- Correspondence to Dr Carri Westgarth, Department of Epidemiology and Population Health, Institute of Infection and Global Health, Faculty of Health and Life Sciences, University of Liverpool, Leahurst Campus, Chester High Road, Neston, Cheshire CH64 7TE, UK;
- Received 5 August 2015
- Revised 9 December 2015
- Accepted 11 December 2015
- Published in print 1 December 2016.
- Published online 22 November 2016.
- Published first 12 January 2016.
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- Data supplement 1 - Online supplement
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