ABSTRACT
BACKGROUND: Healthcare providers who have access to tests at the point of care (POC) are increasingly requesting the same performance from the POC test as they expect from the laboratory. With the introduction of the cobas® Liat instrument, highly sensitive molecular diagnostic testing can be performed closer to the patient in CLIA-waived, POC settings. As more sensitive tests become available, there is concern regarding contamination of instrumentation owing to improper handling, mistakes made when processing, or environmental contamination. Recent concerns were raised when a nurse performed environmental surveillance for flu A/B by inserting a dry swab into the cobas Liat instrument and then ran it as a sample on the instrument, generating a positive result. This finding stimulated questions about the possibility of system contamination contributing to false-positive results, ultimately leading to the possibility of providing incorrect treatment to patients. METHODS: To assess the likelihood of system contamination contributing to the generation of false-positive results, in this study we contaminated a cobas Liat System with flu A/B-positive control material. The system contamination was then assessed by swabbing exposed surfaces. Following confirmed system contamination, negative control samples were processed to determine whether system contamination had an impact on the expected negative results. RESULTS: Instrument contamination was confirmed, and no detectable flu A/B signal was observed for any of the negative control tubes run immediately following confirmation of system contamination. CONCLUSION: Environmental contamination of the Liat instrument does not have an impact on the integrity of the result.
Subject(s)
Equipment Contamination , Influenza A virus/genetics , Influenza B virus/genetics , Influenza, Human/diagnosis , Influenza, Human/virology , Point-of-Care Testing , Polymerase Chain Reaction , Humans , Point-of-Care Systems/standards , Point-of-Care Testing/standards , Polymerase Chain Reaction/methods , Polymerase Chain Reaction/standards , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
OBJECTIVES: Health care-associated methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus (SA) infections are continuing problems. Rapidly determining the MRSA colonization status of a patient facilitates practice to reduce spread of MRSA clinical disease. Sensitive detection of all SA prior to surgery, followed by decolonization, can significantly reduce postoperative infection from this pathogen. Our goal was to validate a new automated assay for this testing. METHODS: We compared performance of the cobas MRSA/SA Test on the cobas 4800 System to direct and enriched chromogenic culture using nasal swabs collected from patients at six United States sites. RESULTS: Compared to direct and enriched culture, the sensitivity for MRSA and SA was 93.1% and 93.9%, and the specificity was 97.5% and 94.2%, respectively. After discrepancy analysis, the sensitivity for MRSA and SA was 97.1% and 98.6%, and the specificity was 98.3% and 95.5%, respectively. Compared to direct culture, sensitivity for detecting any SA was 99.6%. CONCLUSIONS: The cobas MRSA/SA Test is an effective tool to simultaneously perform surveillance testing for nasal colonization of both MRSA and MSSA.
Subject(s)
Bacteriological Techniques/methods , Nasal Cavity/microbiology , Staphylococcal Infections/diagnosis , Adolescent , Adult , Aged , Aged, 80 and over , DNA, Bacterial/analysis , DNA, Bacterial/isolation & purification , Female , Humans , Male , Methicillin-Resistant Staphylococcus aureus/isolation & purification , Middle Aged , Nasal Lavage Fluid/microbiology , Prevalence , Real-Time Polymerase Chain Reaction , Staphylococcal Infections/microbiology , Staphylococcus aureus/isolation & purification , Young AdultABSTRACT
Nucleic acid amplification tests (NAATs) are reliable tools for the detection of toxigenic Clostridium difficile from unformed (liquid or soft) stool samples. The objective of this study was to evaluate performance of the cobas Cdiff test on the cobas 4800 system using prospectively collected stool specimens from patients suspected of having C. difficile infection (CDI). The performance of the cobas Cdiff test was compared to the results of combined direct and broth-enriched toxigenic culture methods in a large, multicenter clinical trial. Additional discrepancy analysis was performed by using the Xpert C. difficile Epi test. Sample storage was evaluated by using contrived and fresh samples before and after storage at -20°C. Testing was performed on samples from 683 subjects (306 males and 377 females); 113 (16.5%) of 683 subjects were positive for toxigenic C. difficile by direct toxigenic culture, and 141 of 682 subjects were positive by using the combined direct and enriched toxigenic culture method (reference method), for a prevalence rate of 20.7%. The sensitivity and specificity of the cobas Cdiff test compared to the combined direct and enriched culture method were 92.9% (131/141; 95% confidence interval [CI], 87.4% to 96.1%) and 98.7% (534/541; 95% CI, 97.4% to 99.4%), respectively. Discrepancy analysis using results for retested samples from a second NAAT (Xpert C. difficile/Epi test; Cepheid, Sunnyvale, CA) found no false-negative and 4 false-positive cobas Cdiff test results. There was no difference in positive and negative results in comparisons of fresh and stored samples. These results support the use of the cobas Cdiff test as a robust aid in the diagnosis of CDI.
