Repeat testing using the nucleic acid amplification test (within seven days) for C. difficile is not recommended when the symptoms represent a single episode of diarrheal illness. Studies have shown that repeat testing using the nucleic acid amplification test within a seven-day period yields only a 2% diagnostic yield. Exceptions should only be made in the setting of an institutional epidemic or when C. difficile infection is highly suspected with no alternative diagnosis, but for which the initial test is negative and symptoms persist or worsen.