The number of confirmed swine flu cases has risen to 11 in California, indicating the possibility of a pandemic in the state, health officials said on Tuesday.

Five cases were documented in San Diego County, five in adjacent Imperial County and one in Sacramento. At least another six people in San Diego County are suspected of having contracted the disease, the California Department of Public Health (CDPH) said.

The other 39 confirmed cases in the United States are in New York, Texas, Ohio and Kansas, and most are mild, but one person was hospitalized with complications, according to published reports.

No US fatalities have been reported as of Tuesday morning.

Meanwhile, Los Angeles health officials said they were certain swine flu is already present in the area, even though no cases had been confirmed as of Monday.

"It's here. Just a matter of time," said Laurene Mascola, director of the Los Angeles County Department of Public Health's Acute Communicable Disease Control.

The disease appears much like regular influenza, so it likely just hasn't been spotted yet, Mascola said, adding that it can take between two to four days to test a culture from a potentially infected individual before a diagnosis of swine flu is confirmed.

Bonnie Sorensen, chief deputy director of the CDPH, said the disease "has been fairly mild, and like any influenza season, we expect this to last for weeks. As we move along and find out more about this virus, our activities and our responses will change."

As of Tuesday, California health officials will have the capability to test samples of patients believed to have swine flu. Up to Monday, only the US Centers for Disease Control and Prevention in Atlanta had the ability to check for the strain.

Mark Horton, director of the CDPH, said about one-fourth of the federal stockpile of five million courses of vaccines targeting the disease have been sent to Sacramento, capital of California, for possible distribution to local jurisdictions, if needed.

As early as Tuesday, about 625,000 courses of antiviral medication could be made available to Los Angeles County, adding to the current county stockpile of 49,000, said Alonzo Plough, director of the Los Angeles County Public Health Emergency Response.

An additional 1.8 million courses in state and federal reserves could potentially also be made available to the county, he said.

"We have the ability, as this moves forward, to put into place in excess of 2.5 million courses of treatment for people in this county who would be sickened by swine flu," Plough said.

Physicians say that the antiviral treatments should not be taken as a preventative measure, but rather in consultation with a doctor if a patient is suffering from flu-like symptoms. Taking such drugs as Tamiflu and Relenza prophylactically, if they turn out not to be needed, could only make the virus drug-resistant, they say.