Detecting the start of an influenza outbreak using exponentially weighted moving average charts

BACKGROUND: Influenza viruses cause seasonal outbreaks in temperate climates, usually during winter and early spring, and are endemic in tropical climates. The severity and length of influenza outbreaks vary from year to year. Quick and reliable detection of the start of an outbreak is needed to promote public health measures. METHODS: We propose the use of an exponentially weighted moving average (EWMA) control chart of laboratory confirmed influenza counts to detect the start and end of influenza outbreaks. RESULTS: The chart is shown to provide timely signals in an example application with seven years of data from Victoria, Australia. CONCLUSIONS: The EWMA control chart could be applied in other applications to quickly detect influenza outbreaks.