Statistics and Epidemiology, Warwick Medical School, University of Warwick, Coventry, UK.|Real-time Syndromic Surveillance Team, National Infection Service, Public Health England, Birmingham, UK.|School of Environmental Sciences, University of East Anglia, Norwich, UK.|Real-time Syndromic Surveillance Team, National Infection Service, Public Health England, Birmingham, UK.|Real-time Syndromic Surveillance Team, National Infection Service, Public Health England, Birmingham, UK.|School of Environmental Sciences, University of East Anglia, Norwich, UK.|Population Evidence and Technologies, Warwick Medical School, University of Warwick, Coventry, UK.