Balancing uncertainty and proactivity in care seeking for hepatitis C: qualitative research with participants enrolled in a treatment trial in Ho Chi Minh City, Vietnam by Nguyen Le Thao, M, Nguyen Thi Hong, Y, Dang Trong, T, Dung, NT, Day, J, Phuong, LT, Kestyln, E, Chau, NVV, Le Manh, H, Van Nuil, JI