This is a catch-all term that refers to influenza and other respiratory illnesses in the CDC’s surveillance systems for respiratory disease. It’s defined as a fever (at least 100ºF or 37.8ºC) with a cough and/or sore throat. Up until 2021-2022, the definition included “without a known cause other than influenza,” but that part of the definition has been removed by the CDC. Other symptoms that can accompany ILI include chills, shivering, headache, general malaise, loss of appetite, body aches, nausea and sneezing. ILI surveillance is tracked on the CDC’s interactive FluView system and reported in weekly FluView reports. Common causes of ILI include influenza, COVID-19, RSV, the common cold, rhinoviruses, adenoviruses, human parainfluenza viruses, SARS, pneumonia, and other viral and bacterial infections.
