April 23 (HealthDay News) -- Seven people in California and Texas have now been diagnosed with a unique form of swine flu, U.S. health officials said Thursday.
All seven people have recovered, Dr. Anne Schuchat, director of the U.S. Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, said during an afternoon teleconference. "So far this is not looking like a very severe influenza," she said.
The patients -- three females and four males -- range in age from 9 to 54, Schuchat said.
The first two cases were reported Tuesday in California. There are now five cases in California, including the father of one of the original patients. The other two cases are near San Antonio, Texas, Schuchat said.
"At this point we don't know the extent of the spread of this strain of human influenza derived from swine," she said. "We don't know exactly how people got the virus. None of the patients have had direct contact with pigs."
People can get the virus without contact with pigs, but that's unusual, Schuchat said. "We believe at this point that human-to-human spread is occurring," she said. "We are likely to find more cases and that will not be surprising."
According to Schuchat, the virus is influenza A N1H1 mixed with swine influenza viruses. The virus contains genetic pieces from four different flu viruses -- North American swine influenza, North American avian influenza, human influenza viruses and swine influenza viruses found in Asia and Europe, she said.
"That particular genetic combination of swine influenza viruses has not been recognized before in the U.S. or elsewhere," Schuchat said.
The viruses are resistant to two antiviral medications -- amantadine and rimantadine -- but are susceptible to the antivirals oseltamivir (Tamiflu) and zanamivir (Relenza), Schuchat said.
Swine flu is a respiratory disease of pigs caused by type A influenza. Swine flu does not normally infect humans. However, human infections do occur, usually after exposure to pigs. Symptoms resemble those of the regular flu, including sore throat, coughing and fever.
CDC investigators are working with health officials in California and Texas to identify the source of the infection and to see if any other people have contracted it, Schuchat said.
The CDC is also asking doctors to be on the lookout for cases of flu that are hard to identify, and send samples of the virus to their state health department. In addition, the CDC is working with the virus to prepare a vaccine should there be a need to produce one against the virus, officials said.
SOURCES: April 23, 2009, teleconference with Anne Schuchat, M.D., director, U.S. Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, Atlanta