ILI surveillance source: Analysis of the relationships between the signals for PAN, ED and CC are heavily influenced by a strong day of the week effect in the PAN data. Considering all of the data, including periods of high and low ILI activity, the correlation between ED and PAN shows a stronger relationship when the ED signal lags the PAN by 1 day (r 00.653 vs. r 0 0.617). There is a less clear relationship between ED and CC with the strongest correlation occurring when CC lags ED by 2 days (r 00.669 vs. r 00.659). The relationship between CC and PAN is unclear. These relationships are also all valid when just considering the period of the 2009 H1N1 pandemic, but interestingly not the last strong seasonal influenza in 2008. For the 2008 season, for which we do not have ED data, the signal for CC clearly lags the signal for PAN with a peak correlation at a lag of 6 days (r00.561 vs. r00.413). ILI and climate: There are significant negative correlations between all three signals and daily temperature, e.g., CC and Tmin (r0(0.265, df 02004, p B 0.0001), but not precipitation, e.g., CC (r 0(0.011) when considering all data. There are no clear relationships between temperature or precipitation and CC or PAN during the 2008 seasonal outbreak, but there is a clear negative correlation between temperature and CC, PAN and ED during the 2009 H1N1 pandemic, e.g., ED and Tmin (r0(0.366, df 0 119, pB 0.001). There was no clear correlation with precipitation.