Funding for this research was provided by:
National Institute for Health Research (HPRU-2012-10047)
Received: 27 February 2019
Accepted: 5 June 2019
First Online: 13 June 2019
Ethics approval and consent to participate
: The collection and use of samples and consent process was approved by the Camden and Islington National Research Ethics Committee (Reference 14/LO/2217).
: Not applicable.
: The authors declare they have no competing interests.