where Cusum t d ≤ + + = 7 0 . X t  and st  are the 7-week moving average and standard deviation of ILI cases in weeks t-d-1 to t-d-7 Note that d stands for a delay period and this method will only be informative from the (d+8) th week onwards. An alarm is triggered using this method when Cusum t + on a week t crosses a pre-set threshold [21] . Using the SERVIS ILI data for six seasons we preset the threshold values for this method for all 16 (Table  in Additional file 3) . Therefore, this combination is used to make comparisons with other methods.