Clostridioides (Clostridium) difficile

Clostridioides difficile (formerly known as Clostridium difficile) produces disease-causing toxins A and B and is the most common cause of healthcare-associated infection in adults in the United States and the most frequent cause of infectious diarrhea in clinical settings.   C. difficile infection (CDI) is defined as acute-onset diarrhea in the presence of toxigenic C. difficile or C. difficile toxins, with no other known cause for diarrhea.  Beginning in 2000, CDI increased in severity and incidence in both children and adults with the emergence of a more virulent strain known as ribotype 027 (also called NAP1 or BI).  The current estimated rate of CDI is approximately 500,000 cases per year, and transmission is typically person to person, through the fecal-oral route.   CDI severity has been defined in various ways on the basis of clinical findings, laboratory data, intensive care unit (ICU) stay, colectomy, and/or mortality.  The high prevalence of asymptomatic colonization, found in up to 5-50% of inpatients, complicates diagnosis, and controversy exists about whether diagnostic testing should focus on testing stool for toxins or for toxigenic C. difficile organisms.  Currently recommended tests include the nucleic acid amplification test (NAAT), stool toxin enzyme immunoassay (EIA), and glutamate dehydrogenase (GDH) test. 

Quick Answers for Clinicians

Who should be tested for Clostridioides difficile infection?

In general, adolescents and adults with Clostridioides difficile infection (CDI) risk factors and unexplained and new-onset diarrhea, with three or more loose (unformed) stools within 24 hours, warrant testing for CDI.  (Although rare, it is possible for patients with an ileus and complicated disease to have formed stool; see Laboratory Testing for the recommended approach in these cases. ) CDI testing is not recommended in neonates and infants because of the high prevalence of asymptomatic C. difficile colonization in this age group.  In toddler-age children, testing is only recommended once other infectious and noninfectious causes have been ruled out.  In children older than 2 years, persistent and worsening diarrhea in the presence of CDI risk factors should prompt testing. 

What are the risk factors for Clostridioides difficile infection?

Healthcare-facility exposure, particularly a long stay in a hospital or other medical facility, is a primary risk factor for Clostridioides difficile infection (CDI).  Additional risk factors include treatment with antibiotics or proton pump inhibitors, advanced age, and illnesses such as inflammatory bowel disease (IBD), chronic kidney disease, end-stage renal disease, and HIV.  Patients undergoing solid organ or hematopoietic stem cell transplantations, chemotherapy, gastrointestinal surgery, and tube feeding are also at increased risk, as are patients who have had CDI previously.  Although risk factors in children are similar to those in adults (mainly antibiotic use, hospitalization, organ transplantation, and chronic conditions such as IBD or cancer), an additional risk factor is the use of gastrostomy or jejunostomy tubes. 

Which tests should be used for Clostridioides difficile infection testing?

In patients who have symptoms and risk factors consistent with Clostridioides difficile infection (CDI), the Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA) recommend use of a nucleic acid amplification test (NAAT) alone, or a stool enzyme immunoassay (EIA) toxin test in combination with a glutamate dehydrogenase (GDH) test and/or NAAT.  In symptomatic patients with unclear risk factors for CDI (eg, suspected community-acquired infection), the stool toxin test should be used in conjunction with GDH and/or NAAT, but the NAAT alone is not recommended. 

Is repeat testing for Clostridioides difficile infection recommended?

The American College of Gastroenterology (ACG) discourages repeat testing for Clostridioides difficile infection (CDI) within 7 days during one episode of diarrhea.  Studies indicate that a nucleic acid amplification test (NAAT) repeated during a 7-day window has a low diagnostic yield (approximately 2%).  Exceptions to this recommendation are only advised in patients with high clinical suspicion, initial negative tests, and worsening or persistent symptoms in the context of an institutional epidemic of CDI.  The ACG also discourages tests of cure.  Enzyme immunoassay (EIA) and toxigenic culture tests for both toxins A and B may give positive results for up to 30 days in patients whose symptoms have resolved, so false-positive tests of cure may result in unnecessary or prolonged treatment.  

Which testing algorithms are related to this topic?

Indications for Testing

The Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA) recommend CDI testing be performed in those with CDI risk factors and unexplained and new-onset diarrhea, with three or more loose (unformed) stools within 24 hours.  In children older than 2 years, persistent and worsening diarrhea along with CDI risk factors is an indication for CDI testing, but the IDSA and SHEA recommend testing in toddler-age children only after other infectious/noninfectious causes have been ruled out.  CDI testing is not routinely recommended in neonates or infants. 

Laboratory Testing

Diagnosis

The American College of Gastroenterology (ACG) recommends that tests for CDI be performed on diarrheal stools only because of the high prevalence of asymptomatic colonization.  (Rarely, patients with an ileus and complicated disease may have formed stool; see Nucleic Acid Amplification. ) The IDSA and SHEA jointly recommend testing as described in the following table.  Individual institutional protocols for CDI diagnosis, if established, should be followed.

IDSA/SHEA-Recommended Testing Strategy for CDI
Symptomatic Patientsa with Risk Factors Strongly Consistent with CDIb Symptomatic Patientsa with Unclear Risk Factorsc for CDI

NAAT alone, or

Stool toxin EIA plus NAAT, or

Stool toxin EIA plus GDH, or

Stool toxin EIA plus GDH, plus NAAT if results are discordant

Stool toxin EIA plus GDH, or

Stool toxin EIA plus GDH, plus NAAT if results are discordant, or

Stool toxin EIA plus NAAT

aUnexplained and new-onset diarrhea, with ≥3 loose (unformed) stools within 24 hrs, and applicable clinical risk factors indicate greater likelihood of CDI.

bRisk factors for CDI include healthcare-facility exposure, particularly a long stay in a hospital or other medical facility, treatment with antibiotics or proton pump inhibitors, advanced age, and certain illnesses; see Quick Answers for Clinicians for a more comprehensive list of risk factors.

cUnclear risk factors might include suspected community-acquired infection, for example.

Source: McDonald, 2018 

Refer to Clostridioides difficile (Clostridium difficile) Infection Testing Algorithm.

Repeat testing and tests for cure are discouraged because patients can test positive for C. difficile even after the conclusion of effective treatment.  

Nucleic Acid Amplification

A NAAT such as polymerase chain reaction (PCR) to detect the C. difficile toxin B gene (tcdB) can be used as a single test in symptomatic patients with a high pretest probability of having CDI.  Because of its high sensitivity and inability to differentiate between colonization and disease, NAAT use is discouraged in asymptomatic patients who may be C. difficile carriers without infection.  In patients at risk for CDI but without symptoms, NAAT can be used in conjunction with stool toxin testing (EIA) or to confirm equivocal results of stool toxin and GDH tests. 

Although uncommon, it is possible for patients who have an ileus and complicated disease to have formed stool rather than diarrhea; in these cases, rectal swabs can be used for PCR testing. 

Combined Testing

Stool Toxin Tests

EIAs can be used to detect C. difficile toxins in stool, but available tests vary widely in sensitivity. The IDSA and SHEA recommend that only the higher sensitivity toxin EIA tests be offered in clinical laboratories.  Where offered, this testing should be performed in conjunction with GDH testing and/or NAAT. 

Glutamate Dehydrogenase Test

GDH is an enzyme produced by both toxigenic and nontoxigenic C. difficile.  An EIA can be used to detect GDH antigen. Although the GDH test is a rapid initial test, it detects only the presence of the C. difficile organism and not toxin production. It is also less sensitive than the tcdB PCR (NAAT).

Other Testing (Useful Only in Certain Situations)

Toxigenic Culture

Toxigenic culture (TC), formerly the gold standard test, involves the culturing of C. difficile from stool; cytotoxic assays are then used to test isolates for cytotoxin production.  This method can require ≥96 hours and has limited diagnostic utility.  Its results reflect toxin production in vitro, which may not correlate with toxin production in vivo. 

Cell Culture Cytotoxicity Assay

Another reference standard is the cell culture cytotoxic assay, which can detect toxins in stool filtrate.  This test can be used to identify cell rounding that is characteristic of cell exposure to toxins, and is more likely to detect toxin B than toxin A.  The cell culture cytotoxicity assay is qualitative, subjective, requires 24 to 48 hours for incubation, and is not widely used. 

Strain Typing

Strain typing can be useful for epidemiologic tracking, and a variety of methods, such as restriction endonuclease analysis (REA) typing and PCR ribotyping, are available.  Such methods can be used to identify new C. difficile strains and assess the relatedness of different strains. 

ARUP Laboratory Tests

Recommended Tests

NAAT (PCR)

Recommended rapid, stand-alone test for C. difficile infection in symptomatic patients

GDH antigen and toxin A/B testing with reflex to NAAT

Other Testing (Useful Only in Certain Situations)

Not the preferred initial test for diagnosis of C. difficile-associated diarrhea; results may take 2-5 days

Reference method for diagnosis of C. difficile-associated diarrhea; results may take ≥96 hours

Do not order for diagnosis of C. difficile-associated diarrhea; for research interest/epidemiologic purposes only

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories

References

Additional Resources
Resources from the ARUP Institute for Clinical and Experimental Pathology®