Flu Activity Across the United States

ILI stands for influenza-like illness — fever (100°F or higher) plus cough or sore throat. The CDC's ILINet network of healthcare providers across all 50 states reports the percentage of patient visits for these symptoms each week.

Different surveillance systems measure different things. ILINet tracks doctor visits, NSSP tracks emergency department visits, and wastewater surveillance measures viral concentrations in sewage. Each gives a different view of flu activity. Learn more about why sources disagree .

Flu data is updated weekly, typically on Fridays, after the CDC publishes new FluView surveillance data. There is usually a 1-2 week lag between when illness occurs and when data appears here.

Rt (the time-varying reproduction number) measures how many people each infected person spreads the virus to, on average, at a given point in time. When Rt is above 1.0, the epidemic is growing — each case generates more than one new case. When Rt is below 1.0, the epidemic is declining. The CDC's Center for Forecasting and Outbreak Analytics estimates Rt weekly for each state. We display these estimates on individual state pages.

Based on the latest CDC Rt estimates, flu is declining in 35 states, stable in 11 states, and growing in 1 states. The national median Rt is 0.90, which means flu activity is generally declining across the country. Check your state's page for specific forecasts.