SATURDAY, April 25 (HealthDay News) -- Mexican authorities continued to take dramatic steps Saturday to try to contain the swine flu outbreak that has killed as many as 68 people, and sickened more than 1,000 others.

In the United States, two new cases were reported Saturday by health officials in Kansas, as well as a new case in California, bringing the national total to 11, according to the Associated Press. Eight more cases of "probable" swine flu involving school students have been identified by New York City health officials. Cases in the U.S. have so far remained mild.

Dr. Anne Schuchat, the U.S Centers for Disease Control and Prevention's Interim Deputy Director for Science and Public Health Program, told reporters on Saturday that her agency was "worried, and because we are worried we are acting aggressively on a number of fronts" to investigate the outbreak. She added that, because of the wide geographic spread of the virus so far, the outbreak is already "beyond containment."

But Schuchat added that U.S. health officials had numerous tools to fight the illness' spread and protect the health of Americans.

Earlier in the day, the head of the World Health Organization said that the outbreak has the potential to develop into a pandemic.

WHO Director-General Margaret Chan said the outbreak involves "an animal strain of the H1N1 virus, and it has pandemic potential." But, she added, it was too early to say whether a pandemic would occur, the Associated Press reported.

Twenty-four suspected new cases of swine flu were reported Saturday in Mexico City alone. The government ordered schools closed and all public events have been suspended for the time being, including more than 500 concerts and other gatherings in the city of 20 million residents, the AP said.

The WHO has advised countries around the world to look for similar outbreaks.

All of the original eight patients in the United States -- six from California and two from Texas -- have recovered from their infections. According to the AP, Kansas health officials say that the two new cases there, involving a married couple, were also mild. The newly identified case in California involves a 35-year-old woman who was hospitalized but has recovered.

Speaking to reporters in a Saturday afternoon teleconference, the CDC's Schuchat said that "at present there are still eight confirmed human cases of swine influenza in the United States. There is a serious situation in Mexico with severe disease and a number of confirmed swine influenza infections, generally among adults." She stressed that "these are very dynamic times and many things will be changing," and the spread and severity of the virus would be "very hard to predict."

While agents at the Border Infectious Disease Surveillance system at the U.S.-Mexico border are on high alert for those who might be carrying the flu, containing the virus was probably out of the question, Schuchat said. "If we found only a new influenza virus in one place, in a small community, we might be able to quench or contain it. But with infections in many different communities as we're seeing, we don't think that containment is feasible," she said. She added that as investigators probe deeper into cases in cities away from California and Texas, new cases are likely to emerge.

But Schuchat stressed that there are other ways to fight the flu. "Containment would be fantastic, but we think that there are many, many tools in our toolbox to reduce the illness and suffering that this virus is causing, and reduce transmission -- even if we are not in a circumstance where we could contain it," she said.

Schuchat added that steps are already being taken to devise a vaccine against this strain of swine flu, although the process takes time. "We are taking the initial steps in terms of preparing the seed virus to hand off to the industry partners, to produce large quantities. But you know it takes months to produce a vaccine," she said.

CDC officials said Friday that tests showed some of the Mexico victims died from the same new strain of swine flu that sickened the eight people in Texas and California. It's a worrisome new strain that combines genetic material from pigs, birds and humans.

"The United States government is working with the World Health Organization and other international partners to assure early detection and warning and to respond as rapidly as possible to this threat," Dr. Richard Besser, acting director of the CDC, said during a Friday afternoon press briefing.

Besser said the CDC issued an outbreak notice for travelers to central Mexico and Mexico City, alerting people to the flu outbreak. "At this time there are no recommendations for U.S. travelers to change, restrict or alter their travel plans to Texas, California or Mexico," he said.

While Mexico's flu season is usually over by now, health officials noticed a sizeable uptick in flu cases in recent weeks. The World Health Organization reported about 800 cases of flu-like symptoms in Mexico in recent weeks, most of them among healthy young adults, with 57 deaths in Mexico City and three in central Mexico, The New York Times reported Friday.

That could be worrisome. Seasonal flus usually strike hardest at infants and the elderly, but pandemic flus -- such as the 1918-19 Spanish flu, which killed an estimated 20 million to 40 million people worldwide -- often strike young, healthy people, the newspaper reported.

Schuchat said Thursday that the virus in the United States 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 found in the United States 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.

Dr. Marc Siegel, associate professor of medicine at New York University School of Medicine, said the current outbreak was unlikely to become a pandemic. "Swine flu could cause the next pandemic, but it is not likely that this thing is going to erupt and take over the world," he said. Even though the virus is being transmitted human-to-human, "that's a far cry from becoming a pandemic," he added.

Dr. Martin J. Blaser, chairman of the Department of Medicine at New York University Langone Medical Center in New York City, also believes it's unlikely the outbreak will trigger a pandemic.

"The CDC has been doing more surveillance for flu," Blaser said. "So it could be that these cases have been happening all the time, but we just never saw them. Or it is possible that it is a new strain of influenza that is emerging or it's a dangerous new combination. That's why we have to watch it closely."

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