[1] Univ Bristol, Bristol Med Sch, Populat Hlth Sci, Bristol, Avon, England
[2] London Sch Hyg & Trop Med, Fac Publ Hlth & Policy, London, England
[3] Publ Hlth England, London, England
[4] UNSW, Kirby Inst Infect & Immun, Sydney, NSW, Australia
[5] Glasgow Caledonian Univ, Hlth & Life Sci, Glasgow, Lanark, Scotland
[6] Publ Hlth Wales, Subst Misuse Drugs & Alcohol, Cardiff, S Glam, Wales
[7] Univ West Scotland, Sch Media Soc & Culture, Paisley, Renfrew, Scotland
[8] Univ Calif San Diego, Dept Med, San Diego, CA 92103 USA
[9] Bristol Drugs Project, Bristol, Avon, England
[10] Univ Dundee, Sch Med, Dundee, Scotland
[11] Liverpool John Moores Univ, Publ Hlth Inst, Liverpool, Merseyside, England
[12] Hlth Protect Scotland, Blood Borne Viruses & Sexually Transmitted Infect, Glasgow, Lanark, Scotland