Attribution-NonCommercial-NoDerivs 3.0 United States
This is an open access article originally published at https://doi.org/10.1186/s12879-017-2517-3
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 3.0 United States This is an open access article originally published at https://doi.org/10.1186/s12879-017-2517-3