Clinical correlation of toxin and common antigen enzyme immunoassay testing in patients with Clostridium difficile disease.

OBJECTIVE: The aim of the present study was to assess the correlation of Triage Micro Clostridium difficile Panel and toxin B cytotoxicity assay with the clinical diagnosis of C. difficile diarrhea. METHODS: The subjects evaluated were 98 patients with diarrhea for whom stool was submitted for testing for C. difficile. Clinical symptoms prompting evaluation, laboratory values, comorbid illness, and treatment outcomes that provided clinical insight into the etiology of the diarrhea were recorded. These data were then reviewed by two experienced clinical gastroenterologists who were blinded to the results of the Triage enzyme immunoassay and cytotoxin B assay. The final diagnosis of C. difficile diarrhea was based on the patient's clinical evaluation and symptoms, treatment, and subsequent outcome. RESULTS: Of 98 patients evaluated, 33 were diagnosed with C. difficile diarrhea by clinical criteria. The toxin B assay displayed 88% sensitivity and 100% specificity and positive predictive value. The toxin A component of the Triage Panel displayed 45% sensitivity but 98% specificity and 94% positive predictive value. The common antigen had 97% sensitivity and 95% negative predictive value. Among the 45 patients with only a common antigen detected, the most common diagnoses for diarrhea were chemotherapy-related, antibiotic-related diarrhea, and graft versus host disease. CONCLUSIONS: Our data show that both the Triage Micro C. difficile Panel and cytotoxin B for C. difficile have a high positive predictive value and negative predictive value for C. difficile diarrhea. The Triage Micro C. difficile Panel provides a reasonable alternative to the cytotoxin B assay in the assessment of clinically relevant C. difficile. The Triage Micro C. difficile Panel is less labor intensive and less expensive than cytotoxin B assay. The panel approach improves on the individual assay performances by increasing sensitivity and negative predictive value. When both common antigen and toxin A are positive, the likelihood of C. difficile diarrhea is high; conversely, when both results are negative, the likelihood of C. difficile diarrhea is low.

Six rapid tests for direct detection of Clostridium difficile and its toxins in fecal samples compared with the fibroblast cytotoxicity assay.

Clostridium difficile is one of the most frequent causes of nosocomial gastrointestinal disease. Risk factors include prior antibiotic therapy, bowel surgery, and the immunocompromised state. Direct fecal analysis for C. difficile toxin B by tissue culture cytotoxin B assay (CBA), while only 60 to 85% sensitive overall, is a common laboratory method. We have used 1,003 consecutive, nonduplicate fecal samples to compare six commercially available immunoassays (IA) for C. difficile detection with CBA: Prima System Clostridium difficile Tox A and VIDAS Clostridium difficile Tox A II, which detect C. difficile toxin A; Premier Cytoclone A/B and Techlab Clostridium difficile Tox A/B, which detect toxins A and B; and ImmunoCard Clostridium difficile and Triage Micro C. difficile panels, which detect toxin A and a species-specific antigen. For all tests, Triage antigen was most sensitive (89.1%; negative predictive value [NPV] = 98.7%) while ImmunoCard was most specific (99.7%; positive predictive value [PPV] = 95.0%). For toxin tests only, Prima System had the highest sensitivity (82.2%; NPV = 98.0%) while ImmunoCard had the highest specificity (99.7%; PPV = 95.0%). Hematopoietic stem cell transplant (HSCT) patients contributed 44.7% of all samples tested, and no significant differences in sensitivity or specificity were noted between HSCT and non-HSCT patients. IAs, while not as sensitive as direct fecal CBA, produce reasonable predictive values, especially when both antigen and toxin are detected. They also offer significant advantages over CBA in terms of turnaround time and ease of use.

Bordetella pertussis PCR: simultaneous targeting of signature sequences.

The absence of analytical controls for polymerase chain reaction (PCR)-based diagnostic tests for Bordetella pertussis limits their clinical utility. In this study, multiplex PCR simultaneously targeted two specific Bordetella pertussis sequences, the chromosomal repeated insertion sequence IS481 (IS) and the pertussis toxin promoter region (PT). A multi-target hybridization-EIA (Hyb-EIA) method in a 96-well microtiter-plate format was used to detect amplicons. Forty-seven (15%) of the 318 nasopharygeal specimens tested positive for at least one DNA target of B. pertussis by PCR, including the 10 known positive samples by culture and/or direct fluorescent antibody (DFA). Forty-six of the 47 PCR positive samples were considered positive for B. pertussis using the consensus interpretation criteria. Simultaneous detection of multiple chromosomal regions may identify false-positive and -negative results due to analytical variations or potential sequence polymorphism, and uncover a wider range of pathogenic strains.