals. The clinical spectrum was categorized as category I (toxigenic C. difficile positive without clinical CDI criteria), category II (mild CDI), and category III (severe CDI). Clinical parameters were compared based on toxin EIA and tcdB C _t values. C _t values of tcdB PCR for predicting toxin EIA positivity were assessed using receiver-operating characteristic (ROC) curves.

RESULTS

The median C _t values of tcdB PCR and toxin positivity were not significantly correlated with clinical spectrum of CDI (27.5, 28.2, and 26.1 for tcdB C _t and 55.0, 56.6, and 60.9% for toxin EIA positivity in category I, II, and III, respectively, P > 0.05). There were significant differences in the tcdB C _t values between toxin EIA-positive and -negative groups (P < 0.001). Optimal cutoff for the tcdB C _t value for estimating toxin EIA positivity was 26.3 with 79.3% sensitivity and 83.6% specificity with good area under the curves (AUC, 0.848).

CONCLUSIONS

The C _t values successfully predicted toxin EIA positivity and could be used as a surrogate for toxin EIA positivity in the diagnostic algorithm and routine analysis. Further studies are needed to validate the clinical significance of tcdB PCR C _t value in toxigenic C. difficile colonization and infection.

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.

Diagnosis and outcome of Clostridium difficile infection by toxin enzyme immunoassay and polymerase chain reaction in an island population

BACKGROUND AND AIM

Clostridium difficile infection (CDI) is a potentially life-threatening cause of diarrhea. Correct laboratory diagnosis is essential to differentiate CDI from other causes of diarrhea. A positive fecal C. difficile toxin (CDT) is the best indicator of CDI, but the significance of a positive fecal nucleic acid amplification test (NAAT) remains unclear. Our aim was to elucidate the significance of CDI diagnostics in patients in Jersey.

METHODS

A retrospective, 5-year study was conducted at an island district general hospital of patients who developed CDI. Patients were grouped according to CDT and NAAT status and their association with outcome (indicators of severity and 30-day case-fatality rate) compared.

RESULTS

A total of 207 specimens were toxin positive, 92 NAAT positive and toxin negative, and 39 had a stool sample negative by both toxin and NAAT testing. A positive toxin stool sample was associated with both significantly higher white cell count (14.5 × 10⁹ /L vs 11.3 × 10⁹ /L, P = 0.003) and C-reactive protein (114.7 mg/dL vs 82.9 mg/dL, P = 0.001), but NAAT positivity was not (P = 0.269, 0.728). A positive CDT assay was a significant independent predictor of death (odds ratio [OR]: 1.89 [95% CI: 1.04-3.43], P = 0.046), but a positive NAAT in CDT negative samples was not (OR: 1.02 [95% CI: 0.34-3.12], P = 1.0).

CONCLUSIONS

The findings of this study, derived from evolving clinical practice, provide greater clarity in the interpretation of CDI diagnostics. In CDT-negative disease, a positive NAAT neither predicts disease severity nor mortality. NAAT-positive and toxin-negative patients require instigation of infection control measures, but the need for specific treatment remains unclear.

Effect of Fecal Microbiota Transplantation on Recurrence in Multiply Recurrent Clostridium difficile Infection: A Randomized Trial

BACKGROUND

To date, evidence for the efficacy of fecal microbiota transplantation (FMT) in recurrent Clostridium difficile infection (CDI) has been limited to case series and open-label clinical trials.

OBJECTIVE

To determine the efficacy and safety of FMT for treatment of recurrent CDI.

DESIGN

Randomized, controlled, double-blind clinical trial. (ClinicalTrials.gov: NCT01703494).

SETTING

Two academic medical centers.

PATIENTS

46 patients who had 3 or more recurrences of CDI and received a full course of vancomycin for their most recent acute episode.

INTERVENTION

Fecal microbiota transplantation with donor stool (heterologous) or patient's own stool (autologous) administered by colonoscopy.

MEASUREMENTS

The primary end point was resolution of diarrhea without the need for further anti-CDI therapy during the 8-week follow-up. Safety data were compared between treatment groups via review of adverse events (AEs), serious AEs (SAEs), and new medical conditions for 6 months after FMT. Fecal microbiota analyses were performed on patients' stool before and after FMT and also on donors' stool.

RESULTS

In the intention-to-treat analysis, 20 of 22 patients (90.9%) in the donor FMT group achieved clinical cure compared with 15 of 24 (62.5%) in the autologous FMT group (P = 0.042). Resolution after autologous FMT differed by site (9 of 10 vs. 6 of 14 [P = 0.033]). All 9 patients who developed recurrent CDI after autologous FMT were free of further CDI after subsequent donor FMT. There were no SAEs related to FMT. Donor FMT restored gut bacterial community diversity and composition to resemble that of healthy donors.

LIMITATION

The study included only patients who had 3 or more recurrences and excluded those who were immunocompromised and aged 75 years or older.

CONCLUSION

Donor stool administered via colonoscopy seemed safe and was more efficacious than autologous FMT in preventing further CDI episodes.

PRIMARY FUNDING SOURCE

National Institute of Diabetes and Digestive and Kidney Diseases.

Rapid detection of Clostridium difficile toxins and laboratory diagnosis of Clostridium difficile infections

BACKGROUND

Clostridium difficile is an anaerobic, spore-forming and Gram-positive bacillus. It is the major cause of antibiotic-associated diarrhea prevailing in hospital settings. The morbidity and mortality of C. difficile infection (CDI) has increased significantly due to the emergence of hypervirulent strains. Because of the poor clinical different between CDI and other causes of hospital-acquired diarrhea, laboratory test for C. difficile is an important intervention for diagnosis of CDI.

OBJECTIVE

Laboratory tests for CDI can broadly detect either the organisms or its toxins. Currently, several laboratory tests are used for diagnosis of CDI, including toxigenic culture, glutamate dehydrogenase detection, nucleic acid amplification testing, cell cytotoxicity assay, and enzyme immunoassay towards toxin A and/or B. This review focuses on the rapid testing of C. difficile toxins and currently available methods for diagnosis of CDI, giving an overview of the role that the toxins rapid detecting plays in clinical diagnosis of CDI.

Comparison of Diagnostic Algorithms for Detecting Toxigenic Clostridium difficile in Routine Practice at a Tertiary Referral Hospital in Korea

Since every single test has some limitations for detecting toxigenic Clostridium difficile, multistep algorithms are recommended. This study aimed to compare the current, representative diagnostic algorithms for detecting toxigenic C. difficile, using VIDAS C. difficile toxin A&B (toxin ELFA), VIDAS C. difficile GDH (GDH ELFA, bioMérieux, Marcy-l’Etoile, France), and Xpert C. difficile (Cepheid, Sunnyvale, California, USA). In 271 consecutive stool samples, toxigenic culture, toxin ELFA, GDH ELFA, and Xpert C. difficile were performed. We simulated two algorithms: screening by GDH ELFA and confirmation by Xpert C. difficile (GDH + Xpert) and combined algorithm of GDH ELFA, toxin ELFA, and Xpert C. difficile (GDH + Toxin + Xpert). The performance of each assay and algorithm was assessed. The agreement of Xpert C. difficile and two algorithms (GDH + Xpert and GDH+ Toxin + Xpert) with toxigenic culture were strong (Kappa, 0.848, 0.857, and 0.868, respectively). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of algorithms (GDH + Xpert and GDH + Toxin + Xpert) were 96.7%, 95.8%, 85.0%, 98.1%, and 94.5%, 95.8%, 82.3%, 98.5%, respectively. There were no significant differences between Xpert C. difficile and two algorithms in sensitivity, specificity, PPV and NPV. The performances of both algorithms for detecting toxigenic C. difficile were comparable to that of Xpert C. difficile. Either algorithm would be useful in clinical laboratories and can be optimized in the diagnostic workflow of C. difficile depending on costs, test volume, and clinical needs.

Selected Topics in Anaerobic Bacteriology

Alteration in the host microbiome at skin and mucosal surfaces plays a role in the function of the immune system, and may predispose immunocompromised patients to infection. Because obligate anaerobes are the predominant type of bacteria present in humans at skin and mucosal surfaces, immunocompromised patients are at increased risk for serious invasive infection due to anaerobes. Laboratory approaches to the diagnosis of anaerobe infections that occur due to pyogenic, polymicrobial, or toxin-producing organisms are described. The clinical interpretation and limitations of anaerobe recovery from specimens, anaerobe-identification procedures, and antibiotic-susceptibility testing are outlined. Bacteriotherapy following analysis of disruption of the host microbiome has been effective for treatment of refractory or recurrent Clostridium difficile infection, and may become feasible for other conditions in the future.

Controversies Around Epidemiology, Diagnosis and Treatment of Clostridium difficile Infection

Clostridium difficile infection is a major public health problem. However, in recent years the epidemiology, risk factors, diagnosis, and treatment of C. difficile infection have undergone a significant change. The incidence of C. difficile has increased, not only in the healthcare sector but also in the community. Hospital-acquired infection and community-acquired disease have different risk factors, with the latter occurring in children and younger individuals without a history of antibiotic use or previous infections. From a clinician's perspective, a quick efficient diagnosis is required for patient treatment; however, the old method of using enzyme immunoassays is insensitive and not very specific. Recent literature around diagnostic testing for C. difficile infection suggests using PCR or a two-step algorithm to improve sensitivity and specificity. More failures and recurrence with metronidazole have led to treatment algorithms suggesting its use for mild infections and switching to vancomycin if there is no clinical improvement. Alternatively, if signs and symptoms suggest severe infection, then oral vancomycin is recommended as a first-line agent. The addition of a new but costly agent, fidaxomicin, has seen some disparity between the European and North American guidelines with regard to when it should be used. Lastly, rapid developments and good results with fecal microbial transplantation have also left clinicians wondering about its place in therapy. This article reviews the literature around some of the recent controversies in the field of C. difficile infection.

Ultrasensitive Detection and Quantification of Toxins for Optimized Diagnosis of Clostridium difficile Infection

Recently developed ultrasensitive and quantitative methods for detection of Clostridium difficile toxins provide new tools for diagnosis and, potentially, for management of C. difficile infection (CDI). Compared to methods that detect toxigenic organism, ultrasensitive toxin detection may allow diagnosis of CDI with increased clinical specificity, without sacrificing clinical sensitivity; measurement of toxin levels may also provide information relevant to disease prognosis. This minireview provides an overview of these new toxin detection technologies and considers what these new tools might add to the field.

Overdiagnosis of Clostridium difficile Infection in the Molecular Test Era

IMPORTANCE

Clostridium difficile is a major cause of health care-associated infection, but disagreement between diagnostic tests is an ongoing barrier to clinical decision making and public health reporting. Molecular tests are increasingly used to diagnose C difficile infection (CDI), but many molecular test-positive patients lack toxins that historically defined disease, making it unclear if they need treatment.

OBJECTIVE

To determine the natural history and need for treatment of patients who are toxin immunoassay negative and polymerase chain reaction (PCR) positive (Tox-/PCR+) for CDI.

DESIGN, SETTING, AND PARTICIPANTS

Prospective observational cohort study at a single academic medical center among 1416 hospitalized adults tested for C difficile toxins 72 hours or longer after admission between December 1, 2010, and October 20, 2012. The analysis was conducted in stages with revisions from April 27, 2013, to January 13, 2015.

MAIN OUTCOMES AND MEASURES

Patients undergoing C difficile testing were grouped by US Food and Drug Administration-approved toxin and PCR tests as Tox+/PCR+, Tox-/PCR+, or Tox-/PCR-. Toxin results were reported clinically. Polymerase chain reaction results were not reported. The main study outcomes were duration of diarrhea during up to 14 days of treatment, rate of CDI-related complications (ie, colectomy, megacolon, or intensive care unit care) and CDI-related death within 30 days.

RESULTS

Twenty-one percent (293 of 1416) of hospitalized adults tested for C difficile were positive by PCR, but 44.7% (131 of 293) had toxins detected by the clinical toxin test. At baseline, Tox-/PCR+ patients had lower C difficile bacterial load and less antibiotic exposure, fecal inflammation, and diarrhea than Tox+/PCR+ patients (P < .001 for all). The median duration of diarrhea was shorter in Tox-/PCR+ patients (2 days; interquartile range, 1-4 days) than in Tox+/PCR+ patients (3 days; interquartile range, 1-6 days) (P = .003) and was similar to that in Tox-/PCR- patients (2 days; interquartile range, 1-3 days), despite minimal empirical treatment of Tox-/PCR+ patients. No CDI-related complications occurred in Tox-/PCR+ patients vs 10 complications in Tox+/PCR+ patients (0% vs 7.6%, P < .001). One Tox-/PCR+ patient had recurrent CDI as a contributing factor to death within 30 days vs 11 CDI-related deaths in Tox+/PCR+ patients (0.6% vs 8.4%, P = .001).

CONCLUSIONS AND RELEVANCE

Among hospitalized adults with suspected CDI, virtually all CDI-related complications and deaths occurred in patients with positive toxin immunoassay test results. Patients with a positive molecular test result and a negative toxin immunoassay test result had outcomes that were comparable to patients without C difficile by either method. Exclusive reliance on molecular tests for CDI diagnosis without tests for toxins or host response is likely to result in overdiagnosis, overtreatment, and increased health care costs.

Serum 25-Hydroxyvitamin D Levels are not Associated with Adverse Outcomes in Clostridium Difficile Infection

Clostridium difficile infection (CDI) is a significant source of healthcare-associated morbidity and mortality. This study investigated whether serum 25-hydroxyvitamin D is associated with adverse outcomes from CDI. Patients with CDI were prospectively enrolled. Charts were reviewed and serum 25-hydroxyvitamin D was measured. The primary outcome was a composite definition of severe disease: fever (temperature >38°C), acute organ dysfunction, or serum white blood cell count >15,000 cells/µL within 24-48 hours of diagnosis; lack of response to therapy by day 5; and intensive care unit admission; colectomy; or death within 30 days. Sixty-seven patients were included in the final analysis. Mean (±SD) serum 25-hydroxyvitamin D was 26.1 (±18.54) ng/mL. Severe disease, which occurred in 26 (39%) participants, was not associated with serum 25-hydroxyvitamin D [odds ratio (OR) 1.00; 95% confidence interval (CI) 0.96-1.04]. In the adjusted model for severe disease only serum albumin (OR 0.12; 95%CI 0.02-0.64) and diagnosis by detection of stool toxin (OR 5.87; 95%CI 1.09-31.7) remained independent predictors. We conclude that serum 25-hydroxyvitamin D is not associated with the development of severe disease in patients with CDI.

Development and Validation of Digital Enzyme-Linked Immunosorbent Assays for Ultrasensitive Detection and Quantification of Clostridium difficile Toxins in Stool

The currently available diagnostics for Clostridium difficile infection (CDI) have major limitations. Despite mounting evidence that toxin detection is paramount for diagnosis, conventional toxin immunoassays are insufficiently sensitive and cytotoxicity assays too complex; assays that detect toxigenic organisms (toxigenic culture [TC] and nucleic acid amplification testing [NAAT]) are confounded by asymptomatic colonization by toxigenic C. difficile. We developed ultrasensitive digital enzyme-linked immunosorbent assays (ELISAs) for toxins A and B using single-molecule array technology and validated the assays using (i) culture filtrates from a panel of clinical C. difficile isolates and (ii) 149 adult stool specimens already tested routinely by NAAT. The digital ELISAs detected toxins A and B in stool with limits of detection of 0.45 and 1.5 pg/ml, respectively, quantified toxins across a 4-log range, and detected toxins from all clinical strains studied. Using specimens that were negative by cytotoxicity assay/TC/NAAT, clinical cutoffs were set at 29.4 pg/ml (toxin A) and 23.3 pg/ml (toxin B); the resulting clinical specificities were 96% and 98%, respectively. The toxin B digital ELISA was 100% sensitive versus cytotoxicity assay. Twenty-five percent and 22% of the samples positive by NAAT and TC, respectively, were negative by the toxin B digital ELISA, consistent with the presence of organism but minimal or no toxin. The mean toxin levels by digital ELISA were 1.5- to 1.7-fold higher in five patients with CDI-attributable severe outcomes, versus 68 patients without, but this difference was not statistically significant. Ultrasensitive digital ELISAs for the detection and quantification of toxins A and B in stool can provide a rapid and simple tool for the diagnosis of CDI with both high analytical sensitivity and high clinical specificity.

Evaluation of 3 automated real-time PCR (Xpert C. difficile assay, BD MAX Cdiff, and IMDx C. difficile for Abbott m2000 assay) for detecting Clostridium difficile toxin gene compared to toxigenic culture in stool specimens

We evaluated the performance of the 3 automated systems (Cepheid Xpert, BD MAX, and IMDx C. difficile for Abbott m2000) detecting Clostridium difficile toxin gene compared to toxigenic culture. Of the 254 stool specimens tested, 87 (48 slight, 35 moderate, and 4 heavy growth) were toxigenic culture positive. The overall sensitivities and specificities were 82.8% and 98.8% for Xpert, 81.6% and 95.8% for BD MAX, and 62.1% and 99.4% for IMDx, respectively. The specificity was significantly higher in IMDx than BD MAX (P= 0.03). All stool samples underwent toxin A/B enzyme immunoassay testing, and of the 254 samples, only 29 samples were positive and 2 of them were toxigenic culture negative. Considering the rapidity and high specificity of the real-time PCR assays compared to the toxigenic culture, they can be used as the first test method for C. difficile infection/colonization.

Clostridium difficile infection: New insights into therapeutic options

Clostridium difficile infection (CDI) is an important cause of mortality and morbidity in healthcare settings and represents a major social and economic burden. The major virulence determinants are large clostridial toxins, toxin A (TcdA) and toxin B (TcdB), encoded within the pathogenicity locus. Traditional therapies, such as metronidazole and vancomycin, frequently lead to a vicious circle of recurrences due to their action against normal human microbiome. New disease management strategies together with the development of novel therapeutic and containment approaches are needed in order to better control outbreaks and treat patients. This article provides an overview of currently available CDI treatment options and discusses the most promising therapies under development.

Impact of clinical awareness and diagnostic tests on the underdiagnosis of Clostridium difficile infection

A multicenter study of Clostridium difficile infection (CDI) performed during 2008 in Spain revealed that two of every three episodes went undiagnosed or were misdiagnosed owing to nonsensitive diagnostic tests or lack of clinical suspicion and request. Since then, efforts have been made to improve the diagnostic tests used by laboratories and to increase the awareness of this disease among both clinicians and microbiologists. Our objective was to evaluate the impact of these efforts by assessing the current magnitude of underdiagnosis of CDI in Spain using two point-prevalence studies performed on one day each in January and July of 2013. A total of 111 Spanish laboratories selected all unformed stool specimens received for microbiological diagnosis on these days, and toxigenic culture was performed at a central reference laboratory. Toxigenic isolates were characterized both pheno- and genotypically. The reference laboratory detected 103 episodes of CDI in patients aged 2 years or more. Half (50.5 %) of the episodes were not diagnosed in the participating laboratories, owing to insensitive diagnostic tests (15.5 %) or the lack of clinical suspicion and request (35.0 %). The main ribotypes were 014, 078/126, 001/072, and 106. Ribotype 027 caused 2.9 % of all cases. Despite all the interventions undertaken, CDI remains a highly neglected disease because of the lack of sensitive diagnostic tests in some institutions and, especially, the absence of clinical suspicion, mainly in patients with community-associated CDI. Toxigenic C. difficile should be routinely sought in unformed stools sent for microbiological diagnosis, regardless of their origin.

Clostridium difficile Infection Is More Severe When Toxin Is Detected in the Stool than When Detected Only by a Toxigenic Culture

OBJECTIVE

Clostridium difficile infection (CDI) is the major cause of antibiotic-associated diarrhea in hospital inpatients. Rapid testing for the toxins in stool specimens is inconclusive due to its low sensitivity. Therefore, a two-step method is recommended as the most appropriate approach. The purpose of the present study was to evaluate the differences in the disease severity score between the patients who were glutamate dehydrogenase (GDH)-positive/enzyme immunoassays (EIA) toxin-positive (group A) and those who were GDH-positive/EIA toxin-negative, but who were nonetheless finally confirmed to be toxin-positive by toxigenic culture testing (group B).

METHODS

A rapid detection EIA for GDH and toxin A/B were simultaneously performed for initial screening. Subsequently, the toxin production by bacterial colonies in culture was retested with the same rapid test kit when necessitated by an equivocal result of the initial screening.

RESULTS

A total of 334 fecal specimens were evaluated. Group A consisted of 25 specimens (from 16 patients) and group B consisted of 27 specimens (from 12 patients). The severity score (based on a number of factors, including age, body temperature, serum albumin level and white cell count) of group A and B was 2.2±0.7 and 1.4±0.5, respectively (p=0.002).

CONCLUSION

The cases of CDI in which the toxins were detected by the initial screening test were more severe than those where the toxins were not detected at the initial screening but were identified by the toxigenic culture. In addition, the most significant factors affecting the severity score were an older age and a lower serum albumin level.

Comparison of GenomEra C. difficile and Xpert C. difficile as confirmatory tests in a multistep algorithm for diagnosis of Clostridium difficile infection

We compared two multistep diagnostic algorithms based on C. Diff Quik Chek Complete and, as confirmatory tests, GenomEra C. difficile and Xpert C. difficile. The sensitivity, specificity, positive predictive value, and negative predictive value were 87.2%, 99.7%, 97.1%, and 98.3%, respectively, for the GenomEra-based algorithm and 89.7%, 99.4%, 95.5%, and 98.6%, respectively, for the Xpert-based algorithm. GenomEra represents an alternative to Xpert as a confirmatory test of a multistep algorithm for Clostridium difficile infection (CDI) diagnosis.

Comparing the economic and health benefits of different approaches to diagnosing Clostridium difficile infection

Accurate diagnosis of Clostridium difficile infection (CDI) is essential to effectively managing patients and preventing transmission. Despite the availability of several diagnostic tests, the optimal strategy is debatable and their economic values are unknown. We modified our previously existing C. difficile simulation model to determine the economic value of different CDI diagnostic approaches from the hospital perspective. We evaluated four diagnostic methods for a patient suspected of having CDI: 1) toxin A/B enzyme immunoassay, 2) glutamate dehydrogenase (GDH) antigen/toxin AB combined in one test, 3) nucleic acid amplification test (NAAT), and 4) GDH antigen/toxin AB combination test with NAAT confirmation of indeterminate results. Sensitivity analysis varied the proportion of those tested with clinically significant diarrhoea, the probability of CDI, NAAT cost and CDI treatment delay resulting from a false-negative test, length of stay and diagnostic sensitivity and specificity. The GDH/toxin AB plus NAAT approach leads to the timeliest treatment with the fewest unnecessary treatments given, resulted in the best bed management and generated the lowest cost. The NAAT-alone approach also leads to timely treatment. The GDH/toxin AB diagnostic (without NAAT confirmation) approach resulted in a large number of delayed treatments, but results in the fewest secondary colonisations. Results were robust to the sensitivity analysis. Choosing the right diagnostic approach is a matter of cost and test accuracy. GDH/toxin AB plus NAAT diagnosis led to the timeliest treatment and was the least costly.

European Society of Clinical Microbiology and Infectious Diseases: update of the treatment guidance document for Clostridium difficile infection

In 2009 the first European Society of Clinical Microbiology and Infection (ESCMID) treatment guidance document for Clostridium difficile infection (CDI) was published. The guideline has been applied widely in clinical practice. In this document an update and review on the comparative effectiveness of the currently available treatment modalities of CDI is given, thereby providing evidence-based recommendations on this issue. A computerized literature search was carried out to investigate randomized and non-randomized trials investigating the effect of an intervention on the clinical outcome of CDI. The Grades of Recommendation Assessment, Development and Evaluation (GRADE) system was used to grade the strength of our recommendations and the quality of the evidence. The ESCMID and an international team of experts from 11 European countries supported the process. To improve clinical guidance in the treatment of CDI, recommendations are specified for various patient groups, e.g. initial non-severe disease, severe CDI, first recurrence or risk for recurrent disease, multiple recurrences and treatment of CDI when oral administration is not possible. Treatment options that are reviewed include: antibiotics, toxin-binding resins and polymers, immunotherapy, probiotics, and faecal or bacterial intestinal transplantation. Except for very mild CDI that is clearly induced by antibiotic usage antibiotic treatment is advised. The main antibiotics that are recommended are metronidazole, vancomycin and fidaxomicin. Faecal transplantation is strongly recommended for multiple recurrent CDI. In case of perforation of the colon and/or systemic inflammation and deteriorating clinical condition despite antibiotic therapy, total abdominal colectomy or diverting loop ileostomy combined with colonic lavage is recommended.

Point-of-Care Testing for Clostridium Difficile Infection: A Real-World Feasibility Study of a Rapid Molecular Test in Two Hospital Settings

Introduction

In the developed world, Clostridium difficile infection (CDI) is the most important cause of nosocomial infectious diarrhea. In addition to providing epidemiological data and helping to indicate that a local outbreak may be occurring, laboratory tests are used to augment clinical decisions on individual patients. Very rarely do diagnostic tests provide results at the point of decision making; in the intervening period between requesting investigations on a patient with suspected CDI and return of the laboratory result, decisions must be made regarding patient isolation and treatment.

Methods

A 22-month, real-world feasibility study was conducted in patients with clinically significant diarrhea, in a London Hospital between March 2011 and January 2013, in three older persons’ wards and two intensive care units (ICUs) to determine acceptability, ease of use, change in turnaround time and clinical utility of a rapid, polymerase chain reaction (PCR)-based point-of-care test (POCT) (Cepheid GeneXpert^®, Sunnyvale, California, USA) for diagnosis of Clostridium difficile. Nurses in the older persons’ ward and laboratory technicians in the ICU were trained to perform the test. Residual samples were sent to the centralized laboratory for parallel testing using a two-step algorithm.

Results

A total of 335 samples were tested using the POCT with a median turnaround time of 1.85 h compared with 18 h for the centralized laboratory test. Overall agreement with centralized laboratory testing was 98.1%. Discrepant samples were more frequent on elderly wards than ICU. Overall 20/335 (6%) processing errors were encountered and were highest in the first few months of the study. Significantly more processing errors occurred on the older persons’ wards 13/102 (12.7%) than on ICU 7/271 (2.6%). Older persons’ patients who had POCT were significantly less likely to have a test requested for bacterial stool culture (3.1% vs. 10.9% p = 0.044). This difference was not observed in the ICU patients. No other differences in ancillary test requesting, mortality or length of stay were observed.

Conclusions

The majority of users reported that the POCT was easy to perform and was an acceptable part of their job. POCT using this system is feasible and acceptable to nursing staff and technicians working within these two hospital-based settings.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-014-0038-6) contains supplementary material, which is available to authorized users.

Clinical characteristics and outcome of patients with Clostridium difficile infection diagnosed by PCR versus a three-step algorithm

Clinical features of Clostridium difficile infections (CDI) detected by PCR, but not by conventional methods, are poorly understood. We compared the clinical features of CDI cases detected by PCR only and cases detected by both PCR and a three-step algorithm. We performed a retrospective cohort study of patients fulfilling a standardized definition over a 13-month period. Stool specimens were tested in parallel by PCR and an algorithm based on enzyme immunoassay and cytotoxicity assay (EIA/CCA). Clinical features of CDI cases detected by PCR only and cases detected by PCR and EIA/CCA were compared by univariate logistic regression. In all, 97 patients (31 PCR+ and 66 PCR+EIA/CCA+) met the inclusion criteria. Compared with cases detected by both PCR and EIA/CCA, CDI cases detected by PCR only were younger (65.4 versus 76.3 years; p 0.001), had a lower absolute neutrophil count (mean, 9.4 × 10(9) /L versus 12.5 × 10(9) /L; p 0.04), were less likely to receive oral vancomycin (2/31 versus 25/66; p 0.005) or combination therapy (0/31 versus 16/66; p 0.04), and had fewer complications (6/31 versus 29/66; p 0.02), despite presenting a higher number of bowel movements on the day of diagnosis (median, 6.0 versus 3.0; p 0.02). They had also a lower C. difficile faecal bacterial load (mean, 5.04 versus 6.89 log10 CFU/g; p <0.001). The CDI cases detected by PCR only and cases detected by both PCR and EIA/CCA have different clinical features, but whether these two populations can be managed differently remains to be determined.

Evaluation of a chromogenic culture medium for the detection of Clostridium difficile

PURPOSE

Clostridium difficile (C. difficile) is an important cause of nosocomial diarrhea. Diagnostic methods for detection of C. difficile infection (CDI) are shifting to molecular techniques, which are faster and more sensitive than conventional methods. Although recent advances in these methods have been made in terms of their cost-benefit, ease of use, and turnaround time, anaerobic culture remains an important method for detection of CDI.

MATERIALS AND METHODS

In efforts to evaluate a novel chromogenic medium for the detection of C. difficile (chromID CD agar), 289 fecal specimens were analyzed using two other culture media of blood agar and cycloserine-cefoxitin-fructose-egg yolk agar while enzyme immunosorbent assay and polymerase chain reaction-based assay were used for toxin detection.

RESULTS

ChromID showed the highest detection rate among the three culture media. Both positive rate and sensitivity were higher from chromID than other culture media. ChromID was better at detecting toxin producing C. difficile at 24 h and showed the highest detection rate at both 24 h and 48 h.

CONCLUSION

Simultaneous use of toxin assay and anaerobic culture has been considered as the most accurate and sensitive diagnostic approach of CDI. Utilization of a more rapid and sensitive chromogenic medium will aid in the dianogsis of CDI.

How do hospital professionals involved in a randomised controlled trial perceive the value of genotyping vs. PCR-ribotyping for control of hospital acquired C. difficile infections?

Background

Despite scientific advances in typing of C. difficile strains very little is known about how hospital staff use typing results during periods of increased incidence (PIIs). This qualitative study, undertaken alongside a randomised controlled trial (RCT), explored this issue. The trial compared ribotyping versus more rapid genotyping (MLVA or multilocus variable repeat analysis) and found no significant difference in post 48 hour cases (C difficile transmissions).

Methods

In-depth qualitative interviews with senior staff in 11/16 hospital trusts in the trial (5 MLVA and 6 Ribotyping). Semi-structured interviews were conducted at end of the trial period. Transcripts were content analysed using framework analysis supported by NVivo-8 software. Common sub-themes were extracted by two researchers independently. These were compared and organised into over-arching categories or ‘super-ordinate themes’.

Results

The trial recorded that 45% of typing tests had some impact on infection control (IC) activities. Interviews indicated that tests had little impact on initial IC decisions. These were driven by hospital protocols and automatically triggered when a PII was identified. To influence decision-making, a laboratory turnaround time < 3 days (ideally 24 hours) was suggested; MLVA turnaround time was 5.3 days. Typing results were predominantly used to modify initiated IC activities such as ward cleaning, audits of practice or staff training; major decisions (e.g. ward closure) were unaffected. Organisational factors could limit utilisation of MLVA results. Results were twice as likely to be reported as ‘aiding management’ (indirect benefit) than impacting on IC activities (direct effect). Some interviewees considered test results provided reassurance about earlier IC decisions; others identified secondary benefits on organisational culture. An underlying benefit of improved discrimination provided by MLVA typing was the ability to explore epidemiology associated with CDI cases in a hospital more thoroughly.

Conclusions

Ribotyping and MLVA are both valued by users. MLVA had little additional direct impact on initial infection control decisions. This would require reduced turnaround time. The major impact is adjustments to earlier IC measures and retrospective reassurance. For this, turnaround time is less important than discriminatory power. The potential remains for wider use of genotyping to examine transmission routes.

Control of Clostridium difficile infection in the hospital setting

Clostridium difficile infection (CDI) has emerged as a leading challenge in the control of healthcare-associated infection (HCAI). The epidemiology of CDI has changed dramatically, this is associated with emergence of 'hypervirulent' strains, particularly PCR ribotype 027. Despite the epidemic spread of these strains, there are recent reports of decreasing incidence from healthcare facilities where multi-facetted targeted control programs have been implemented. We consider these changes in epidemiology and reflect on the tools available to control CDI in the hospital setting. The precise repertoire of measures adopted and emphasis on different interventions will vary, not only between healthcare systems, but also within different institutions within the same healthcare system. Finally, we consider both the sustainability of reductions already achieved, and the potential to reduce CDI further. This takes account of newly emerging data on more recent changes in the epidemiology of CDI, and the potential of novel interventions to decrease the burden of disease.

Clinical update for the diagnosis and treatment of Clostridium difficile infection

Clostridium difficile infection (CDI) presents a rapidly evolving challenge in the battle against hospital-acquired infections. Recent advances in CDI diagnosis and management include rapid changes in diagnostic approach with the introduction of newer tests, such as detection of glutamate dehydrogenase in stool and polymerase chain reaction to detect the gene for toxin production, which will soon revolutionize the diagnostic approach to CDI. New medications and multiple medical society guidelines have introduced changing concepts in the definitions of severity of CDI and the choice of therapeutic agents, while rapid expansion of data on the efficacy of fecal microbiota transplantation heralds a revolutionary change in the management of patients suffering multiple relapses of CDI. Through a comprehensive review of current medical literature, this article aims to offer an intensive review of the current state of CDI diagnosis, discuss the strengths and limitations of available laboratory tests, compare both current and future treatments options and offer recommendations for best practice strategies.

Portrait Toxigenic Clostridium difficile assay, an isothermal amplification assay detects toxigenic C. difficile in clinical stool specimens

The Portrait Toxigenic Clostridium difficile assay is a rapid, qualitative assay for the detection of the tcdB gene of C. difficile in stool specimens from patients suspected of C. difficile infections, and received 510(k) clearance by the US FDA in March 2012. The Portrait Toxigenic C. difficile assay combines novel blocked-primer-mediated helicase-dependent multiplex amplification (bpHDA) technology and chip-based detection in an automated sample-to-result format. The assay requires minimal sample preparation and results are available within 90 min. In a multicenter evaluation, the Portrait Toxigenic C. difficile assay had a sensitivity of 98.2% and specificity of 92.8% compared with toxigenic culture. A comparative study between the Portrait Toxigenic C. difficile assay and three FDA-cleared molecular assays for the detection of toxigenic C. difficile exhibited a high degree of agreement (93.8-97.5%). The Portrait Toxigenic C. difficile assay provides a simple, cost-effective method with broad applicability to panel-based approaches, potentially simplifying workflow.

Clinical comparison of Simplexa universal direct and BD GeneOhm tests for detection of toxigenic Clostridium difficile in stool samples

We compared the performance characteristics of the Simplexa universal direct (Focus Diagnostics, Cypress, CA) and BD GeneOhm (BD Diagnostics/GeneOhm Sciences, San Diego, CA) tests for detection of toxigenic Clostridium difficile in 459 stool samples (9.4% positive). The observed agreement for the results of the two tests with 452 samples with valid test results was 98.2% (kappa, 0.9; P value of 0.73 by the McNemar test). When samples with discordant or invalid results were retested, the agreement increased to 100%.

Differences in outcome according to Clostridium difficile testing method: a prospective multicentre diagnostic validation study of C difficile infection

Background

Diagnosis of Clostridium difficile infection is controversial because of many laboratory methods, compounded by two reference methods. Cytotoxigenic culture detects toxigenic C difficile and gives a positive result more frequently (eg, because of colonisation, which means that individuals can have the bacterium but no free toxin) than does the cytotoxin assay, which detects preformed toxin in faeces. We aimed to validate the reference methods according to clinical outcomes and to derive an optimum laboratory diagnostic algorithm for C difficile infection.

Methods

In this prospective, multicentre study, we did cytotoxigenic culture and cytotoxin assays on 12 420 faecal samples in four UK laboratories. We also performed tests that represent the three main targets for C difficile detection: bacterium (glutamate dehydrogenase), toxins, or toxin genes. We used routine blood test results, length of hospital stay, and 30-day mortality to clinically validate the reference methods. Data were categorised by reference method result: group 1, cytotoxin assay positive; group 2, cytotoxigenic culture positive and cytotoxin assay negative; and group 3, both reference methods negative.

Findings

Clinical and reference assay data were available for 6522 inpatient episodes. On univariate analysis, mortality was significantly higher in group 1 than in group 2 (72/435 [16·6%] vs 20/207 [9·7%], p=0·044) and in group 3 (503/5880 [8·6%], p<0·001), but not in group 2 compared with group 3 (p=0·4). A multivariate analysis accounting for potential confounders confirmed the mortality differences between groups 1 and 3 (OR 1·61, 95% CI 1·12–2·31). Multistage algorithms performed better than did standalone assays.

Interpretation

We noted no increase in mortality when toxigenic C difficile alone was present. Toxin (cytotoxin assay) positivity correlated with clinical outcome, and so this reference method best defines true cases of C difficile infection. A new diagnostic category of potential C difficile excretor (cytotoxigenic culture positive but cytotoxin assay negative) could be used to characterise patients with diarrhoea that is probably not due to C difficile infection, but who can cause cross-infection.

Funding

Department of Health and Health Protection Agency, UK.

Correlation between Clostridium difficile bacterial load, commercial real-time PCR cycle thresholds, and results of diagnostic tests based on enzyme immunoassay and cell culture cytotoxicity assay

The impact of Clostridium difficile fecal loads on diagnostic test results is poorly understood, but it may have clinical importance. In this study, we investigated the relationship between C. difficile fecal load and the results of four assays: a glutamate dehydrogenase (GDH) enzyme immunoassay (EIA), a toxin A/B antigen EIA (ToxAB), a cell culture cytotoxicity assay (CCA), and PCR targeting the tcdB gene. We also compared the PCR cycle threshold (CT) with the results of quantitative culture using Spearman's rank correlation coefficient. Finally, we sequenced the genomes of 24 strains with different detection profiles. A total of 203 clinical samples harboring toxigenic C. difficile were analyzed and sorted into one of four groups: 17 PCR(+) (group 1), 37 PCR(+) GDH(+) (group 2), 24 PCR(+) GDH(+) CCA(+) (group 3), and 125 PCR(+) GDH(+) ToxAB(+) (group 4). The overall median fecal load in log10 CFU/g was 6.67 (interquartile range [IQR], 5.57 to 7.54). The median fecal bacterial load of groups 1, 2, 3, and 4 were 4.15 (IQR, 3.00 to 4.98), 5.74 (IQR, 4.75 to 6.16), 6.20 (IQR, 5.23 to 6.80), and 7.08 (IQR, 6.35 to 7.83), respectively. Group 1 samples had lower fecal loads than those from each of the other groups (P < 0.001). Group 2 samples had lower fecal loads than those from groups 3 and 4 (P < 0.001). There was a significant correlation between PCR CT and fecal loads (ρ = -0.697; P < 0.001). NAP1 strains were associated with the detection of toxins by EIA or CCA (P = 0.041). This study demonstrates an association between C. difficile fecal load and the results of routinely used diagnostic tests.

Clinical relevance of a positive molecular test in the diagnosis of Clostridium difficile infection

BACKGROUND

In 2011, the Department of Health advised that a two-stage test approach should be used to improve accuracy of Clostridium difficile infection (CDI) diagnosis. No specific test protocol was established at that time.

AIM

To compare clinical features of inpatient CDI cases identified by toxin enzyme immunoassay (EIA) with those identified as polymerase chain reaction (PCR) positive but toxin EIA negative.

METHODS

During a six-month period (2011-2012), 2181 liquid faeces samples submitted to North Bristol NHS Trust were tested by EIA for both toxin and glutamate dehydrogenase (GDH). A total of 215 toxin or GDH EIA-positive samples were tested by Cepheid Xpert PCR assay; 128 clinically evaluable inpatients were grouped by test result, and their duration of diarrhoea and 14-day mortality compared.

FINDINGS

Inpatients with a positive PCR but negative toxin EIA had a significantly lower 14-day all-cause mortality [11%; 95% confidence interval (CI): 4-23%] than patients with a positive PCR and positive toxin EIA test (37%; 95% CI: 19-59%; P = 0.01), and a smaller proportion of patients had prolonged diarrhoea (>5 days or unresolved at death: 19%; CI: 9-32%, vs 67%; CI: 45-84%; P < 0.001). A positive toxin EIA test was a significant independent predictor of death [odds ratio (OR): 4.7, 95% CI: 1.4-15.4; P = 0.01] and prolonged diarrhoea (OR: 8.6; CI: 2.9-25.6; P < 0.001), but a positive PCR (given positive GDH EIA) was not.

CONCLUSION

The clinical significance of a positive PCR result without a positive toxin EIA is questionable; such a result is associated with a significantly lower mortality and shorter duration of symptoms than patients with a positive toxin EIA.