In California, Cases Suggest Border Origin

SACRAMENTO, Calif. -- Doctors tracking swine flu in this state are investigating a new theory: What if it didn't originate in Mexico but instead had been floating around the border region for months?

Growing evidence in California suggests that early flu cases had no apparent origin in Mexico. Many of the early California victims -- including the first two cases -- say they hadn't traveled to Mexico and had no contact with pigs. Some may have fallen ill before the first Mexicans did.

Those cases contradict the conventional understanding of how the strain originated. They could also offer important clues about the future trajectory of the disease. Other cases here and in other states, as well as abroad, have clear links with Mexico.
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But the outbreak in California may have a separate origin. "This virus has been circulating around in the population for some time," said Gilberto Chavez, an epidemiologist with the California Department of Public Health. Its similar symptoms to a standard flu, he said, meant that "any cases that might have been around were probably seen, treated and diagnosed as regular flu."

Michael Shaw, associate director for laboratory science for the influenza division of the Centers for Disease Control and Prevention, said the flu theoretically could have appeared first in California, but he cautioned against drawing any conclusions since the strain also exhibited genetic characteristics traceable to Eurasia.

The first case discovered in California was a 10-year-old boy in San Diego County, who fell ill with a fever March 30.

Health authorities stumbled upon the case by chance. The boy had a throat swab taken at a clinic during a random check, a common procedure by health officials to monitor illness around the U.S.-Mexico border. "We got lucky," said Mr. Chavez.

Tests revealed the flu virus didn't match any typical human flu subtype. The CDC received samples April 14 and determined the cause to be the now well-known A/H1N1 influenza.

By the time state and federal epidemiologists reached the family, the boy had recovered.

The second case was a 9-year-old girl in neighboring Imperial County who was treated for a cough and a 104-degree fever March 28; her cousin had fallen ill three days earlier. On April 1, the girl's brother fell ill, too. "We found absolutely no contact with swine," said Paula Kriner, an epidemiologist with the county health department. Tests confirmed on April 17 that the girl had the new strain.

One possible scenario is that swine flu had been spreading around the U.S.-Mexico border during the winter flu season with few symptoms, then evolved into a more serious form with fever and a cough.

That means the more serious cases could "only be the tip of the iceberg" said Robert Kim-Farley, a professor and epidemiologist at the University of California at Los Angeles School of Public Health. And should a version with few symptoms exist -- in California or elsewhere -- it could be spreading undetected, he said.

"The trajectory of influenza can be unpredictable," said Lisa Winston, an epidemiologist with the University of California at San Francisco Department of Medicine, Infectious Diseases Division. "If there are a lot of people who had already been infected and they did well, it suggests that this wave in the U.S. might not be so bad. But we don't have clear evidence to say that yet."

State health officials raised the possibility that the California strain is different from the one in Mexico. But Mark Horton, the state's lead epidemiologist, said, "We're still confidently calling it the swine flu."