The Arizona Department of Health Services said there have been more than 19,000 reported cases of influenza this season so far.

That is the highest number reported since the 2009-2010 flu season, which was the time of the H1N1 epidemic.

According to the state health department, last year by this time there were only 2,175 cases reported. 

Jessica Rigler is with the state health department. She said that flu seasons are always unpredictable.

"If you compare this year to our five-year averages, we're seeing 400 percent more cases at this time then we would typically see," Rigler said.

Rigler said most cases have been reported in adults over the age of 50.

Among people at high risk of serious complications of flu include children under 5 years old, adults 65 years or older, and people with chronic disease.

The department urges people to get vaccinated if they haven't already, and to stay home from work or school if feeling sick.