Tag Archives: Clostridium difficile testing

New Study Evaluated Rectal Swabs For Clostridium difficile Testing

Clostridium difficile (C. diff) is among one of the top 18-drug-resistant threats to the United States according to the Centers for Disease Control and Prevention, responsible for around 250,000 infections on an annual basis and 14,000 deaths.

When it comes to diagnosis, microbiological testing of stool samples is often used. However, a new study suggests that for simple PCR-based detection of C. diff, dry rectal swabs were an effective substitute for the use of stool samples.

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“With this study, we proved that rectal swabs for the diagnosis of C. diff infection by PCR can replace the actually used stool samples,” study author Nathalie Jazmati, MD, University Hospital of Cologne, told our sister publication MD Magazine. “That will be more convenient for both patients and health care workers. Nevertheless, this was only a small study and our results have to be confirmed in a bigger clinical trial.”

In an effort to examine methods other than the analysis of stool specimens for C. diff confirmation, a research team from Germany examined the way rectal swabs with liquid transport medium and nylon flocked dry swabs performed for the detection of C. diff; they also evaluated the impact of storage temperature on the swabs.

For their study, the researchers collected 60 clinical stool samples that tested positive for C. diff by PCR and used them to simulate rectal swabs. Then, researchers dipped both wet and dry swabs into the stool and tested by PCR 3 times.

The first test took place immediately after the simulation “swab,” then, after 1 month and 3 months storage at -80°C. When the researchers tested the frozen samples, they first thawed them at room temperature for 15 minutes and the liquid swabs were vortexed for 30 seconds.

Testing all of the dry swabs 100% successfully detected C. diff, an equal rate of the stool sample testing; this proved true for all 3 phases of testing, and the researchers learned that no significant differences were found on the samples after they were frozen and thawed.

The detection rate for the other 30 liquid swabs was lower, at 83.2% accuracy. However, the researchers determined the temperature and the freezing and thawing of these samples did not have any significant impact.

The authors added that their results fall in line with other studies that tested PCR from rectal swabs in the detection of C. diff. The idea of using rectal swabs instead of stool samples isn’t new—it dates back to 1987.

Liquid swabs are currently cleared by the US Food and Drug Administration (FDA) for transport and the culture of gastrointestinal pathogens, the study authors continued, but it is not FDA approved for use with any molecular gastrointestinal assays.

In the future, dry swabs would “be appropriate and can probably speed up and facilitate the diagnosis of C. diff infection,” the researchers wrote, but warned, “nevertheless, using single step PCR-based detection of C. diff may lead to overdiagnosis of C. diff infection due to the high sensitivity but lower specificity of PCR.”

That marks a heightened importance for the careful clinical evaluation of the patient: Are they an asymptomatic carrier? Is there another reason for the patient’s diarrhea? Do they truly have a C. diff infection? All important questions to continue to ask.

While liquid swabs cannot substitute for the two-step laboratory diagnosis of C. diff, the researchers believe that their study shows the dry swab is a suitable alternative to stool sample testing.

Singulex, An Immunodiagnostics Company at the Forefront of Single Molecule Counting Technology

Singulex, an immunodiagnostics company at the forefront of Single Molecule Counting technology, a novel immunoassay technology recognized for unprecedented ultrasensitivity in the precision measurement of biomarkers, today announced that the company will present three posters, including one in collaboration with Stanford University, related to its investigational Singulex Clarity C. diff toxins A/B assay at the European Congress of Clinical Microbiology and Infectious Diseases.

Findings demonstrate the ultrasensitive Singulex Clarity C. diff toxins A/B assay, for use on the Singulex Clarity system, offers rapid results and a high level of sensitivity and specificity for the detection of Clostridium difficile toxins A and B in stool compared with currently available testing options. The Singulex Clarity system is a fully-automated, in vitro diagnostics platform powered by Single Molecule Counting technology. With up to 1000 times higher sensitivity than existing technologies, Single Molecule Counting reveals the presence or absence of disease more clearly and definitively than possible before.

“Commercially available tests used to diagnose C. difficile infection lack either in sensitivity or specificity,” said Niaz Banaei, Associate Professor of Pathology and Medicine (Infectious Diseases) at the Stanford University Medical Center and primary investigator of one study (poster #2881). “Data show that this new, rapid, standalone immunoassay addresses these shortcomings by detecting nearly all cell cytotoxicity neutralization assay (CCNA)-positive samples. The Singulex assay offers clinicians a new tool for accurate diagnosis of C. difficile infection.”

The Singulex Clarity C. diff toxins A/B assay, powered by Single Molecule Counting, aims to be the first ultrasensitive test to offer physicians and laboratorians the specificity intrinsic to toxin tests but at a sensitivity level that rivals molecular methods.

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ROCHE cobas® C. diff. Test approved by US Food and Drug Administration (FDA)

US Food and Drug Administration (FDA) has provided 510(k) clearance for the cobas® Cdiff Test to detect Clostridium difficile (C. difficile) in stool specimens.

The cobas® Cdiff Test targets the toxin B gene found in toxigenic C. difficile strains directly in specimens from symptomatic patients. The test provides accurate information which assists clinicians in making timely treatment decisions and aids in the prevention of further infection in healthcare settings.

“Having the ability to provide a result quickly is important when supporting infection control for Clostridium difficile,” said Dr. Steve Young, Professor of Pathology, Department of Pathology UNMHSC and Tricore Reference Lab. “The cobas® 4800 System has the capability to allow for mixed batch testing of the cobas® Cdiff Test alongside testing for Methicillin-resistant Staphylococcus aureus, Staphylococcus aureus, and herpes simplex virus 1 and 2*, all on one platform. We can run these assays together at least once in each shift rather than once a day, which can greatly improve laboratory efficiency, ultimately leading to better infection control and patient care.”

In a clinical trial program conducted at sites throughout the United States, the cobas® Cdiff Test demonstrated excellent performance compared to direct and enrichment toxigenic culture. The test combines high assay sensitivity with rapid turnaround time and a minimum number of pre-analytic steps, to facilitate earlier intervention of patients suffering from

C. difficile-associated disease. Earlier intervention can also lead to more effective implementation of infection control measures, which can prevent further transmission to additional patients.

About the cobas® 4800 System
The cobas® 4800 System offers true walk-away automation of nucleic acid purification, PCR set-up and real-time PCR amplification and detection to help laboratories achieve maximum efficiency. The expanding system menu in the U.S. currently includes the cobas® MRSA/SA Test, cobas® CT/NG Test (Chlamydia trachomatis/Neisseria gonorrhoeae), cobas® HPV Test, cobas® BRAF V600 Mutation Test, cobas® EGFR Mutation Test and cobas® KRAS Mutation Test.

“With the addition of the cobas® Cdiff Test to the cobas® 4800 System menu, Roche is able to expand the tools available to assist clinicians in the management of healthcare associated infections,” said Paul Brown, head of Roche Molecular Diagnostics. “The cobas® Cdiff Test requires less sample handling and provides laboratories with a simplified workflow, when compared to other molecular methods. It also delivers a lower inhibition rate, which means fewer repeat samples and chances for error, enabling better patient care.”


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Clostridium difficile (C.diff.) Testing Development and Validation of an Internationally-Standardized, High-Resolution Capillary Gel-Based Electrophoresis PCR-Ribotyping Protocol



PCR-ribotyping has been adopted in many laboratories as the method of choice for C. difficile typing and surveillance. However, issues with the conventional agarose gel-based technique, including inter-laboratory variation and interpretation of banding patterns have impeded progress.

The method has recently been adapted to incorporate high-resolution capillary gel-based electrophoresis (CE-ribotyping), so improving discrimination, accuracy and reproducibility.

However, reports to date have all represented single-center studies and inter-laboratory variability has not been formally measured or assessed.

Here, we achieved in a multi-center setting a high level of reproducibility, accuracy and portability associated with a consensus CE-ribotyping protocol. Local databases were built at four participating laboratories using a distributed set of 70 known PCR-ribotypes.

A panel of 50 isolates and 60 electronic profiles (blinded and randomized) were distributed to each testing center for PCR-ribotype identification based on local databases generated using the standard set of 70 PCR-ribotypes, and the performance of the consensus protocol assessed.

A maximum standard deviation of only ±3.8bp was recorded in individual fragment sizes, and PCR-ribotypes from 98.2% of anonymised strains were successfully discriminated across four ribotyping centers spanning Europe and North America (98.8% after analyzing discrepancies). Consensus CE-ribotyping increases comparability of typing data between centers and thereby facilitates the rapid and accurate transfer of standardized typing data to support future national and international C. difficile surveillance programs.


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Clostridium difficile toxin lab tests




Clostridium difficile toxin tests are used to diagnose antibiotic-associated diarrhea caused by toxin-producing C. difficile.

There are a number of tests available to detect the infection and to determine if the strain that is present produces toxin. Some tests are very sensitive and can take days to receive results. Other tests are rapid (several hours) and are not considered to be very sensitive.  Therefore, utilizing a combination of tests may be used to help make a diagnosis.

Commonly used tests include:

  • C. difficile toxin B, or toxins A and B, by enzyme immunoassay (EIA) tests are some of the most common tests used by laboratories. Results are typically available within 1 to 4 hours. Though these tests are rapid and widely available, they are not sensitive enough to detect many infections; they miss up to 30% of cases. Therefore, they are not recommended for use by some professional organizations.
  • A glutamate dehydrogenase (GDH) test detects an antigen that is produced in high amounts by C. difficile, both toxin and non-toxin producing strains. It may be used as a first step to rule out an infection with C. difficile, but it should not be used alone. Since it is not very specific for toxin-producing C. difficile, it is often used in combination with a test for toxin by EIA or a cytotoxicity culture.
  • Tissue culture to detect the C. difficile toxin is a test that looks for the effects of the cytotoxin on human cells grown in culture. It is a more sensitive testing method to detect toxin, but it requires 24 to 48 hours to get the test result.
  • A relatively new molecular PCR (polymerase chain reaction) lab test can rapidly detect the     C. difficile toxin B gene (tcdB) in a stool sample. This test is sensitive but is not widely available.
  • Toxigenic stool culture, which requires growing the bacteria in a culture and detecting the presence of the toxins, is the most sensitive test for C. difficile, and it is still considered to be the gold standard. This test does take 2 to 3 days for results.  * A culture will not distinguish between C. difficile  colonization and overgrowth/infection.

* Currently, there is not one test that is rapid, widely available, and sufficiently sensitive and specific.

Until the development of such a test, the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA) recommend a two-step testing process:

  • Perform an initial screen on stool samples using a test for glutamate dehydrogenase (GDH). This test is considered to be very sensitive.
  • Follow up positive screening results with a specific test for the toxin or the gene that codes for the toxin.

When are lab tests ordered?

Tests for C. difficile toxin may be ordered when an individual has symptoms such as: frequent watery stools (diarrhea) , abdominal pain, fever, and/or nausea during or has been treated with a course of antibiotics recently or over the past 6-8 weeks, or following a recent gastrointestinal surgery, several days after chemotherapy, or when a person has a chronic gastrointestinal disorder that the Physician./Healthcare professional suspects is being worsened by a C. difficile infection.

Tests for C. difficile toxin may be ordered to help diagnose the cause of diarrhea when no other discernible cause, such as parasites or pathogenic bacteria, has been detected from other lab tests.

When an individual is treated for antibiotic-associated diarrhea or colitis relapses and symptoms return, C. difficile toxin testing may be ordered to confirm the presence of the toxin.

Testing should not be ordered to monitor the effectiveness of treatment or on those who are symptomatic.      *  A reduction of symptoms associated with C. difficile, such as if diarrhea ceases and stools are formed, indicates a cure from infection.

**  Physicians and healthcare professionals may order lab testing at their own discretion **


Test results:

If tests for C. difficile toxin are positive, it is likely that the person’s diarrhea and related symptoms are due to an overgrowth of toxin-producing C. difficile.

Negative test results, with symptoms present, may mean that the diarrhea and other symptoms are being caused by something other than C. difficile  (Physicians may advise further testing).

Since the C. difficile toxin breaks down at room temperature within 2 hours, a negative result may also indicate that the sample was not transported, stored, or processed promptly.

* *  If there is a concern that a stool specimen has not been collected and processed properly, a repeat test may be ordered and performed.