Comparison of four commercially available rapid enzyme immunoassays with cytotoxin assay for detection of Clostridium difficile toxin(s) from stool specimens.

Rapid (2.5- to 3.5-h) enzyme immunoassays (EIAs) for the detection of Clostridium difficile toxins have been developed. We report the results of simultaneous testing of 700 fresh stool specimens by the tissue culture cytotoxin assay and four EIAs (Bartels Prima System C. difficile Toxin A EIA, Cambridge Biotech Cytoclone A+B EIA, Meridian Diagnostics Premier C. difficile Toxin A EIA, and TechLab C. difficile Tox-A Test EIA). In cases of disagreement, culturing for toxigenic C. difficile was performed. A total of 61 (8.7%) specimens from 46 patients were positive for C. difficile toxin. The sensitivity of the cytotoxin assay was 87%, and that of culture was 93%. In comparison with the cytotoxin assay results, the sensitivity and specificity of the EIAs were as follows: Bartels, 87 and 96%; Cambridge, 89 and 99%; Meridian, 87 and 98%; and TechLab, 87 and 95%, respectively. In comparison with the cytotoxin assay plus toxigenic culture results, the sensitivity and specificity of the EIAs were as follows: Bartels, 84 and 97%; Cambridge, 85 and 99%; Meridian, 79 and 98%; and TechLab, 80 and 96%, respectively. The EIAs varied in positive predictive values (PPVs). A high PPV was seen with the Cambridge EIA (96%); lower PPVs were seen with the TechLab (64%), Bartels (72%), and Meridian (80%) EIAs because of high false-positive rates. The negative predictive values (98 to 99%) were excellent with all EIAs. Results were indeterminant with 0.3% of the samples by the Meridian EIA and 3% by all the other EIAs. Although the EIAs were less sensitive than the cytotoxin assay, they provide same-day results and may be useful in laboratories without tissue culture facilities.

Detection of herpes simplex virus by a nonradiometric spin-amplified in situ hybridization assay.

An in situ hybridization kit (Diagnostic Hybrids, Inc., Athens, Ohio) was evaluated for use in the detection and identification of herpes simplex virus (HSV) from clinical specimens. For in situ hybridization, a 10-min spin amplification onto monolayers of African green monkey kidney cells (CV-1) in 24-well polystyrene dishes, 24-h culture amplification, and hybridization with an alkaline phosphatase-labeled DNA probe were used. A total of 648 specimens were tested, including 275 specimens from patients with symptomatic diseases sent specifically for HSV detection and 373 specimens from asymptomatic immunocompromised patients sent for detection of HSV shedding. Overall, the sensitivity of the hybridization assay was 97.8% (131 of 134 specimens), with 105 of 105 (100%) specimens from symptomatic patients and 26 of 29 (89.9%) specimens from asymptomatic patients being detected. The three specimens that were false negative by in situ hybridization had low virus titers, as determined by tissue culture. The specificity was 99.6% (512 of 514 specimens). The rapid, accurate results suggest that the in situ hybridization kit may be used as an alternative to conventional tissue culture for the detection of HSV.

Recovery of Histoplasma capsulatum from blood in a commercial radiometric Mycobacterium medium.

We report the recovery of Histoplasma capsulatum from blood specimens cultured for Mycobacterium sp. in BACTEC 13A radiometric medium. H. capsulatum was recovered from six of eight blood specimens submitted for mycobacterial cultures from five human immunodeficiency virus-positive individuals. Initial positive metabolic signals occurred at a mean of 11 days, but no organisms were detected with acid-fast stains. The bottles remained positive, and after an additional incubation (mean, 8 days), yeast cells morphologically compatible with H. capsulatum were detected when aliquots were stained with acridine orange. Therefore, when radiometric mycobacterial blood cultures with persistent positive metabolic signals and negative acid-fast stains are encountered, acridine orange staining and subculturing for a variety of microorganisms, including fungi, e.g., H. capsulatum, should be considered.