Flu Cases Are on the Rise in the U.S. Here's What You Need to Know With colder weather and more indoor gatherings on the horizon, flu season has taken hold, and data from the Centers for Disease Control and Prevention (CDC) show that there are high levels of influenza-like illnesses in four states, in particular -- Louisiana, New York, Colorado, and New Jersey, reports ABC News. The CDC data also shows 8.1 percent of weekly tests were positive for flu, four times higher than one month ago.