Clostridium difficile PCR Cycle Threshold Predicts Free Toxin

摘要

Clostridium difficile is a cause of antibiotic-associated diarrhea (1). Laboratory assays employed to evaluate patients with suspected C. difficile infection (CDI) include enzyme immunoassay (EIA), which detects fecal free toxins (TcdA and TcdB), and PCR, which targets sequences encoding tcdA and/or tcdB (2). EIA glutamate dehydrogenase (GDH) is also used to detect C. difficile, but follow-up EIA toxin or PCR is needed to confirm toxigenicity. The best laboratory algorithm for diagnosing C. difficile infection (CDI) is debated (3). Compared to EIA toxin, PCR has a higher sensitivity for detection of toxigenic C. difficile in stool (4). However, studies suggest toxin positivity more accurately correlates with clinical outcomes compared with PCR (5–8). Polage and colleagues showed that patients with EIA toxin-negative (toxin?)/PCR-positive (PCR+) results had no CDI-related complications compared with EIA toxin+/PCR+ patients (7). These studies indicate that PCR is linked to overdiagnosis of patients colonized with C. difficile, triggering unnecessary antibiotic therapy. However, not all studies support this view (9–12). Some experts recommend using highly sensitive PCR to avoid missing toxin?/PCR+ CDI cases because EIA toxin is less sensitive compared with cell cytotoxicity neutralization assay (CCNA), which is the gold standard for fecal free toxin but takes several days to perform (3). To address these diagnostic challenges, European guidelines recommend a multistep testing algorithm starting with PCR or EIA GDH and followed by EIA toxin to rapidly identify toxin-positive and toxin?/PCR+ patients to facilitate appropriate clinical decision-making (4). Given the requirement for multistep testing, having a single stand-alone assay that can rapidly and sensitively detect toxigenic C. difficile and simultaneously predict free toxins would be valuable for guiding therapy and infection prevention practices.