In a patient with watery, non-bloody diarrhea, which test is most likely to confirm the diagnosis of C. difficile infection?

In cases of suspected Clostridium difficile infection, the most effective diagnostic method involves evaluating the presence of toxins produced by the bacteria. The ELISA test for C. difficile-associated toxins A and B specifically detects these toxins, which are responsible for the pathophysiology of C. difficile infections. A positive result confirms active infection and supports the diagnosis, particularly in patients presenting with watery, non-bloody diarrhea, which is characteristic of this condition.

The other tests are not appropriate for directly diagnosing C. difficile infection in this scenario. For example, a Sudan stain for fecal fat is utilized to assess fat malabsorption conditions but does not provide information on C. difficile. Microscopic examination for ova and parasites is aimed at identifying intestinal parasitic infections, while the D-xylose test evaluates malabsorption but is irrelevant to a C. difficile diagnosis. Thus, using ELISA for toxins A and B is the most specific and relevant approach in confirming the presence of a C. difficile infection in patients with the outlined symptoms.