Interpretation of Quick Test Results in Clostridium difficile Infection

Abstract

  Until recently, the kit used in our hospital to determine Clostridium difficile infection (CDI) detected only toxins A and B. However, we recently switched to a kit that detects both toxins and antigens, after production of the previously used kit was discontinued. Accordingly, hospital staff expected that the change in kits could lead to confusion in the clinical setting concerning the interpretation of “antigen-positive toxin-negative” cases. To investigate whether countermeasures for CDI should be implemented, culture tests were performed for antigen-positive toxin-negative cases and correlations with fever and increased inflammatory marker values were examined. Isolation cultures were performed for specimens obtained from 31 antigen-positive toxin-negative cases, examined using the new kit with the direct method in August and September 2012. The isolates were then retested using the same kit. The presence of diarrhea, fever, and increased inflammatory marker values was also surveyed. Diarrhea was observed in all 31 cases. The preparation of isolation cultures was successful in 24 of the 31 cases. Retesting of these cases gave positive results for toxins in 17 cases and negative results in seven cases. Fever was observed in 13 cases (76.5%) and increased inflammatory marker values were observed in 12 cases (70.6%) of the 17 toxin-positive cases on retesting. Of the remaining 14 cases (seven toxin-negative cases on retesting and seven unsuccessful isolation culture cases), fever was observed in six cases (42.9%) and increased inflammatory marker values were observed in six cases (42.9%). There were no significant differences between the two groups. However, the possibility of CDI cannot be excluded in antigen-positive toxin-negative cases exhibiting diarrhea, fever, and increased inflammatory marker values. Therefore, contact infection countermeasures should be implemented quickly and treatment initiation should be considered in such cases in the future, as is now applied for toxin-positive cases identified using the direct method.