The White House is closely following the outbreak of a new strain of swine flu in the United States and President Barack Obama has been informed, an administration official said Friday.

The U.S. Centers for Disease Control and Prevention said the virus in the United States was a never-before-seen mixture of viruses typical among pigs, birds and humans. All seven American patients, who came down with the illness, have recovered. But it has also broken out in Mexico, killing at least 16 people and sickening more than 800.

“It is a virus that mutated from pigs and then at some point was transmitted to humans,” Health Minister Jose Angel Cordova said Friday told the Televisa network.

Mexico City has suspended classes at schools and universities to contain what could be a new strain of influenza.

Cordova says private and public schools in this metropolis of 20 million have been ordered to remain closed Friday. The measure could be extended in coming days.

Cordova says the flu is a “new, different strain that can attack anyone.” He says authorities are investigating whether it is related to an influenza strain reported in Texas and California.

The U.S. government said Thursday that seven people had been diagnosed with the new flu in California and Texas.

Dr. Anne Schuchat of the CDC said officials believe it can spread human-to-human, which is unusual for a swine flu virus.

Because of intensive searching, it’s likely health officials will find additional cases, said Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases.

CDC officials detected a virus with a unique combination of gene segments that have not been seen in people or pigs before. The bug contains human virus, avian virus from North America and pig viruses from North America, Europe and Asia.

Health officials have seen mixes of bird, pig and human virus before, but never such an intercontinental combination with more than one pig virus in the mix.

Scientists keep a close eye on flu viruses that emerge from pigs. The animals are considered particularly susceptible to both avian and human viruses and a likely place where the kind of genetic reassortment can take place that might lead to a new form of pandemic flu, said Dr. John Treanor, an infectious disease specialist at the University of Rochester Medical Center.

The virus may be something completely new, or it may have been around for a while but was only detected now because of improved lab testing and disease surveillance, CDC officials said.

The virus was first detected in two children in southern California — a 10-year-old boy in San Diego County and a 9-year-old girl in neighboring Imperial County.

The cases were detected under unusual circumstances. One was seen at a Navy clinic that participates in a specialized disease detection network, and the other was caught through a specialized surveillance system set up in border communities, CDC officials said.

On Thursday, investigators said they had discovered five more cases. That includes a father and his teenage daughter in San Diego County, a 41-year-old woman in Imperial County (the only person hospitalized), and two 16-year-old boys who are friends and live in Guadalupe County, Texas, near San Antonio.

The Texas cases are especially puzzling. One of the California cases — the 10-year-old boy — traveled to Texas early this month, but that was to Dallas, about 270 miles northeast of San Antonio. He did not travel to the San Antonio area, Schuchat said.

The two 16-year-olds had not traveled recently, Texas health officials said.

The swine flu’s symptoms are like those of the regular flu, mostly involving fever, cough and sore throat, though some of the seven also experienced vomiting and diarrhea.

U.S. health officials are consulting with Mexican and Canadian health officials, and the CDC is beginning to receive samples from Mexico for testing, a CDC spokesman said. The ethnicity of the seven confirmed cases was not disclosed.

(Source: Fox News / Associated Press / Reuters)