Evaluation of Quantitative Hepatitis C Virus Core Antigen Testing as a Tool for Screening and Confirmation of HCV Infection.

BACKGROUND: Hepatitis C is a common viral infection worldwide. Finding the most effective diagnostic methods with low cost is always needed for laboratory improvement. In this study, we evaluated the performance of a quantitative chemiluminescent hepatitis C virus core antigen (HCV cAg) test by comparing it with the HCV confirmatory antibody line immunoblot assay (HCV Ab-LIA) test as well as the HCV quantitate reverse transcription-polymerase chain reaction (qRT-PCR) test. METHODS: A total of 394 samples were enrolled in the retrospective study. Of these, 225 samples were tested using HCV Ab screening and confirmatory Ab-LIA along with chemiluminescent HCV core Ag testing, while 169 samples were tested using qRT-PCR for HCV RNA and chemiluminescent HCV core Ag testing. RESULTS: Out of these, 225 positive samples tested by HCV Ab screening test were analyzed using the confirmatory Ab LIA and HCV cAg assays, a total of 183 samples (81.3 %) were confirmed to be Ab-positive, and among those, 77 samples (42.1%) were also positive for HCV cAg. Thirty-eight samples (20.76%) were HCV Ab indeterminate, and all of them were HCV cAg negative. Four samples (1.8%) were HCV Ab LIA-negative and negative for HCV cAg. Moreover, 169 samples were measured for qRT-PCR HCV viral load and quantitative HCV cAg test. One hundred and three samples were positive for HCV RNA, while 66 were negative. Among the positives, 96/103 samples were HCV cAg positive and 7/103 samples were negative. Out of the negatives, 4/66 samples were HCV cAg positive but 62/66 samples were negative. The HCV cAg results were concordant with the qRT-PCR results in 158 samples (93.5%); however, 11 samples (6.5%) were found to be discrepant. The sensitivity, specificity, positive predictive value, and negative predictive value of the quantitative HCV cAg were found to be 93%, 94%, 96%, and 90%, respectively. The overall coefficient of correlation between the HCV RNA levels and HCV cAg data was determined to be r2 = 0.9. CONCLUSIONS: The HCV cAg test showed a high correlation with the HCV RNA levels and may potentially be used as a more cost-effective alternative to the HCV RNA qRT-PCR test.

Methicillin-resistant Staphylococcus aureus replication in the presence of high (≥32 µg/ml) drug concentration of vancomycin as seen by electron microscopy.

Methicillin-resistant Staphylococcus aureus (MRSA) has unfortunately become a common pathogen in many healthcare facilities. In many institutions, vancomycin remains the preferred agent for treating serious MRSA infections including bacteraemia with or without endocarditis. The mutant prevention concentration (MPC) testing ≥109 colony forming units of bacteria, describes the antimicrobial drug concentration blocking the growth of the least susceptible cell from high density bacterial populations. With blood culture isolates of MRSA, we discovered strains with MPC values ≥32 µg/ml and viable cells could be readily recovered from agar plates containing 32 µg/ml of vancomycin. To investigate MRSA strains surviving in high concentrations of vancomycin on drug containing agar plates, we utilized electron microscopy to measure cell wall thickness as this has been previously reported as a potential mechanism of resistance1 along with septum thickening. Our data shows MRSA replication from high density bacterial populations in the presence of ≥32 µg/ml of vancomycin. Such observations may explain vancomycin failure in some patients and/or persistent bacteraemia and could potentially question the use of this drug in some critically ill patients in favour of an alternative agent.