Arizona's flu and RSV activity is peaking earlier than usual, according to the state Department of Health Services.
The latest report shows there were 851 cases of lab-confirmed influenza for the week that ended Feb. 12, just slightly less than the previous week.
Activity of the virus usually picks up in the early part of each year, but this is earlier than usual, said Shoana Anderson, office chief for the state's office of infectious disease services.
"We're definitely on the upswing for flu activity. It is a little unusual. It's hard to say why that happens," she said.
There may be many more people experiencing the flu, since most people don't get tested for it.
Influenza is a respiratory virus that thrives in colder weather, though it can be seen year round.
About 50 percent of the confirmed cases this year have been in children younger than 18, Anderson said. There have been three pediatric deaths connected to influenza in the state this year, including two in Maricopa County.
As of Friday, Mesa's Cardon Children's Medical Center reported that 63 of its 110 inpatients have tested positive for the flu, RSV (respiratory syncytial virus) or pneumonia, all respiratory illnesses. Compared to the prior week, the hospital saw double the number of positive influenza cases.
Anderson said the state could continue to see high numbers of the illnesses for the next few weeks. The number of influenza cases is about normal for the state. Last year, figures overall were much higher because of the pandemic.