©  The  Author(s)  2019.  Published  by  Oxford  University  Press  for  the  Infectious  Diseases  Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium,  provided  the  original  work  is  not  altered  or  transformed  in  any  way,  and  that  the  work  is  properly  cited.  For  commercial  re-use,  please  contact  journals.permissions@oup.com
Except where otherwise noted, this item's license is described as © The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com