Mixed-methods protocol for the WiSSPr study: Women in Sex work, Stigma and psychosocial barriers to Pre-exposure prophylaxis in Zambia oleh Anjali Sharma, Michael E Herce, Maurice Musheke, Chama Mulubwa, Ramya Kumar, Deepa Rao, Jamia Phiri, Martin Zimba, Maureen Phiri, Ruth Zyambo, Gwen Mulenga Kalo, Louise Chilembo, Phidelina Milambo Kunda, Benard Ngosa, Kenneth K Mugwanya, Wendy E Barrington