No laboratory test can diagnose Clostridium difficile infection (CDI). Rather, CDI is a clinical diagnosis that can be supported by laboratory data. While a diagnostic assay may indicate the absence or presence of the organism or its toxins, the test by itself does not determine who does or does not have CDI.
One of the challenges in diagnosing CDI is that there are more asymptomatic C difficile carriers than there are people with CDI in the community and in the hospital. It is estimated 3% to 7% of the healthy adult population are colonized with C difficile.1 Asymptomatic colonization is more common among individuals with inpatient health care exposures. Between 4.4% and 15% of people are colonized with C difficile on admission to the hospital, with as many as 50% of persons living in long-term care facilities colonized.1 To add to the dilemma, diarrhea is frequent among those with health care exposures. Although C difficile is the most common health care–associated pathogen in the United States and CDI is a major cause of morbidity and mortality, it typically affects less than 1% of hospitalized patients and is the cause of diarrhea in only 5% to 10% of hospitalized people who have diarrhea and are tested for C difficile.1
Dubberke ER, Burnham CD. Diagnosis of Clostridium difficile InfectionTreat the Patient, Not the Test. JAMA Intern Med. 2015;175(11):1801–1802. doi:10.1001/jamainternmed.2015.4607