U.S. health experts said Sunday amid reports that the swine flu is declining in Mexico that they're "cautiously optimistic" the disease isn't as dangerous as first feared -- but that they can't predict if the flu will roar back in the fall.
"The good news is when we look at this virus right now, we're not seeing some of the things in the virus that have been associated in the past with more severe flu. That's encouraging, but it doesn't mean we're out of the woods yet," said Dr. Richard Besser, acting chief of the Centers for Disease Control and Prevention.
With swine flu now in 30 states and counting, authorities say it's still spreading -- but Besser and other health officials said Sunday that the flu in the U.S. has not caused as severe disease as it did in Mexico, where the flu is reportedly waning.
"It's a rapidly evolving situation and it's still one that is cloaked in uncertainty," Besser said. "But each day we're getting more information ... and we're starting to see encouraging signs."
Mexico's health secretary said Sunday the swine flu epidemic in his country "is now in its declining phase," even as the U.S. and five other countries in Europe and Latin America reported new cases. Data in Mexico indicates that shuttering businesses and banning public gatherings nationwide apparently stalled the flu's spread, Health Secretary Jose Angel Cordova said.
The latest tally from the CDC shows 226 confirmed cases across 30 states, up from the 161 cases in 22 states reported on Saturday.
United States Health and Human Services Secretary Kathleen Sebelius said as she and Besser made the rounds on the Sunday talk shows that the country's health officials are "cautiously optimistic" about the flu but that Americans should be aware they could still contract disease.
"We certainly can't get complacent. We need to get prepared," Sebelius said.
The disease could "come back in the fall," Homeland Security Secretary Janet Napolitano said. "It could come back in a more virulent form."
President Barack Obama urged caution Saturday before he met with Mexican President Felipe Calderon to share information about the spread of the flu.
"This is a new strain of the flu virus, and because we haven't developed an immunity to it, it has more potential to cause us harm," Obama said in his weekly address.
The CDC said that most of the swine flu cases have been among older children and young adults. Swine flu has killed one toddler in the U.S. and has spread to 18 countries worldwide — but experts believe the actual spread is much wider.
A new case of the flu was found this weekend at the San Diego State University children's center, where 23 children and staff showed flu-like symptoms. Children under five years of age are considered at especially high risk when they contract the flu.
The global caseload was nearing 800 and growing — the vast majority in Mexico, the U.S. and Canada. Colombia on Sunday reported South America's first confirmed case of swine flu a day after Costa Rica reported the first in Central America.
China quarantined more than 70 Mexican travelers and Hong Kong isolated 350 people in a hotel this weekend as a precaution even though no new swine flu infections appeared in Asia.
The flu hit Europe, too -- the Spanish Health Ministry said the country now has 40 confirmed cases of swine flu, making it the European nation hardest hit by the virus. It said most of the victims have already recovered. All but two had recently visited Mexico.
Britain, Italy and Germany also reported new cases.
Scientists warned that the virus could mutate into a deadlier form as it continues to spread internationally.
"Influenza is unpredictable," said Dr. Tim Uyeki, an epidemiologist at the U.S. Centers for Disease Control and Prevention who has worked on SARS and H5N1 bird flu outbreaks. Uyeki said experts knew very little about the "brand-new" virus and that dealing with its global spread could be a challenge.
Right now, one of the biggest hurdles is a lack of information from Mexico. A team of international and Mexican virus sleuths is trying to piece together an epidemiological picture of who's dying and where transmission began, while also uncovering just how it's attacking people with severe illness -- but details are emerging slowly, and no links have been found between the victims.
The World Health Organization earlier announced that a pandemic was imminent, but it has decided against declaring a full pandemic alert.
The WHO also stressed there was no need for consumers to stop eating pork as long as it's handled properly and cooked thoroughly, as pigs in Egypt and Baghdad were slaughtered amid fear of contracting the disease.
President Obama has asked for $1.5 billion to buy more medicine and equipment if needed to combat the flu.