Clostridium difficile (C. difficile) is a common cause of hospital-acquired infection, including an estimated 25% of cases of diarrhea that arise after use of antibiotics. In the United States, C. difficile causes approximately 300,000 hospital-acquired infections per year. Although some patients who are colonized by C. difficile have no symptoms, infection can cause diarrhea, high fever, severe abdominal pain, or perforation of the colon, which can prolong hospitalization and be life-threatening. Rapid and accurate diagnosis of this infection is essential for optimal management of infected patients, and for the prevention of nosocomial transmission. While the reference standards for diagnosis are highly accurate, i.e., the cell culture cytotoxicity assay, and toxigenic culture of isolates from stool samples, the relatively long turnaround time for test results is a downside, which has promoted research into rapid tests.