Time to act: a call for comprehensive responses to HIV in people who use drugs. - Beyrer C; Malinowska-Sempruch K; Kamarulzaman A; Kazatchkine M; Sidibe M; Strathdee SA; Beyrer, Chris; Malinowska-Sempruch, Kasia; Kamarulzaman, Adeeba; Kazatchkine, Michel; Sidibe, Michel; Strathdee, Steffanie A (Lancet, 2010)