The nation's flu positivity test rate reached nearly 10 percent in mid-April, making it the first time such an increase has occurred so late in the flu season since 1982, according to an NBC News analysis of CDC flu data from the past seven years.
"We aren't used to thinking of flu in May, but it's definitely still out there," Lynette Brammer, head of the CDC's domestic influenza surveillance team, told NBC May 9.
Flu season typically starts in October and peaks between December and February. The current season has still seen far fewer cases than past years. For example, the current season's positivity rate hasn't exceeded 10 percent, while previous seasons have seen peaks of more than 30 percent. Still, the unusually late uptick has brought positivity rates closer to what they would be at the end of a typical flu season.
The CDC estimates there have been at least 5.7 million flu cases, 59,000 hospitalizations and 3,600 flu-related deaths so far this season. The agency's latest FluView report for the week ending April 30 shows flu hospitalizations fell for the first time since January.