Utility of two novel multiplexing assays for the detection of gastrointestinal pathogens - a first experience.

BACKGROUND: Cause for gastroenteritis range from viral, bacterial to parasitic pathogens. Rapid Multiplexing techniques like ProGastro_SSCS and xTAG_GPP can detect broad panels of pathogens simultaneously. We performed a field test with a total number of 347 stool samples from adult hospitalized patients that were tested with the Luminex xTAG GPP assay; of the 157 samples positively tested for at least one pathogen by xTAG GPP a total number of 30 samples was retested with the ProGastro SSCS assay. Assays were compared to standard routine diagnostics. FINDINGS: Multiplexing significantly reduced the time to the initial identification of a pathogen. Moreover, multiplexing detected pathogens for which a diagnostic assays was not requested by the physician and thus may be an important tool for avoiding nosocomial outbreaks. CONCLUSION: This first frontline approach with these assays approves their utility compared to conventional microbiological methods.

Comparison of two commercial PCR methods for methicillin-resistant Staphylococcus aureus (MRSA) screening in a tertiary care hospital.

Nose/throat-swabs from 1049 patients were screened for MRSA using CHROMagar MRSA, LightCycler Advanced MRSA, and Detect-Ready MRSA. Results were compared to the CHROMagar MRSA results, which was set as reference system. MRSA was detected in 3.05% of the patients with CHROMagar MRSA. LightCycler MRSA Advanced showed a higher clinical sensitivity (84.38%) than Detect-Ready MRSA (57.69%).The negative predictive values were high for both tests (>98%). The specificity and the positive predictive value were higher for the Detect-Ready MRSA test than for the LightCycler MRSA test (99.59% and 78.95% versus 98.52% and 64.29%). For routine screening LightCycler MRSA Advanced proved to be more efficient in our clinical setting as the clinical sensitivity was much higher than the sensitivity of Detect-Ready MRSA. CHROMagar MRSA detected more MRSA positive samples than both PCR methods, leading to the conclusion that the combination of PCR with cultural screening is still the most reliable way for the detection of MRSA. LightCycler MRSA Advanced was faster and needed less hands-on time. The advantage of Detect-Ready MRSA was the additional identification of methicillin-sensitive S.aureus (here in 34.63% of the samples), an information which can be possibly used for reducing the risk of postoperative infections in surgical patients in future.

Diagnosing toxigenic Clostridium difficile: new confidence bounds show culturing increases sensitivity of the toxin A/B enzyme immunoassay and refute gold standards.

OBJECTIVE: To scrutinize published sensitivity estimates obtained using questionable gold standards by comparing sensitivities of culturing Clostridium difficile in commercially available media followed by enzyme immunoassay (EIA) toxin A or B detection (culture test) with applying the EIA to stool samples alone (direct test). METHODS: In 2008, consecutive stool samples were cultured on C. difficile selective culture media: (1) medium I: Clostridium difficile-selective agar (CDSA; Becton Dickinson); (2) medium II: CLO agar (BioMérieux); (3) medium III: C. difficile agar according to Brazier (Oxoid). In addition, a direct test was performed (Ridascreen, r-Biopharm), which was also used to confirm toxin A or B production in the cultured C. difficile. New confidence bounds for sensitivities were applied, without assuming any perfect reference test or any conditional independence of the tests compared. RESULTS: Of 256 liquid stool samples, 18.4% were diagnosed as positive by at least 1 of the 4 tests; 12.8% were positive with culture medium I, 16.4% with medium II, and 13.6% with medium III, and 10.1% were positive by the direct test. Assuming culture tests to be at least as specific as the direct test yields an upper bound of 61% (upper 95% confidence bound (CB) 81%) for the sensitivity of the direct test. Assuming a prevalence of 15% yields sensitivity gains of the culture tests of at least 18% (lower 95% CB--4%) for medium I, 40% (lower 95% CB 21%) for medium II, and 23% (lower 95% CB 2%) for medium III. CONCLUSIONS: Published high sensitivities of direct toxin A/B EIAs, up to 96%, and the correctness of the cytotoxicity test assumed for their estimation are doubtful. With culture medium II, sensitivity gains of at least about 20% are obtainable. Direct toxin A/B EIAs alone are insufficiently sensitive for the clinical diagnosis of C. difficile infections.