Children and younger adults will be the most affected in the approaching flu season, especially the H1N1 or "swine" flu, according to experts.

That's led some in the medical field to reconsider their approach to allowing contact between patients and visiting family members who could spread the disease in hospitals.

State health officials estimated that millions of Californians could contract the H1N1 flu virus in the coming months, and with H1N1's track record thus far of affecting the young, that could mean day-care centers, schools and colleges could become the Petrie dishes for any emerging strain, doctors said.

"The fall flu season is quickly approaching, and this year we know it will be different," Mark B. Horton, director of the California Department of Public Health, wrote in a public letter on Aug. 25.

"While none of us can predict the course of the novel H1N1 influenza outbreak, it has the potential to sicken millions of people in our state in the months ahead; as many as 1 in 4 Californians may be affected," he wrote.

At Lucile Packard Children's Hospital, officials are keeping a close watch over the virus. Confirmed cases thus far have been mild, but one of the greatest risks is that people don't have immunity to this strain, according to Dr. Yvonne Maldonado, chief of pediatric infectious diseases at Lucile Packard Children's Hospital.

The U.S. Centers for Disease Control released its H1N1 guidelines on Tuesday, which included treating high-risk patients suspected of having the disease before the results of lab tests come in, she said.

Although no one has died at Packard from the illness and there are no cases of transmission of the disease within the hospital, officials might take a stringent approach to curb spread of the disease, Maldonado said.

"As time goes on, we may have to be stricter about who comes into the hospital. Packard prides itself on "family-centered care. But we may have to limit (visitors) who are sick if it becomes more widespread," she said.

In particular, hospital officials will be looking at the school-age population and may prevent siblings from visiting brothers or sisters receiving treatment at Packard, she said.

The current H1N1 strain varies from the usual garden-variety flu strains.

"Fever tends not to be as high, but it's more likely that children will have even more gastrointestinal disease," she said.

The one good bit of news: "There is evidence that it doesn't transmit that well," she said.

A recent up-tick in visits to the doctor at hospitals and clinics could reflect greater caution as opposed to greater illness, she added.

"I'm hearing from the medical community that they are seeing a lot of patients coming in," she said, but that factor could be caused by some schools requiring doctor's notes to clear sick students of having the H1N1 disease, she said.

So far, there doesn't appear to be a spike in confirmed flu cases. Palo Alto Medical Foundation spokeswoman Jill Antonides said despite rumors, she hasn't heard of any increase in the number of cases. Judy Twitchell, communications manager at El Camino Hospital in Mountain View, agreed.

Santa Clara County Public Health Department has stopped tracking the number of cases and is now focusing on the number of hospital cases and deaths.

"What we want to know is if it is changing and getting stronger," spokeswoman Joy Alexiou said.

Maldonado said the fall scenario for a potential pandemic is based on what happened during the 1918 flu pandemic.

If the milder strain does mutate this fall, state officials said it will take a concerted effort for everyone to work together. Californians should plan to care for their ill children at home for several days; individuals must also prepare for potential school closures; businesses must prepare for the possibility that large numbers of employees could be sick at the same time.

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