As Mexico City closed schools and began taking other measures to contain the spread of a swine flu outbreak that might have infected hundreds of people and killed as many as 60, U.S. officials said Friday they had found one new case in San Diego, bringing the total number of U.S. cases to eight.
The most recent victim, a child, has recovered fully - as did all of the other seven victims - said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention. Six of the eight U.S. cases occurred in California's San Diego and Imperial counties and two in Guadeloupe County, Texas.
The cases were identified during routine screening of virus samples, and federal authorities have called for intensified screening of samples from flu victims in the affected areas and from those who recently have traveled to Mexico.
Researchers are concerned about the outbreak because the virus appears to be spread from human to human, which is the crucial requirement for a virus to precipitate a large-scale outbreak.
CDC researchers have so far found no links among the U.S. victims or any common behaviors, Besser said in a conference call, suggesting that there were several intermediaries who passed it among themselves before the virus reached the identified victims.
If that is the case, he added, many people have already been exposed to the virus and it is too late to contain a potential outbreak in the United States. But the good news is that none of the intermediaries appears to have developed serious illness.
None of the American victims has had any contact with pigs, and only one of them has traveled to Mexico recently, he said.
The Pan American Health Organization said Friday that there have so far been 854 cases of "influenza-like illness" in Mexico City, with 59 deaths. An additional 24 cases with three deaths have occurred in San Luis Potosi, in central Mexico, and 24 cases with no deaths in Mexicali, near the U.S. border.