The United States is in the midst of late-season rise in flu, data from the Centers for Disease Control and Prevention shows, with nearly 1 in 10 positive tests reported at the mid-April peak.
But even with that uptick, an NBC News analysis of 7 years CDC data shows that this year’s flu season is still far below pre-pandemic levels.
"We're on the late side of things," said Dr. Carrie Horn, the chief medical officer at National Jewish Health in Denver. "But they're not so high that we're saying that there's a flu epidemic."
It will be the first time since 1982 that such an increase has occurred so late in the typical flu season, said Lynnette Brammer, the head of the CDC's domestic influenza surveillance team.
"We aren't used to thinking of flu in May, but it's definitely still out there," Brammer said, adding that it's possible rates could rise more this season.
While this season has had far fewer cases than past seasons, the late-season uptick has brought positivity rates closer to where they would be at the end of a typical flu season.
So far this season, the CDC reported, there have been at least 5.7 million cases of flu and an estimated 59,000 hospitalizations. About 3,600 people have died, including 24 children.
Respiratory illnesses are spiking in New Mexico and Colorado in particular, according to the latest CDC flu data.
Doctors there say patients are coming in with fever, cough, body aches — which could signal the flu, Covid-19 or a number of other respiratory viruses.
"Almost daily, I see at least one person with a case of something that we have to sort out," said Dr. Melissa Martinez, a professor of internal medicine at University of New Mexico Health Sciences.
But it's indeed the flu that's proving to be behind a number of the current respiratory illnesses, Martinez said. Within the past few weeks, the proportion of positive Covid tests within the UNM Health Sciences system has hovered around 4 percent, she said, while the proportion of positive flu tests are up to 17 percent.
The timing of flu cases is unusual, Martinez said. "To see an uptick in influenza this late in the season is really odd."
Flu generally spreads through respiratory droplets when a person sneezes, coughs or even talks. The uptick has coincided as Covid-19 masking has largely fallen to a minimum nationwide.
Despite the increases in flu cases, Martinez said, the overall number of influenza cases is low compared to previous seasons.
"It's a drop in the bucket compared to what we've seen in other years," she said.
While the current season's test positivity rate hasn't exceeded 10 percent yet, previous seasons in the recent past peaked at upwards of 30 percent.
The dominant strain this year has been H3N2, which experts say tends to be more virulent and often causes more severe illness.
Because cases are peaking so late in the season, there is still time to get a flu shot, Brammer said, even though the vaccine is a less than ideal match for the current strain that's circulating.
Testing to determine the cause of a respiratory illness — whether it's the flu or Covid — is critical, Martinez said. Antiviral treatments specific to both viruses are available, but they work best when they are given early on in the course of disease.
"We really want to start them on the correct treatment as soon as possible," she said.