Arizona health officials say flu activity is widespread in the state this week with influenza reported in 14 of its 15 counties.

State Department of Health Services officials say about 1,000 of the nearly 2,200 flu cases were reported last week. Because many people aren’t tested for the flu, officials say that number likely is just a fraction of the true number of cases.

There’s also been an increase in hospital admissions for flu cases, especially in central Arizona.

Influenza is a serious viral illness with symptoms similar to the common cold, but it comes on quickly and is more physically draining.

Arizona typically sees most of its flu cases in February or March. Officials say influenza can be unpredictable and can peak either earlier or later in the season.