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Hepatitis C virus (HCV) has been associated with acute and chronic posttransfusion and with sporadic non-A non-B (NANB) hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Cloning of the sequence encoding an antigenic component of HCV in 1989 led to the development of tests to detect antibody to HCV in serum. Viral HCV RNA can be detected and estimated with polymerase chain reaction (PCR) and branched-chain DNA (bDNA) signal amplification tests. The entire viral genome has been sequenced. The HCV envelope region varies considerably, and infections with mutant HCV have been described. Approximately 0.5-1.5% of healthy blood donors test positive, and HCV infection can be acquired by blood transfusion or i.v. drug abuse. Vertical and sexual transmission of the virus is rare, and the transmission mode remains obscure in a large group of patients. Acute hepatitis C is mild and often asymptomatic. Chronic hepatitis C has an indolent course but may progress to cirrhosis and HCC. Recombinant alpha interferon (IF) is used to treat chronic HCV disease, but no consensus has been reached on patient selection, dose, and duration of treatment. Approximately 50% of treated patients respond, but 50-80% of responders relapse over time. Liver transplantation in patients with end-stage, HCV-related liver disease is often followed by allograft infection. Short-term survival with reinfection is good, but the long-term consequences remain to be defined.

Introduction: Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is diagnosed by molecular-based detection of SARS-CoV-2 RNA. Serologic testing detects antibodies specific to SARS-CoV-2 and IgM specifically may serve as an adjunct test to PCR early in disease. We evaluated the Abbott anti-SARS-CoV-2 IgM and IgG assays along with DiaSorin anti-SARS-CoV-2 IgG and Roche anti-SARS-CoV-2 Total. Methods: Specimens from 175 PCR-positive patients and 107 control specimens were analyzed using Abbott IgM and IgG, DiaSorin IgG, and Roche Total (IgA, IgG, IgM) assays. Sensitivity, specificity, cross-reactivity, concordance between assays, trends over time, positive predictive value (PPV), and negative predictive value (NPV) were determined. Results: Abbott IgM sensitivity was 63.6% at 0 days post-PCR positivity, 76.5% at 1-5d, 76.3% at 6-14d, 85.2% at 15-30d, and 63.6% at >30d. All assays exhibited highest sensitivity 15-30d post-PCR positivity (83.3-85.2%). Combining Abbott IgM and IgG improved sensitivity by 22.7% compared to IgG alone when tested 0d post-PCR positivity. All assays had a specificity of 100% and only Abbott IgG exhibited cross-reactivity (anti-dsDNA). Cohen's kappa varied between 0.86-0.93. Time to seroconversion from PCR positivity was lowest for Abbott IgM and highest for Abbott IgG. NPV was highest for Abbott IgM <14 days post-PCR positivity and Abbott IgG ≥14 days. Conclusion: The Abbott IgM assay exhibited the earliest response and greatest signal in most patients evaluated for serial sampling and had the highest NPV <14 days post-PCR positivity, suggesting its potential utility as an adjunct test to PCR early in disease course.

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