She was 5 years old, medically fragile and born with a poor immune system. So she was, in her mother's words, a prime candidate to succumb to the dangers of the swine flu.

Last week, the Minneapolis girl -- who has not been publicly identified -- died a day after she was hospitalized, the first death in Minnesota associated with swine flu.

Officially, the number of confirmed cases in Minnesota stood at 274 Monday, but health officials readily acknowledge that the true number is far greater, and that it's largely affecting children and young adults.

An average of 300 children a day are now flooding the emergency rooms at Children's Hospitals and Clinics of Minnesota -- about 50 percent more than normal, officials say. "It's mostly kids with influenza-like symptoms; fever, cough, sore throat," said Patsy Stinchfield, the hospital's director of infection control. "What we're seeing is a lot of sick children."

The girl who died was taken to Children's Hospital of Minneapolis suffering from respiratory distress last Wednesday, the girl's mother said.

"The minute we walked in, [health care providers at Children's] were under the impression that it was influenza," the mother said. The girl died a day later, on June 11, the same day the World Health Organization declared swine flu a global pandemic. Lab tests later confirmed that the girl had the new strain of flu.

Her mother described the girl, a preschooler with special needs, as a "joyful, amazing gift that we are grateful to have in our life." She said she wants the public to know that her daughter's lifelong medical problems put her at especially high risk for flu complications. "I just don't want people to panic," she said.

The Health Department announced Monday that the child had died, although it did not say what role the flu, also known as H1N1, played in her death.

"Our sympathies go to the family and loved ones of the child," said state epidemiologist Dr. Ruth Lynfield. "For most people, the H1N1 flu is causing mild illness, however, it can still be very serious, especially for people with underlying health conditions. That's why we continue to monitor the situation very closely."

At this point, no one knows how many people in Minnesota have been infected with swine flu. After the first few weeks, the Health Department stopped trying to test every potential case and started tracking cases only at hospitals and a select number of clinics.

"We would expect that there's a significant number of cases for every case that we've been tracking," said John Linc Stine, assistant health commissioner. He said it would be difficult, and unnecessary, to track every case at this point. "It's clear to us that the virus is spreading through the state, through the population."

The state uses its monitoring program mainly to watch for signs that the flu is changing or causing more severe illness.

While some clinics have reported little evidence of the flu, Children's Hospitals and Clinics is feeling the brunt of the outbreak, officials say. "We're seeing about a third of the [confirmed] Minnesota cases," said Stinchfield, a nurse practitioner and infectious disease expert. "We don't want to get too obsessed with the numbers," she said, noting that "they're probably just a fraction of what's happening in the state of Minnesota." But she said they show that the epidemic isn't slowing down yet.

So far, Children's has treated 86 confirmed cases, including 25 children who have been hospitalized, several of them in intensive care, she said. The two emergency rooms, in Minneapolis and St. Paul, are busier now than in the typical winter flu season, she said.

That doesn't even count patients like her daughter Shannon, 17, who spent last week home in bed with all the classic symptoms, from fever to muscle aches and sore throat. "She was quite, quite miserable," Stinchfield said. "She's just an example of many mild cases that are out there that aren't in these numbers." Technically, "she was a probable case."

Yet the ripple effect has been far less noticeable at the Mayo Clinic in Rochester, said Dr. William Marshall, an infectious disease specialist. "We're not seeing anything out of the range for what we usually see for respiratory illnesses," he said.

But that could change. As of last week, more than 17,000 cases have been confirmed nationwide, including 45 deaths.

"This flu is very widespread, and we expect to see many more cases across the state," said Lynfield, the state epidemiologist. She urged people to continue taking the simple precautions that can prevent the spread of flu: washing hands frequently with soap and water or an alcohol-based solution, coughing into the crook of your elbow, avoiding sick people and staying home for seven days if you are sick.

Star Tribune staff writer Tim Harlow contributed to this report. Maura Lerner • 612-673-7384 Paul Walsh • 612-673-4482