Can syndromic thresholds provide early warning of national influenza outbreaks?
Regional Surveillance Unit, West Midlands Health Protection Agency, 9th Floor, Ladywood House, 45 Stephenson Street, Birmingham B2 4DY, UK. duncan.cooper@hpa.org.uk BACKGROUND: Influenza incidence thresholds are used to help predict the likely impact of influenza and inform health professionals and the public of current activity. We evaluate the potential of syndromic data (calls to a UK health helpline NHS Direct) to provide early warning of national influenza outbreaks. METHODS: Time series of NHS Direct calls concerning ‘cold/flu’ and fever syndromes for England and Wales were compared against influenza-like-illness clinical incidence data and laboratory reports of influenza. Poisson regression models were used to derive NHS Direct thresholds. The early warning potential of thresholds was evaluated retrospectively for 2002-06 and prospectively for winter 2006-07. RESULTS: NHS Direct ‘cold/flu’ and fever calls generally rose and peaked at the same time as clinical and laboratory infl
