Every year influenza (‘flu’) puts a major strain on UK hospitals. Whilst many patients are admitted with influenza, other patients can get it during their hospital stay. This is because it is very easy to transmit, and it is not always obvious who has flu. We are using genetic sequencing to work out the ‘letters’ of the influenza virus’s genetic code. We would now like to understand whether patients with more similar viruses have spent more time together on wards in our hospital, and which wards these are. We want to work out whether there are ways that we could reduce the chance of patients getting flu in our hospitals.