Correlations of GOPC, GP ILI rate, school absenteeism, DFC fever counts and inferred influenza level from the dynamic linear model with the influenza activity^* in pre-pandemic, pandemic and the whole period, January 2004–December 2009.

DFC designated fever clinic; GOPC general outpatient clinic; GP general practitioner; ILI influenza-like-illness. *Influenza activity measured by GP ILI consultation rate×laboratory influenza isolation rate. †Correlations between surveillance data and laboratory isolation rate were calculated by fitting a univariate dynamic linear model to each data stream, and an overall multivariate model to all data streams. ‡GOPC data were interrupted during the pandemic period due to the opening of designated flu clinics. §School absenteeism data were occasionally interrupted by school holidays or school closures. Correlations were calculated excluding data during the summer holidays. ¶8 designated fever clinics were activated in place of GOPCs to treat outpatients with influenza-like illness from mid-June 2009 to May 2010.