Long-term follow-up of HIV-2-related AIDS and mortality in Guinea-Bissau: a prospective open cohort study by Esbjörnsson, J, Månsson, F, Kvist, A, Da Silva, Z, Andersson, S, Fenyö, E, Isberg, P, Biague, A, Lindman, J, Palm, A, Rowland-Jones, S, Jansson, M, Medstrand, P, Norrgren, H, Sweden And Guinea-Bissau Cohort Research Group