A Proof Of Concept For A Syndromic Surveillance System Based On Routine Ambulance Records In The South-west Of England, For The Influenza Season 2016/17

Thilo Reich; Marcin Budka

As the daily patient count varies considerably from one day to another resulting in a noisy time series, the data was smoothed using an Exponential Moving Average (EMA) with an averaging window of 21 days. This window size was chosen because the incubation period of influenza can be up to 3.6 days [18] followed by an onset of symptoms and transmission period of the virus, which can last up to 10 days in hospital [19] [20] [21] . This means a patient could be contagious for up to 14 days following infection. Accounting for the incubation period, a secondary patient could show symptoms ∼ 18 days after the infection of the index case. Therefore, the averaging window size was chosen to be 21 days as this allows for some leeway.