The causes and diagnosis of influenza-like illness.

Influenza and other respiratory viruses circulate between spring and autumn in temperate climates and all year in tropical climates. These viruses cause symptoms often referred to as influenza-like illness (ILI), but are not generally distinguishable on clinical grounds alone. This article provides a brief review of the surveillance, viral causes and current diagnostic methods used to identify viruses causing ILI. Influenza-like illness surveillance with laboratory support, conducted in most Australian stats and territories, aims to define the impact of influenza seasons in the community and provide virus strains that may be used in future vaccine formulations. Surveillance may also be useful in the early stages of an influenza pandemic. In addition to influenza, viruses known to cause ILI include respiratory syncytial virus, rhinovirus, adenovirus, parainfluenza viruses, human coronaviruses (including the virus that causes severe acute respiratory syndrome) and the recently recognised human metapneumovirus. Polymerase chain reaction assays are the most common diagnostic tests now used for the differential diagnosis of ILI.