Shin Bo-Moon, Kuak Eun Young, Lee Eun Joo, Songer J Glenn
Department of Laboratory Medicine, Sanggye Paik Hospital, Inje University, Seoul, South Korea.
J Clin Microbiol. 2009 Sep;47(9):2952-6. doi: 10.1128/JCM.00609-09. Epub 2009 Jul 22.
Enzyme immunoassays (EIA) to detect glutamate dehydrogenase or toxins A (TcdA) and B (TcdB), a cytotoxicity assay, and bacteriologic culture have disadvantages when applied individually to diagnosis of Clostridium difficile infections. Stool specimens (n = 1,596) were subjected to toxin detection via an enzyme-linked fluorescent immunoassay (ELFA; Vidas CDAB assay) and bacteriologic culture for toxigenic C. difficile in a three-step algorithm with additional toxigenic culture. Isolates (n = 163) from ELFA-negative stool specimens were examined via ELFA for toxin production. We amplified tcdA and tcdB from C. difficile isolates and tcdB from stool specimens that were ELFA positive or equivocal and culture negative, and we compared the results to those obtained with the three-step algorithm. More than 26% of stool specimens (419/1,596) were culture positive, yielding 248 isolates (59.2%) with both toxin genes (tcdA- and tcdB-positive isolates), 88 isolates (21.0%) with either tcdA or tcdB, and 83 (19.8%) that had no toxin genes (tcdA- and tcdB-negative isolates). Among 49 (culture-negative/ELFA-positive or -equivocal) stool specimens, 53.1% (26/49) represented tcdB-positive isolates. Therefore, the total number of PCR-positive cases was 362, and 27.1% (98/362) of these were detected through toxigenic culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 63.3%, 96.7%, 90.5%, and 92.4% (ELFA alone); 92.8%, 93.3%, 80.2%, and 97.8% (culture); and 70.7%, 91.4%, 95.5%, and 100% (three-step algorithm ELFA and bacterial culture with toxigenic culture), respectively, with culture and PCR for tcdA and tcdB as the standards. Thus, sensitivity and specificity were highest using culture and ELFA, respectively, but we recommend the three-step algorithm comprising EIA to detect both toxins and toxigenic culture for C. difficile as a practical method for achieving better PPV and NPV.
酶免疫测定法（EIA）用于检测谷氨酸脱氢酶或毒素A（TcdA）和毒素B（TcdB），细胞毒性测定法以及细菌培养法在单独应用于艰难梭菌感染的诊断时均存在不足之处。对1596份粪便标本采用三步算法进行检测，通过酶联荧光免疫测定法（ELFA；Vidas CDAB检测法）进行毒素检测，并对产毒艰难梭菌进行细菌培养，同时进行额外的产毒培养。对ELFA阴性粪便标本中的分离株（n = 163）通过ELFA检测其毒素产生情况。我们从艰难梭菌分离株中扩增tcdA和tcdB，从ELFA阳性或疑似阳性且培养阴性的粪便标本中扩增tcdB，并将结果与三步算法的结果进行比较。超过26%的粪便标本（419/1596）培养呈阳性，得到248株分离株（59.2%）同时具有两种毒素基因（tcdA和tcdB阳性分离株），88株分离株（21.0%）具有tcdA或tcdB中的一种，83株（19.8%）没有毒素基因（tcdA和tcdB阴性分离株）。在49份（培养阴性/ELFA阳性或疑似阳性）粪便标本中，53.1%（26/49）为tcdB阳性分离株。因此，PCR阳性病例总数为362例，其中27.1%（98/362）通过产毒培养检测到。以tcdA和tcdB的培养及PCR结果为标准，单独ELFA检测的敏感性、特异性、阳性预测值（PPV）和阴性预测值（NPV）分别为63.3%、96.7%、90.5%和92.4%；培养法的分别为92.8%、93.3%、80.2%和97.8%；三步算法（ELFA和产毒培养的细菌培养法）的分别为70.7%、91.4%、95.5%和100%。因此，培养法的敏感性最高，ELFA的特异性最高，但我们推荐采用包括检测两种毒素的EIA和艰难梭菌产毒培养的三步算法，作为一种能获得更好PPV和NPV的实用方法。
