<qa>  What is the main limitation of the study?The investigator is aiming to recruit 45 participants in to each group. The participants will be asked to attend for 2 visits in total one year apart. One major limitation of this study is the frequency of sampling for HCV RNA. By doing this annually the investigators may miss those reinfections that the patient clears spontaneously. However, the investigator feels that it is those with persistent viraemia and therefore persistent reinfection that are important to quantify. This is because much of the physicians reluctance to treat active drug users comes from the perception that reinfection will occur resulting in the need for further repeated courses of treatment. Whilst those transient reinfections that the investigators may miss are very important in terms of onwards transmission, they largely do not result in the need for further treatment. 