This image taken through a microscope shows the H1N1 strain of the swine flu virus.

PORTLAND, Ore. - State health officials said Tuesday they were scaling back their response to the H1N1 "Swine" flu after evidence suggested it was behaving like a typical seasonal flu.

"I am relieved," said Dr. Mel Kohn, Oregon's public health director, during an afternoon press conference Tuesday. "I don't feel like we are totally out of the woods yet."

Officials are also no longer recommending that schools close in response to a swine flu case, he said. Instead, ill students should just stay home until they are well.The U.S. Centers for Disease Control and Prevention gave the same guidance to the nation earlier in the day.

Late Tuesday afternoon, officials with the Forest Grove School District sent word that all of their schools would reopen Wednesday, including Cornelius Elementary.

Meanwhile, the number of confirmed cases of swine flu in Oregon rose to 21, including:

7 in Multnomah County
5 in Lane County
5 in Polk County
2 in Washington County
2 in Umatilla County

Of those, six are children, five are teenagers and 10 are adults.

There are 50 additional specimens still to be tested for the troublesome strain of flu, Kohn said. Only one person has been hospitalized so far.

The state plans to update the tally of confirmed H1N1 flu cases on its Web site - http://www.flu.oregon.gov/ - and is not expected to continue daily media briefings.

Kohn said there is concern for how the virus may resurface in the fall. In the world's most devastating global flu epidemic in 1918, the first wave of cases in the spring were mild. Then, the virus evolved and came back in the fall as a strain that proved truly deadly, flu experts say. So scientists today are watching to see if that could happen again.

"None of us have immunity so we are more likely to be more susceptible to it," Kohn said. "... I feel the weight of all the work we have to do to prepare for the fall. The fall will be here before we know it."

- The Associated Press contributed to this report