The 2017 IDSA/SHEA Guidelines Underscore the Importance of Accurate C. difficile Diagnosis.
Toxin genes in toxigenic C. difficile may be unexpressed. Patients colonized with these strains of C. difficile may be carriers. If toxin is not present, these patients likely do not have CDI and should not be treated.
Colonized C. difficile carriers are 5-10 times more common than patients with active infections in hospitals. When performed alone, Nucleic Acid Amplification Testing (NAAT) will identify carriers, who do not have CDI as well as active infections as positive because molecular tests only detect the toxin gene, not the toxin itself.4 A positive toxin result is necessary to define clinical disease.4-6
Misdiagnosis of CDI in carriers, who may have diarrhea from other causes, can lead to ineffective treatment and increases the risk to the patient of developing true C. difficile diarrhea.7,8 Hence, the new 2017 IDSA/SHEA guidelines recommend algorithm testing that includes glutamate dehydrogenase (GDH) antigen or NAAT as well as a toxin test to confirm active disease, as the method with the highest PPV for detecting CDI.9