U.S. Outpatient Respiratory Illness Surveillance
The U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) monitors outpatient visits for respiratory illness referred to as influenza-like illness [ILI (fever plus cough or sore throat)], not laboratory-confirmed influenza, and will therefore capture respiratory illness visits due to infection with pathogens that can present with similar symptoms, including influenza viruses, SARS-CoV-2, and RSV.
It is important to evaluate syndromic surveillance data, including that from ILINet, in the context of other sources of surveillance data to obtain a more complete and accurate picture of influenza, SARS-CoV-2, and other respiratory virus activity.
CDC is providing integrated information about COVID-19, influenza and RSV activity on a website that is updated weekly. Information about other respiratory virus activity can be found on CDC’s National Respiratory and Enteric Virus Surveillance System (NREVSS) website.
U.S. Weekly Influenza-like Illness Update
Last Updated: March 8, 2024
Nationwide, during Week 9, 4.1% of patient visits reported through ILINet were due to respiratory illness that included fever plus a cough or sore throat, also referred to as ILI. This has decreased (change of > 0.1 percentage points) compared to Week 8. The percentage of visits for ILI remained stable in regions 2, 3, 5, and 7, and decreased in regions 1, 4, 6, 8, 9, and 10 in Week 9 compared to Week 8. Regions 8 and 10 are below their region-specific baselines in Week 9 for the first time since early and mid-November respectively, while all other regions remain above their region-specific baselines. Multiple respiratory viruses are co-circulating, and the relative contribution of influenza virus infection to ILI varies by location.
Weekly U.S. ILINet Map