Evaluating the population impact of hepatitis C direct acting antiviral treatment as prevention for people who inject drugs (EPIToPe) – a natural experiment (protocol) by Jeremy Horwood, Andrew Radley, John F Dillon, Peter Vickerman, Rory N Gunson, Mary Ramsay, Chris Metcalfe, William Hollingworth, Hannah Fraser, Helen Harris, Ellen Heinsbroek, Lawrie Elliott, Paul Flowers, Sema Mandal, Matthew Hickman, David Goldberg, Natasha Martin, Emma Hamilton, Daniela De Angelis, Graham Foster, Peter Donnan, Ann Eriksen, Samreen Ijaz, David Liddell, Lewis J Z Beer, Kate Drysdale, Rachel Glass, Lesley Graham, Ross Harris, Vivian Hope, Sarah Karen Inglis, Hamish Innes, Athene Lane, Jade Meadows, Andrew McAuley, Stephanie Migchelsen, Alex Murray, Gareth Myring, Norah E Palmateer, Anne Presanis, Pantelis Samartsidis, Ruth Simmons, Katy Sinka, Gabriele Vojt, Zoe Ward, David Whiteley, Alan Yeung, Sharon J Hutchinson