These are self-help groups based along spiritual (but not religious) principles. The only requirement for attending meetings is a desire to recover from the relevant addiction. They are named Anonymous because members identify themselves at meetings by first name only: confidentiality is held to be very important.
The focus is on recovery from addiction - be it drugs, alcohol, destructive relationships, food, gambling or sex. However, people can and do talk about any aspect of their lives and recoveries, and that can certainly include illness.
You will find that some of the Fellowships, in particular NA (Narcotics Anonymous), have many members with hepatitis C. Although it is not their primary purpose, meetings can be a good source of information and support if you also happen to be (or aim to be) a recovering addict. If so, NA and AA both have special topic ‘Illness in Recovery’ meetings, where there is a focus on living with and dealing with illness in recovery.
For details of how to contact the 12 step fellowships: NA (Narcotics Anonymous), Cocaine Anonymous and AA (Alcoholics Anonymous) see Drug and Alcohol Support