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
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. 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. (Although rare, it is possible for patients with an ileus and complicated disease to have formed stool; see Laboratory Testing for recommendation for these cases. )
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.
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.
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.
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, and CDI testing is not routinely recommended in neonates or infants.
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 below. ) The IDSA and SHEA jointly recommend testing as described in the table below. Individual institutional protocols for CDI diagnosis, if established, should be followed.
|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 more comprehensive list of risk factors.
cUnclear risk factors might include suspected community-acquired infection, for example.
Test for Symptomatic Patients
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, its use is discouraged in asymptomatic patients who may be C. difficile carriers but 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.
Stool Toxin Tests
EIAs can be used to detect C. difficile toxins in stool, but available tests vary widely in sensitivity. It has been recommended 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 does not detect toxin production, only the presence of the C. difficile organism. It is also less sensitive than the tcdB PCR (NAAT).
Other Testing (Useful Only in Certain Situations)
The former gold standard test, toxigenic culture (TC) 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 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
Nucleic acid amplification test (PCR)
Recommended rapid, stand-alone test for C. difficile infection in symptomatic patients
Qualitative Polymerase Chain Reaction
GDH antigen and toxin A/B testing with reflex to NAAT
Qualitative Enzyme Immunoassay/Qualitative Polymerase Chain Reaction
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
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