Economic evaluation of laboratory testing strategies for hospital-associated Clostridium difficile infection

Budget Impact Analysis of Adopting a One-Step Nucleic Acid Amplification Testing (NAAT) Alone Diagnostic Pathway for Clostridioides difficile in Japan Compared to a Two-Step Algorithm with Glutamate Dehydrogenase/Toxin Followed by NAAT

Clostridioides difficile infection (CDI) is a major healthcare-associated infection that leads to a significant health economic burden in Japan. Using a decision tree model, we evaluated the budget impact of adopting a one-step nucleic acid amplification test (NAAT) alone pathway compared to a two-step diagnostic algorithm with glutamate dehydrogenase (GDH) and toxin antigen, followed by NAAT. The analysis was conducted from the government payer's perspective for 100,000 symptomatic, hospitalized adults requiring a CDI diagnostic test. One-way sensitivity analysis was conducted for all data inputs. The NAAT alone strategy costed JPY 225,886,360 (USD 2,424,714) more, but was more effective, resulting in 1749 more patients accurately diagnosed and 91 fewer deaths compared to the two-step algorithm. Additionally, the NAAT alone pathway costed JPY 26,146 (USD 281) less per true positive CDI diagnosed. The total budget impact, and cost per CDI diagnosed was most sensitive to GDH sensitivity in one-way sensitivity analysis, where a lower GDH sensitivity resulted in greater cost savings with the NAAT alone pathway. Findings from this budget impact analysis can guide the adoption of a NAAT alone pathway for CDI diagnosis in Japan.

Evaluation of the Cepheid Xpert C. difficile diagnostic assay: an update meta-analysis

Background

Accurate and rapid diagnosis of Clostridium difficile infection (CDI) is critical for effective patient management and implementation of infection control measures to prevent transmission.

Objectives

We updated our previous meta-analysis to provide a more reliable evidence base for the clinical diagnosis of Xpert C. difficile (Xpert C. difficile) assay.

Methods

We searched PubMed, EMBASE, Cochrane Library, Chinese National Knowledge Infrastructure (CNKI), and the Chinese Biomedical Literature Database (CBM) databases to identify studies according to predetermined criteria. STATA 13.0 software was used to analyze the tests for sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and area under the summary receiver operating characteristic curves (AUC). QUADAS-2 was used to assess the quality of included studies with RevMan 5.2. Heterogeneity in accuracy measures was tested with Spearman correlation coefficient and chi-square. Meta-regressions and subgroup analyses were performed to figure out the potential sources of heterogeneity. Model diagnostics were used to evaluate the veracity of the data.

Results

A total of 26 studies were included in the meta-analysis. The pooled sensitivity (95% confidence intervals [CI]) for diagnosis was 0.97(0.95–0.98), and specificity was 0.96(0.95–0.97). The AUC was 0.99 (0.98–1.00). Model diagnostics confirmed the robustness of our meta-analysis’s results. Significant heterogeneity was still observed when we pooled most of the accuracy measures of selected studies. Meta-regression and subgroup analyses showed that the sample size and type, ethnicity, and disease prevalence might be the conspicuous sources of heterogeneity.

Conclusions

The up-to-date meta-analysis showed the Xpert CD assay had good accuracy for detecting CDI. However, the diagnosis of CDI must combine clinical presentation with diagnostic testing to better answer the question of whether the patient actually has CDI in the future, and inclusion of preanalytical parameters and clinical outcomes in study design would provide a more objective evidence base.

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.

Impact of a division-wide bundle on hospital-acquired Clostridioides difficile cases, antibiotic days of therapy, testing appropriateness, and associated financial costs

Introduction:

Updated international guidelines recommend the use of a two-step algorithm (glutamate dehydrogenase [GDH] or nucleic-acid amplification test [NAAT] plus toxin) rather than NAAT alone for the diagnosis of Clostridioides difficile (formerly Clostridium difficile) infections. The goal of our project was to evaluate the impact of a new bundle on the rate of hospital-acquired C. difficile infections (CDIs), hospital-acquired CDI standardized infection ratio (SIR), antibiotic days of therapy (DOT), and financial cost.

Materials and Methods:

The new bundle was implemented in April 2018. This bundle was implemented across five hospitals in Catholic Health Initiatives (CHI) Texas Division. The bundle included a switch from NAAT to a two-step process (GDH and toxin). We placed the new test in an order panel which included enteric isolation and required indications for C. difficile testing. We used quarterly data pre- and post-intervention to calculate SIR and DOT.

Results:

In the pre-intervention period, 15.5% of the total 3513 C. difficile NAAT was positive. In the post-intervention period, 5.7% of a total of 2845 GDH and toxin assays was positive for both GDH and toxin (P < 0.0001). SIR, which adjusts for denominator and change in testing methodology, also dropped from 1.02 to 0.43. The estimated cost associated with positive C. difficile cases dropped from 1,932,150 USD to 1,113,800 USD with an estimated yearly cost saving of 794,150 USD. Compliance with enteric isolation improved from 73.1% to 92.5% (P = 0.008).

Conclusion:

The new testing bundle led to a marked reduction in hospital-acquired CDI and unnecessary treatment, reduction in C. difficile testing, an increase in compliance with enteric isolation, and significant cost savings.

Burden and risk factors for inappropriate Clostridioides Difficile infection testing among hospitalized patients

BACKGROUND

The purpose of this study was to identify the burden and risk factors for inappropriate Clostridioides difficile infection (CDI) testing.

METHODS

This was a retrospective cohort study among adults hospitalized between 2010 and 2019. Inappropriate CDI testing was defined as a formed stool specimen, an order within 7 days of a previously negative test, or an order within 24 hours of laxative administration.

RESULTS

A total of 51,302 CDI orders were placed for 29,840 unique patients. 59% were appropriate and 41% were inappropriate. An additional 24% of the appropriate orders never resulted. Risk factors for inappropriate testing included orders placed by a nurse practitioner, orders placed by high-ordering providers, specific hospital units, fever, and leukocytosis.

CONCLUSIONS

Nearly half of all CDI orders were inappropriate among hospitalized patients, and an additional 24% of test results never returned. Provider- and patient-level risk factors included type of provider, specific hospital units, and signs of sepsis.

Evaluation of the Cost-effectiveness of Infection Control Strategies to Reduce Hospital-Onset Clostridioides difficile Infection

Importance

Clostridioides difficile infection is the most common hospital-acquired infection in the United States, yet few studies have evaluated the cost-effectiveness of infection control initiatives targeting C difficile.

Objective

To compare the cost-effectiveness of 9 C difficile single intervention strategies and 8 multi-intervention bundles.

Design, Setting, and Participants

This economic evaluation was conducted in a simulated 200-bed tertiary, acute care, adult hospital. The study relied on clinical outcomes from a published agent-based simulation model of C difficile transmission. The model included 4 agent types (ie, patients, nurses, physicians, and visitors). Cost and utility estimates were derived from the literature.

Interventions

Daily sporicidal cleaning, terminal sporicidal cleaning, health care worker hand hygiene, patient hand hygiene, visitor hand hygiene, health care worker contact precautions, visitor contact precautions, C difficile screening at admission, and reduced intrahospital patient transfers.

Main Outcomes and Measures

Cost-effectiveness was evaluated from the hospital perspective and defined by 2 measures: cost per hospital-onset C difficile infection averted and cost per quality-adjusted life-year (QALY).

Results

In this agent-based model of a simulated 200-bed tertiary, acute care, adult hospital, 5 of 9 single intervention strategies were dominant, reducing cost, increasing QALYs, and averting hospital-onset C difficile infection compared with baseline standard hospital practices. They were daily cleaning (most cost-effective, saving $358 268 and 36.8 QALYs annually), health care worker hand hygiene, patient hand hygiene, terminal cleaning, and reducing intrahospital patient transfers. Screening at admission cost $1283/QALY, while health care worker contact precautions and visitor hand hygiene interventions cost $123 264/QALY and $5 730 987/QALY, respectively. Visitor contact precautions was dominated, with increased cost and decreased QALYs. Adding screening, health care worker hand hygiene, and patient hand hygiene sequentially to the daily cleaning intervention formed 2-pronged, 3-pronged, and 4-pronged multi-intervention bundles that cost an additional $29 616/QALY, $50 196/QALY, and $146 792/QALY, respectively.

Conclusions and Relevance

The findings of this study suggest that institutions should seek to streamline their infection control initiatives and prioritize a smaller number of highly cost-effective interventions. Daily sporicidal cleaning was among several cost-saving strategies that could be prioritized over minimally effective, costly strategies, such as visitor contact precautions.

Cost-Effectiveness Analysis of Four Common Diagnostic Methods for Clostridioides difficile Infection

BACKGROUND

No studies have evaluated the cost-effectiveness of single and two-step different diagnostic test strategies for Clostridioides difficile infection (CDI), including direct and indirect costs.

OBJECTIVE

To evaluate the cost-effectiveness of commonly available diagnostic tests for CDI including nucleic acid amplification testing (NAAT) alone, glutamate dehydrogenase followed by enzyme immunoassay for toxin (GDH/EIA), GDH then NAAT (GDH/NAAT), and NAAT then EIA (NAAT/EIA).

DESIGN

Decision tree model from the US societal perspective with inputs derived from the literature. Willingness-to-pay threshold was set at $150,000 per quality-adjusted life year (QALY) gained. To assess the impact of uncertainty in model inputs on the findings, we performed one-way and probabilistic sensitivity analyses.

PARTICIPANTS

We conducted the analysis to represent a population aged 65 years old with diarrhea who received a CDI diagnostic test.

MAIN MEASURES

Incremental cost-effectiveness ratios (ICER) and incremental net monetary benefits (INMB).

KEY RESULTS

NAAT alone was the most cost-effective approach overall; GDH/NAAT was the most cost-effective two-step option. NAAT alone led to the highest QALYs gained, at an incremental cost of $54,547 (vs. GDH/NAAT), $55,410 (vs. GDH/EIA), and $50,231 (vs. NAAT/EIA) per QALY gained. NAAT/EIA was not cost-effective compared to any other strategy. GDH/NAAT resulted in a higher QALY compared to GDH/EIA, at an incremental cost of $96,841 per QALY gained. Variability in the likelihood of comorbidities, CDI probability, and age at disease onset did not substantially change the results. One-way sensitivity analyses showed that results were most sensitive to likelihood of recurrence, followed by CDI mortality rate and probability of severe CDI. Probabilistic sensitivity analyses explored known uncertainties in the base case and confirmed the robustness of the results.

CONCLUSIONS

NAAT alone and GDH/NAAT (among the two-step options) were the most cost-effective diagnostic test approaches for CDI.

Laboratory Tests for the Diagnosis of Clostridium difficile

Clostridium (reclassified as " Clostridioides ") difficile is an anaerobic, gram-positive bacterium that causes significant disease through elaboration of two potent toxins in patients whose normal gut microbiota has been altered through antimicrobial or chemotherapeutic agents (dysbiosis). The optimum method of laboratory diagnosis is still somewhat controversial. Recent practice guidelines published by professional societies recommend a two-step approach beginning with a test for glutamate dehydrogenase (GDH), followed by a toxin test and/or a nucleic acid test. Alternatively, in institutions where established clinical algorithms guide testing, a nucleic acid test alone is acceptable. Nucleic acid tests are the methods of choice in approximately 50% of laboratories in the United States. These tests are considered as the most sensitive methods for detection of C. difficile in stool and are the least specific. Because of the lower specificity with nucleic acid tests, some clinicians believe that toxin enzyme immunoassays are better predictors of disease, despite their known poor performance in certain patient populations. This review will discuss the advantages and disadvantages of the currently available test methods for the diagnosis of C. difficile with a brief mention of some novel assays that are currently in clinical trials.

A Laboratory Medicine Best Practices Systematic Review and Meta-analysis of Nucleic Acid Amplification Tests (NAATs) and Algorithms Including NAATs for the Diagnosis of Clostridioides (Clostridium) difficile in Adults

The evidence base for the optimal laboratory diagnosis of Clostridioides (Clostridium) difficile in adults is currently unresolved due to the uncertain performance characteristics and various combinations of tests. This systematic review evaluates the diagnostic accuracy of laboratory testing algorithms that include nucleic acid amplification tests (NAATs) to detect the presence of C. difficile The systematic review and meta-analysis included eligible studies (those that had PICO [population, intervention, comparison, outcome] elements) that assessed the diagnostic accuracy of NAAT alone or following glutamate dehydrogenase (GDH) enzyme immunoassays (EIAs) or GDH EIAs plus C. difficile toxin EIAs (toxin). The diagnostic yield of NAAT for repeat testing after an initial negative result was also assessed. Two hundred thirty-eight studies met inclusion criteria. Seventy-two of these studies had sufficient data for meta-analysis. The strength of evidence ranged from high to insufficient. The uses of NAAT only, GDH-positive EIA followed by NAAT, and GDH-positive/toxin-negative EIA followed by NAAT are all recommended as American Society for Microbiology (ASM) best practices for the detection of the C. difficile toxin gene or organism. Meta-analysis of published evidence supports the use of testing algorithms that use NAAT alone or in combination with GDH or GDH plus toxin EIA to detect the presence of C. difficile in adults. There is insufficient evidence to recommend against repeat testing of the sample using NAAT after an initial negative result due to a lack of evidence of harm (i.e., financial, length of stay, or delay of treatment) as specified by the Laboratory Medicine Best Practices (LMBP) systematic review method in making such an assessment. Findings from this systematic review provide clarity to diagnostic testing strategies and highlight gaps, such as low numbers of GDH/toxin/PCR studies, in existing evidence on diagnostic performance, which can be used to guide future clinical research studies.

Cytoskeletal Tropomyosin as a Biomarker in Clostridium difficile Infection

Background

Current diagnostics of Clostridium difficile infection (CDI) heavily relies on detection of the disease-causing organism. The objective of this study was to investigate a cytoskeletal protein, tropomyosin (Tpm), as a CDI biomarker.

Methods

Fecal Tpm was tested by monoclonal antibodies (mAbs) in a 12-month prospective study. Remnant diarrheal clinical specimens and relevant clinical data were collected. The CDI positive (CDI⁺, n = 230) and CDI negative (CDI^-, n = 228) groups were composed of samples testing positive or negative by polymerase chain reaction (PCR) (Xpert^® C. difficile/Epi, Cepheid), respectively. The other enteric pathogen (OEP) group (n = 52) was composed of specimens tested for the presence of other enteric pathogens or parasites by routine testing methods. Extracted fecal Tpm was detected by Western blot and the results were correlated with CDI based on clinical and microbiology laboratory data.

Results

A total of 510 stool specimens were tested. Tpm is not stable in stool, suggesting the utility of fresh specimens. In the CDI⁺ group, specificity and sensitivity of Tpm detection in correlation with a CDI were 93.2% and 53.7%, respectively, when only "true CDI" and "not CDI" were analyzed (110 samples). For CDI⁺ samples, 23% did not satisfy CDI clinical signs. Tpm positives in the CDI^- group (8.3%) had inflammatory bowel diseases.

Conclusion

Tpm has a potential role as a CDI biomarker in combination with C. difficile PCR and an appropriate clinical evaluation. However, non-muscle Tpm, as a biomarker for CDI, suffers from a low sensitivity in our study. Therefore further investigation using larger cohorts is needed.

Model-based economic evaluations of diagnostic point of care tests were rarely fit for purpose

OBJECTIVES

Linked evidence models are recommended to predict health benefits and cost-effectiveness of diagnostic tests. We considered how published models accounted for changes in patient pathways that occur with point of care tests (POCTs) and their impact on patient health and costs.

STUDY DESIGN AND SETTING

Model-based evaluations of diagnostic POCTs published from 2004 to 2017 were identified from searching six databases. For each model, we assessed the outcomes considered, and whether reduced time to diagnosis and increased access to testing affected patient health and costs.

RESULTS

Seventy-four model-based evaluations were included: 95% incorporated evidence on test accuracy, but 34% only assessed intermediate outcomes such as rates of correct diagnosis. Of 54 models where POCTs reduced testing time, 39% addressed the economic and 37% addressed the health benefits of faster diagnosis. No model considered differences in access to tests.

CONCLUSION

Many models fail to capture the effects of POCTs in increasing access, advancing speed of diagnosis and treatment, and reducing anxiety and the associated costs. Many only consider the impact of testing from changes in accuracy. Ensuring models incorporate changes in patient pathways from faster and more accessible testing will lead to economic evaluations that better reflect the impact of POCTs.

Quantitative Thresholds Enable Accurate Identification of Clostridium difficile Infection by the Luminex xTAG Gastrointestinal Pathogen Panel

Clostridium difficile colonizes the gastrointestinal (GI) tract, resulting in either asymptomatic carriage or a spectrum of diarrheal illness. If clinical suspicion for C. difficile is low, stool samples are often submitted for analysis by multiplex molecular assays capable of detecting multiple GI pathogens, and some institutions do not report this organism due to concerns for high false-positive rates. Since clinical disease correlates with organism burden and molecular assays yield quantitative data, we hypothesized that numerical cutoffs could be utilized to improve the specificity of the Luminex xTAG GI pathogen panel (GPP) for C. difficile infection. Analysis of cotested liquid stool samples (n = 1,105) identified a GPP median fluorescence intensity (MFI) value cutoff of ≥1,200 to be predictive of two-step algorithm (2-SA; 96.4% concordance) and toxin enzyme immunoassay (EIA) positivity. Application of this cutoff to a second cotested data set (n = 1,428) yielded 96.5% concordance. To determine test performance characteristics, concordant results were deemed positive or negative, and discordant results were adjudicated via chart review. Test performance characteristics for the MFI cutoff of ≥150 (standard), MFI cutoff of ≥1,200, and 2-SA were as follows (respectively): concordance, 95, 96, and 97%; sensitivity, 93, 78, and 90%; specificity, 95, 98, and 98%; positive predictive value, 67, 82, and 81%;, and negative predictive value, 99, 98, and 99%. To capture the high sensitivity for organism detection (MFI of ≥150) and high specificity for active infection (MFI of ≥1,200), we developed and applied a reporting algorithm to interpret GPP data from patients (n = 563) with clinician orders only for syndromic panel testing, thus enabling accurate reporting of C. difficile for 95% of samples (514 negative and 5 true positives) irrespective of initial clinical suspicion and without the need for additional testing.

Advances in the diagnosis and treatment of Clostridium difficile infections

Clostridium difficile is a leading cause of antibiotic-associated diarrhea worldwide. The diagnosis of C. difficile infection (CDI) requires both clinical manifestations and a positive laboratory test for C. difficile and/or its toxins. While antibiotic therapy is the treatment of choice for CDI, there are relatively few classes of effective antibiotics currently available. Therefore, the development of novel antibiotics and/or alternative treatment strategies for CDI has received a great deal of attention in recent years. A number of emerging agents such as cadazolid, surotomycin, ridinilazole, and bezlotoxumab have demonstrated activity against C. difficile; some of these have been approved for limited clinical use and some are in clinical trials. In addition, other approaches such as early and accurate diagnosis of CDI as well as disease prevention are important for clinical management. While the toxigenic culture and the cell cytotoxicity neutralization assay are still recognized as the gold standard for the diagnosis of CDI, new diagnostic approaches such as nucleic acid amplification methods have become available. In this review, we will discuss both current and emerging diagnostic and therapeutic modalities for CDI.

Potential of real-time PCR threshold cycle (CT) to predict presence of free toxin and clinically relevant C. difficile infection (CDI) in patients with cancer

OBJECTIVES

Clostridium difficile infection (CDI) is a toxin-mediated disease. Oncology patients are at increased risk for developing CDI. Diagnosis of CDI by PCR has led to misclassification of some C. difficile carriers as CDI cases. We determined if an optimized C. difficile PCR cycle threshold value (C_T) could reliably predict presence of free toxin, and in turn improve the utility of PCR in detecting clinically relevant CDI in oncology patients.

METHODS

183 consecutive patients positive for C. difficile by the Xpert C. difficile were additionally tested using the cell culture cytotoxicity neutralization assay (CYT) and enzyme immunoassays (EIA). C_T values at diagnosis and relevant clinical information were recorded. Receiver operating characteristic (ROC) curve was used to assess predictive validity and to find optimal C_T for CYT positive cases. Severity of CDI was assessed by blinded charts review.

RESULTS

Using CYT as the reference, ROC-derived Youden cut-off C_T of 28.0 predicted 77% cytotoxin positive cases, and 91% and 100% of severe and complicated CDI episodes respectively. The median C_T values for non-severe, severe, and complicated CDI episodes were 28.0, 24.5 and 22.5 respectively (p = 0.005).

CONCLUSIONS

Lower C_T value of the Xpert C. difficile PCR was associated with the presence of toxin and increased CDI severity. C_T values may be beneficial in interpreting positive C. difficile PCR results.

Point-Counterpoint: What Is the Optimal Approach for Detection of Clostridium difficile Infection?

INTRODUCTIONIn 2010, we published an initial Point-Counterpoint on the laboratory diagnosis of Clostridium difficile infection (CDI). At that time, nucleic acid amplification tests (NAATs) were just becoming commercially available, and the idea of algorithmic approaches to CDI was being explored. Now, there are numerous NAATs in the marketplace, and based on recent proficiency test surveys, they have become the predominant method used for CDI diagnosis in the United States. At the same time, there is a body of literature that suggests that NAATs lack clinical specificity and thus inflate CDI rates. Hospital administrators are taking note of institutional CDI rates because they are publicly reported. They have become an important metric impacting hospital safety ratings and value-based purchasing; hospitals may have millions of dollars of reimbursement at risk. In this Point-Counterpoint using a frequently asked question approach, Ferric Fang of the University of Washington, who has been a consistent advocate for a NAAT-only approach for CDI diagnosis, will discuss the value of a NAAT-only approach, while Christopher Polage of the University of California Davis and Mark Wilcox of Leeds University, Leeds, United Kingdom, each of whom has recently written important articles on the value of toxin detection in the diagnosis, will discuss the impact of toxin detection in CDI diagnosis.

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.

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.

Evaluation of the VIDAS glutamate dehydrogenase assay for the detection of Clostridium difficile

We evaluated the performance of the VIDAS GDH assay for the detection of Clostridium difficile. In total, 350 fecal specimens collected from patients clinically suspected of having CDI were analyzed by C. difficile culture and enzyme-linked fluorescent immunoassay (VIDAS GDH); the results were compared with those of toxigenic C. difficile culture (TC), PCR (Xpert C. difficile assay), and toxin AB EIA (VIDAS CDAB). The numbers of culture-positive and culture-negative samples were 108 and 242, respectively. The concordance between the GDH assay and C. difficile culture was 90.3%. With PCR, 12 more samples were found to be positive in GDH-positive/C. difficile culture-negative specimens. Thus, the concordance between GDH assay and C. difficile culture/PCR was 93.7%. The sensitivity, specificity, positive predictive value, and negative predictive value of the VIDAS GDH assay were 97.2%, 87.2%, 77.2%, and 98.6%, respectively, based on the C. difficile culture, and 97.5%, 91.7%, 86.0%, and 98.6%, respectively, based on C. difficile culture/PCR. Positivity rates of the GDH assay were partially associated with those of semi-quantitative C. difficile cultures, which were maximized in grade 3 (>100 colony-forming unit [CFU]) compared with grade 1 (<10 CFU). We evaluated the two-step or three-step algorithm using GDH assay as a first step. No toxin EIA-positive case was found among GDH-negative samples, and 60.8% (48/79) were TC- and/or PCR-positive among the GDH-positive/toxin EIA-negative samples. Thus, approximately 25% of the 350 samples required a confirmatory test (TC or PCR) in the GDH-toxin EIA algorithm, whereas only 2.3% of the total samples in GDH-PCR algorithm was discrepant and required another confirmatory test like TC.

The phenotypic legacy of admixture between modern humans and Neandertals

Many modern human genomes retain DNA inherited from interbreeding with archaic hominins, such as Neandertals, yet the influence of this admixture on human traits is largely unknown. We analyzed the contribution of common Neandertal variants to over 1000 electronic health record (EHR)-derived phenotypes in ~28,000 adults of European ancestry. We discovered and replicated associations of Neandertal alleles with neurological, psychiatric, immunological, and dermatological phenotypes. Neandertal alleles together explained a significant fraction of the variation in risk for depression and skin lesions resulting from sun exposure (actinic keratosis), and individual Neandertal alleles were significantly associated with specific human phenotypes, including hypercoagulation and tobacco use. Our results establish that archaic admixture influences disease risk in modern humans, provide hypotheses about the effects of hundreds of Neandertal haplotypes, and demonstrate the utility of EHR data in evolutionary analyses.

Clostridium difficile outbreak caused by NAP1/BI/027 strain and non-027 strains in a Mexican hospital

Background

Clostridium difficile infections caused by the NAP1/B1/027 strain are more severe, difficult to treat, and frequently associated with relapses.

Methods

A case–control study was designed to examine a C. difficile infection (CDI) outbreak over a 12-month period in a Mexican hospital. The diagnosis of toxigenic CDI was confirmed by real-time polymerase chain reaction, PCR (Cepheid Xpert C. difficile/Epi).

Results

During the study period, 288 adult patients were evaluated and 79 (27.4%) patients had confirmed CDI (PCR positive). C. difficile strain NAP1/B1/027 was identified in 31 (39%) of the patients with confirmed CDI (240 controls were included). Significant risk factors for CDI included any underlying disease (p < 0.001), prior hospitalization (p < 0.001), and antibiotic (p < 0.050) or steroid (p < 0.001) use. Laboratory abnormalities included leukocytosis (p < 0.001) and low serum albumin levels (p < 0.002). Attributable mortality was 5%. Relapses occurred in 10% of patients. Risk factors for C. difficile NAP1/B1/027 strain infections included prior use of quinolones (p < 0.03).

Risk factors for CDI caused by non-027 strains included chronic cardiac disease (p < 0.05), chronic renal disease (p < 0.009), and elevated serum creatinine levels (p < 0.003). Deaths and relapses were most frequent in the 027 group (10% and 19%, respectively).

Conclusions

C. difficile NAP1/BI/027 strain and non-027 strains are established pathogens in our hospital. Accordingly, surveillance of C. difficile infections is now part of our nosocomial prevention program.

A hospital-level cost-effectiveness analysis model for toxigenic Clostridium difficile detection algorithms

BACKGROUND

Despite thorough analyses of the analytical performance of Clostridium difficile tests and test algorithms, the financial impact at hospital level has not been well described. Such a model should take institution-specific variables into account, such as incidence, request behaviour and infection control policies.

AIM

To calculate the total hospital costs of different test algorithms, accounting for days on which infected patients with toxigenic strains were not isolated and therefore posed an infectious risk for new/secondary nosocomial infections.

METHODS

A mathematical algorithm was developed to gather the above parameters using data from seven Flemish hospital laboratories (Bilulu Microbiology Study Group) (number of tests, local prevalence and hospital hygiene measures). Measures of sensitivity and specificity for the evaluated tests were taken from the literature. List prices and costs of assays were provided by the manufacturer or the institutions. The calculated cost included reagent costs, personnel costs and the financial burden following due and undue isolations and antibiotic therapies. Five different test algorithms were compared.

FINDINGS AND CONCLUSION

A dynamic calculation model was constructed to evaluate the cost:benefit ratio of each algorithm for a set of institution- and time-dependent inputted variables (prevalence, cost fluctuations and test performances), making it possible to choose the most advantageous algorithm for its setting. A two-step test algorithm with concomitant glutamate dehydrogenase and toxin testing, followed by a rapid molecular assay was found to be the most cost-effective algorithm. This enabled resolution of almost all cases on the day of arrival, minimizing the number of unnecessary or missing isolations.

Evaluation of multiple real-time PCR tests on nasal samples in a large MRSA surveillance program

OBJECTIVES

We evaluated the LightCycler MRSA Advanced Test (Roche Molecular Diagnostics, Pleasanton, CA), the BD MAX MRSA assay (Becton Dickinson, Franklin Lakes, NJ), and the Xpert MRSA assay (Cepheid, Sunnyvale, CA) on nasal samples using the same population.

METHODS

Admission and discharge nasal swabs were collected from inpatients using a double-headed swab. One swab was plated onto CHROMagar MRSA (CMA; Becton Dickinson, Sparks, MD) and then broken off into tryptic soy broth (TSB) for enrichment. TSB was incubated for 24 hours and then plated to CMA. The molecular tests were performed on the second swab. We analyzed the cost benefit of testing to evaluate what parameters affect hospital resources.

RESULTS

A total of 27,647 specimens were enrolled. The sensitivity/specificity was 98.3%/98.9% for the LightCycler MRSA Advanced Test and 95.7%/98.8% for the Xpert MRSA assay, but the difference was not significant. The positive predictive value was 86.7% for the LightCycler MRSA Advanced Test, 82.7% for the Xpert MRSA assay (P > .1), and 72.2% and for the BD MAX MRSA test (P < .001 compared with the LightCycler MRSA Advanced Test). All three assays were cost-effective, with the LightCycler MRSA Advanced Test having the highest economic return.

CONCLUSIONS

Our results suggest that the performance of the three commercial assays is similar. When assessing economic cost benefit of methicillin-resistant Staphylococcus aureus screening, the two measures with the most impact are the cost of the test and the specificity of the assay results.

Evaluation of the illumigene C. difficile assay for toxigenic Clostridium difficile detection: a prospective study of 302 consecutive clinical fecal samples

Toxigenic Clostridium difficile is a major pathogen causing nosocomial diarrhea. Consequently, rapid detection of toxigenic C. difficile is very important in clinical laboratories. The illumigene C. difficile DNA amplification assay (illumigene; Meridian Bioscience, Inc.) is a rapid method that detects the toxin A gene (tcdA) by loop-mediated isothermal amplification. In the present study, we evaluated the diagnostic performance of the illumigene assay using 302 consecutive stool specimens in comparison with the VIDAS C. difficile A&B enzyme-linked fluorescent immunoassay (VIDAS-CDAB; bioMérieux). Toxigenic culture was used as the reference method. The sensitivity, specificity, positive predictive value, and negative predictive value of the illumigene assay were 88.1%, 96.7%, 86.7%, and 97.1%, respectively, while those of the VIDAS-CDAB assay were 40.4%, 98.8%, 87.5%, and 88.5%, respectively. It is of note that use of a combination of the illumigene and VIDAS-CDAB assays did not improve any of the 4 evaluated parameters (88.1%, 95.5%, 82.5%, and 97.1%, respectively). The illumigene assay showed limits of detection of 250 and 11,467 CFU/mL for ATCC 9688 (tcdA+, tcdB+, cdtB-) and ATCC 43598 (tcdA-, tcdB+, cdtB-) reference strains, respectively, and there was no cross-reactivity with 8 frequently isolated bacterial species. In conclusion, the illumigene assay might be a useful method for rapid detection of toxigenic C. difficile in clinical laboratories. Additionally, the VIDAS-CDAB assay seems unnecessary if the illumigene assay is used.

Comparison of the Verigene Clostridium difficile, Simplexa C. difficile Universal Direct, BD MAX Cdiff, and Xpert C. difficile assays for the detection of toxigenic C. difficile

We compared the Verigene Clostridium difficile test (Nanosphere, Northbrook, IL, USA), the Simplexa C. difficile Universal Direct (Focus Diagnostics, Cypress, CA, USA), the BD MAX Cdiff (Becton Dickinson, Franklin Lakes, NJ, USA), and the Xpert C. difficile (Cepheid, Sunnyvale, CA, USA) assays for the detection of toxigenic C. difficile. One hundred and ninety deidentified, remnant diarrheal specimens were included in this study. After resolution of discordant results by toxigenic culture, the Xpert C. difficile assay displayed the highest sensitivity (100%), with a specificity of 98.8%. The sensitivity and specificity were 95.2% and 99.4% and 87% and 100% for the Verigene CDF and Simplexa Universal Direct assays, respectively. Finally, the BD MAX assay showed a sensitivity of 87% and a specificity of 98.8%. Despite differences in the overall performance of these assays, these results support the routine use of these platforms for the detection of toxigenic C. difficile in the clinical laboratory.