(AP) -- Swine flu is running wild in the Southern Hemisphere and is spreading rapidly through Europe, with Britain projected to reach 100,000 daily cases by the end of August. The virus is even showing signs of rebounding in Mexico.
World Health Organization Director-General Dr. Margaret Chan and health ministers from around the globe huddled Thursday in Cancun for a two-day summit to design strategies for battling the pandemic. Nations attending include the United States, Canada, China, Britain and Brazil.
"As we see today, with well over 100 countries reporting cases, once a fully fit pandemic virus emerges, its further international spread is unstoppable," Chan said during opening remarks.
Mexican officials wanted the meeting held in the Caribbean resort city of Cancun - where tourism has plunged - to highlight the country's success in controlling its epidemic with a five-day national shutdown of schools and businesses in May.
The measures were applauded by the U.S. Centers for Disease Control and international health officials.
"Our presence here is an expression of confidence," Chan said. "Mexico is a safe, as well as a beautiful and warmly gracious, place to visit."
But Mexico is starting to see an increase in swine flu cases in isolated areas. In southern Chiapas state and the state of Yucatan - adjacent to Quintana Roo state, where Cancun is located - cases have more than doubled in a worrying sign that the country may see a resurgence, especially when its winter flu season begins in November.
In the space of a week ending Tuesday, the number of cases in Yucatan state jumped from 683 to 1,362, and in Chiapas from 492 to 1,079, Mexico's Health Department said. During the same week, Quintana Roo reported 102 new cases.
Yucatan and Chiapas officials blamed the spike on outbreaks in schools, which have since closed a few weeks early for summer break. Mexican Health Secretary Jose Angel Cordova said most of those infected were local residents who had recently traveled to northern Mexico.
"Unfortunately we let our guard down, especially after classes started, and the outbreak is unstoppable," Yucatan Health Secretary Alvaro Quijano told local news media.
Mexico has confirmed a total of 10,687 cases to date, including 119 deaths.
With the Southern Hemisphere in the midst of its winter flu season, Chan said officials are keeping a close watch on those countries. U.S. Health Secretary Kathleen Sibelius said the United States will give 420,000 Tamiflu treatments to the Pan American Health Organization to be distributed in Latin America and the Caribbean.
Chile's epidemic has followed closely behind outbreaks in Mexico and the United States. Cases in the South American country have swelled to 7,342, including 15 deaths. The government has predicted it could see as many as 140 children hospitalized a day.
Argentina, meanwhile, has 1,587 cases and with 26 deaths, ranks third behind Mexico and the United States.
Under mounting pressure, the country's new health minister, Juan Luis Manzur, announced more than $250 million in extra anti-flu funding Wednesday and ordered schools suspended for a monthlong winter break. Health experts consulted by Buenos Aires' leading daily newspaper Clarin estimated that 2.5 million, or 20 percent of people in the capital and its suburbs, could catch the virus.
The city government declared a health emergency this week, along with the provinces of Jujuy and Mendoza, but the federal government has yet to do so.
Mirta Roses, head of the Pan American Health Organization, said a team of 25 experts began working with the South American country this week.
Britain, which has officially reported 7,447 swine flu cases, is the hardest-hit nation in Europe. Many flu experts believe numbers could jump exponentially now that the virus is entrenched.
British officials had been trying to contain the flu by liberally giving out the drug Tamiflu to all suspected victims and their contacts. Health minister Andy Burnham said Thursday that Britain will now only give the antiviral to people with the virus after forecasting 100,000 new swine flu cases a day by the end of August.
Experts questioned Burnham's prediction.
"It seems like a lot of mathematical modeling and not too much common sense," said John Oxford, a professor of virology at St. Bart's and Royal London Hospital.
Oxford predicted swine flu would taper off with summer's warm weather.
Australia has the most cases in the Asia-Pacific region, with more than 4,568 confirmed as of Thursday, an increase of 198 in one day. A 45-year-old man died in the intensive care ward of a Sydney hospital on Monday, becoming the 10th death.
Worldwide, there were 332 deaths and more than 77,000 confirmed cases as of Wednesday, according to the latest figures available from the WHO.
Researchers say they have discovered why outbreaks have been more like a series of local blazes than a wide-raging wildfire.
The new virus has a protein on its surface that is inefficient at binding with receptors in people's respiratory tracts, restricting its ability to spread quickly, according to a report in Friday's edition of the journal Science.
Chan emphasized that most people recover from the illness without medical treatment and most who die have underlying medical conditions. She said researchers may have a vaccine by August but tests to determine its safety would need to be done before making it available to the public.
She also warned that officials are concerned about the virus mutating.
"Like all influenza viruses, H1N1 has the advantage of surprise on its side," she said.
AP Medical Writer Maria Cheng in London and AP Science Writer Randolph E. Schmid in Washington contributed to this report.
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Explore further: Spinach extract could help prevent obesity, study shows