This non-interventional clinical study will be conducted to prospectively collect serial plasma and serum samples from treatment naïve subjects with chronic HCV infection who are initiating sofosbuvir-based therapy. These samples will be used to estimate clinical utility endpoints for the Aptima HCV Quant Dx assay which is used an aid in the management of HCV-infected patients undergoing HCV antiviral therapy.

Inclusion Criteria:

• The subject is chronically infected with HCV genotypes 1, 2, 3, 4, 5, and/or 6 as documented in the subject's medical records and is naïve to HCV treatment (treatment naïve).

• Chronic HCV (with or without HIV [human immunodeficiency virus] co-infection) will be documented with historical record of:

• A positive HCV RNA test result (result generated at least 6 months before the baseline visit)

• A HCV genotype test result (result generated at least 6 months before the baseline visit)

• A liver biopsy report demonstrating chronic HCV

  ---The subject is initiating antiviral therapy with a sofosbuvir regimen as indicated below:

• Sofosbuvir plus peginterferon and ribavirin for 12 weeks (peginterferon eligible genotype 1, 4, 5, or 6)

• Sofosbuvir plus ribavirin for 12 weeks (genotype 2)

• Sofosbuvir plus ribavirin for 24 weeks (peginterferon ineligible or unwilling genotype 1 or genotype 3)

• The subject is at least 18 years of age at the time of enrollment

• Adequate medical records are available for collection of protocol-defined demographics, baseline patient characteristics, medical history, virology and specific laboratory results, and other information to verify enrollment criteria

• The subject and/or legally authorized representative is willing and able to provide consent prior to providing a specimen(s)

Exclusion Criteria:

• Subjects with history or evidence of decompensated liver disease
• Subjects with severe renal impairment or end stage renal disease
• Subjects who are not naïve to HCV therapy with prior exposure to an approved or experimental HCV antiviral therapy
• Subject has characteristics that are contraindicated in the FDA approved label for sofosbuvir (eg, subjects with contraindications applicable to peginterferon and/or ribavirin, pregnant woman or men whose female partners are pregnant; Sovaldi Package Insert 2013)
• Subject is receiving treatment pre- or post-transplant
• Subject is unsuitable for study participation based on the Investigator's decision (eg, unlikely to comply with study visit schedule, significant medical complication)
• Participating in another investigational study that the Investigator believes might interfere with the subject's participation in this study

Treatment naïve men and women ≥18 years of age with chronic HCV infection initiating sofosbuvir-based treatment will be enrolled from medical facilities that may include private and academic family practice, infectious disease, hepatology, gastroenterology, and medical group clinics.