Systematic assessment of culture review as a tool to assess errors in the clinical microbiology laboratory.

CONTEXT: Daily supervisory review is a common practice in microbiology laboratories; however, there are no publications describing errors corrected by this practice. OBJECTIVE: To determine (1) the correction rates for routinely reviewed positive cultures, (2) the correction rates for negative cultures, and (3) the types of corrections that are found, including the number with potential clinical significance. DESIGN: We prospectively assessed errors identified during culture report review for all positive (10-month period) and negative (1-month period) cultures at a single, university-based clinical microbiology laboratory in the United States. Errors were classified using predefined categories, and total and per category error rates were determined. A chi(2) test was used to assess significant differences between error rates. RESULTS: A total of 112,108 culture reports were examined; 914 reports required a total of 1043 corrections. Of 101,703 positive culture reports, 786 (0.8%) required 900 corrections, 302 (0.3%) of which were potentially clinically significant. Of 10,405 negative culture reports, 128 (1.2%) required 143 corrections, 5 (0.05%) of which were potentially clinically significant. The rate of potentially clinically significant errors was significantly higher among positive versus negative culture reports (P < .001). Errors from positive culture reports most commonly involved susceptibility (374 [42%]), reporting (275 [31%]), and identification workup (217 [24%]). Most potentially significant errors from positive culture reports involved susceptibility testing (n = 253) and specimens from wound or lower respiratory tract (P < .001). CONCLUSIONS: Review of culture reports from positive cultures from nonsterile sites with special attention to antimicrobial susceptibility testing and reporting would be most likely to detect potentially significant errors within the clinical microbiology laboratory.

Convenient selective differential broth for isolation of vancomycin-resistant enterococcus from fecal material.

Studies have shown that vancomycin broth enrichment is superior to direct plating for the detection of vancomycin-resistant enterococcus (VRE), but vancomycin selective broth is not generally commercially available. We developed an easy-to-prepare VRE selective differential broth and compared it to direct plating on bile esculin azide (BEA) agar for the isolation of VRE from fecal samples. A total of 528 consecutive rectal swabs and stools were inoculated onto BEA agar and into BEA broth with vancomycin at a concentration of 15 microg/ml (BEA VAN15 microg/ml broth). After 1 to 2 days of incubation, broths were subcultured to BEA VAN6 microg/ml agar. Bile esculin-positive colonies from the direct and broth subculture plates were evaluated for the presence of VRE by standard microbiological techniques. Addition of the broth enrichment step led to the detection of significantly more VRE isolates than did direct plating alone (28 versus 18 VRE isolates, respectively). In all, 30 VRE strains were isolated from 29 cultures, all of which were Enterococcus faecium. MICs of vancomycin ranged from 32 microg/ml (n = 2) to > 256 microg/ml (n = 28). Twenty-two VRE isolates were available for further testing: sixteen exhibited a VanA phenotype and six were of the VanB phenotype. van genotypes were in agreement with phenotypes for all VRE isolates except one, which could not be genotyped. The broth method also resulted in significantly fewer bile esculin-positive, non-VRE isolates requiring further workup. We have thus developed an easily prepared vancomycin selective differential broth that is significantly more sensitive and specific in the detection of VRE than is direct fecal plating to BEA agar.

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.