HCV Genotype 1 or 4 with HIV co-infection study

This is an "open-label" study, which means that both the participant and the doctor will know what study drug is being taken. This study will enroll approximately 300 participants at about 60 study sites in North America and New Zealand. Participation will be approximately 40 weeks, and is broken down into 3 parts: Screening, Study Treatment and Follow-up. The screening period can last up to 28 days. During this time, the study doctor will do some tests or procedures to make sure the patient meets the requirements to enroll on the study. The study treatment will last for 12 weeks, and includes 8 visits lasting 1 to 2 hours each. Participants will take the sofosbuvir/ledipasvir fixed dose combination tablet (SOF/LDV FDC) for 12 weeks. The fixed dose combination tablet consists of 400mg sofosbuvir and 90 mg of ledipasvir, and will be supplied by Gilead Sciences, Inc. (the sponsor). The SOF/LDV FDC should be taken by mouth once daily with or without food. The SOF/LDV FDC tablet should never be crushed or split. The SOF/LDV FDC tablet should be stored at room temperature. After the 12 weeks of taking the study drug, there will be up to 24 weeks of follow-up, including up to 3 visits lasting 1 to 2 hours each. There is an optional retreatment sub-study. Once the follow-up period for the main study is complete, if the Hepatitis C has still not been cleared from their body, the participant may choose to enroll on the optional retreatment study. The retreatment study is also “open label,” and includes the sofosbuvir/ledipasvir fixed dose combination table and ribavirin. The SOF/LDV FDC tablet and ribavirin will be taken for 24 weeks (includes 8 visits lasting 1 to 2 hours each), followed by 24 weeks of follow-up, which includes 3 visits lasting 1 to 2hours each. There is also an optional pharmacogenetic sub-study. Participants can take part in the main study and still say no to the optional pharmacogenetic sub-study.