Funding for this research was provided by:
National Institute for Health Research (Health Protection Research Unit in Gastrointestinal Infections)
Received: 20 June 2019
Accepted: 23 December 2019
First Online: 31 December 2019
Ethics approval and consent to participate
: Ethical approval was not required as these data were collected for public health surveillance under The Health Protection Legislation (England) Guidance 2010. No administrative permissions were required to access the raw data used in this study.
: Not applicable.
: The authors declare that they have no competing interests.