Identifying and testing a threshold for action for co-circulating community influenza-like illness on a 5-week military training exercise

During all military activities, there is a background level of sub-clinical influenza-like illness (ILI), which may be symptomatic but does not require clinical or public health action.1 Identifying when the rate of ILI exceeds expected levels can give early warning indications of an emerging outbreak.2 In high-density institutions, such as military settings, there is an increased risk of rapid transmission of respiratory illness leading to large outbreaks and therefore increased morbidity and mortality.3 Early identification of exceedances allows rapid implementation of control measures to limit transmission, minimise morbidity or isolation and thereby maintain operational effectiveness.