MEXICO CITY (Reuters) - A strain of flu never seen before has killed up to 60 people in Mexico and has also appeared in the United States, where eight people were infected but recovered, health officials said on Friday.
Mexico's government said at least 20 people have died of the disease in central Mexico and that it may also have been responsible for 40 other deaths.
Mexico reported more than 1,000 suspected cases and four possible cases were also seen in Mexicali, right on the border with California.
The World Health Organization said tests showed the virus from 12 of the Mexican patients was the same genetically as a new strain of swine flu, designated H1N1, seen in eight people in California and Texas.
"Our concern has grown as of yesterday," U.S. Centers for Disease Control and Prevention acting director Dr. Richard Besser told reporters in a telephone briefing.
Global health officials were not ready to declare a pandemic -- a global epidemic of a new and deadly disease such as flu. "So far there has not been any change in the pandemic threat level," Besser said.
But the human-to-human spread of the new virus raised fears of a major outbreak and Mexico's government canceled classes for millions of children in its sprawling capital city and surrounding areas. All large public events like concerts were suspended in Mexico City.
Close analysis showed the disease is a never-before-seen mixture of swine, human and avian viruses, according to the CDC.
Most of the Mexican dead were aged between 25 and 45, a Mexican health official said, in a worrying sign. Seasonal flu can be more deadly among the very young and the very old but a hallmark of pandemics is that they affect healthy young adults.
Mexico has enough antiviral drugs to combat the outbreak for the moment, Health Minister Jose Angel Cordova said.
The WHO said the virus appears to be susceptible to Roche AG's flu drug Tamiflu, also known as oseltamivir, but not to older flu drugs such as amantadine.
"In the last 20 hours, fewer serious cases of this disease and fewer deaths have been reported," Cordova told reporters.
Humans can occasionally catch swine flu from pigs but rarely have they been known to pass it on to other people.
NO CONTAINMENT
The CDC's Besser said it was probably too late to contain this outbreak. "There are things that we see that suggest that containment is not very likely," he said. Once it has spread beyond a limited geographical area it would be difficult to control.
Canada has not reported any cases of the flu and is not issuing a travel warning for Mexico, but the country's chief public health officer David Butler-Jones said the outbreak was "very concerning" and Canada was paying close attention.
The CDC's Besser said it was probably too late to contain the outbreak. "There are things that we see that suggest that containment is not very likely," he said. Once it has spread beyond a limited geographical area it would be difficult to control.
But there is no reason to avoid Mexico, CDC and the WHO said. "CDC is not recommending any additional recommendations for travelers to California, Texas and Mexico," Besser said.
Worldwide, seasonal flu kills between 250,000 and 500,000 people in an average year, but the flu season for North America should have been winding down.
The U.S. government said it was closely following the new cases. "The White House is taking the situation seriously and monitoring for any new developments. The president has been fully briefed," an administration official said.
In California, where six people have been infected with the flu, Governor Arnold Schwarzenegger said authorities were monitoring patients with flu-like symptoms and communicating with Mexican health officials.
Mexico's government cautioned people not to shake hands or kiss when greeting or to share food, glasses or cutlery. Flu virus can be spread on the hands, and handwashing is one of the most important ways to prevent its spread.
The outbreak jolted residents of the Mexican capital, one of the world's biggest cities with around 20 million residents. One pharmacy ran out of surgical face masks after selling 300 in a day.
The virus is an influenza A virus, carrying the designation H1N1. It contains DNA from avian, swine and human viruses, including elements from European and Asian swine viruses, said the CDC, which is already working on a vaccine.
Scientists were trying to understand why there are so many deaths in Mexico when the infections in the United States seem mild, Besser said.
The CDC said it will issue daily updates here
Surveillance for and scrutiny of influenza has been stepped up since 2003, when H5N1 bird flu reappeared in Asia. Experts fear that or another strain could cause a pandemic that could kill millions.
The last flu pandemic was in 1968 when "Hong Kong" flu killed about a million people globally.
(Additional reporting by Stephanie Nebehay in Geneva, Maggie Fox in Washington and David Ljunggren in Ottawa; Writing by Kieran Murray)
April 24 (Reuters) - The U.N. World Health Organization has said it is closely monitoring an outbreak of a new deadly strain of swine flu in Mexico and the United States.
The human-to-human spread of the virus has raised fears of a flu pandemic. The WHO has said it needs more information before it changes its pandemic alert level, currently at three on a scale of one to six. [ID:nLO274836]
Here are some facts about pandemic influenza from the WHO's website here
* Flu pandemics are caused by new flu viruses that adapt into strains that become contagious between humans. [ID:nN24420522]
* Flu pandemics occurred three times in the past century: the Hong Kong flu in 1968, the Asian flu in 1957 and the Spanish flu of 1918. [ID:nN2444047]
* Experts agree that another pandemic could come at any time and could involve any one of a number of new strains of flu. Most eyes have been on the H5N1 strain of avian flu that first infected people in Hong Kong in 1997. Since 2003 it has infected 421 people in 15 countries and killed 257 of them.
* To be declared a pandemic strain, a virus must be new to humans, cause serious illness, be easily transmitted from one person to another, and sustain that transmission efficiently.
* All countries will be affected once a fully contagious pandemic virus emerges. Previous pandemics circled the globe in six to nine months, even before international air travel was common. Today, a virus could reach all continents in weeks.
* Widespread illness will occur. Most people will have no immunity to the pandemic virus. A substantial percentage of the world's population will need medical care, but few countries have enough staff, facilities, equipment and hospital beds.
* Supplies of vaccines and antiviral drugs will be inadequate. Many developing countries will have no access to vaccines.
* Many people will die. Based on the 1957 pandemic, the WHO conservatively estimates 2 million to 7.4 million people may die during the next outbreak, but says all estimates are speculative, and will depend on how many people become infected and the virulence of the virus, among other factors.
* Economic and social disruption will be great. High rates of worker absenteeism will impair services like power, transportation and communications.
* Every country must be prepared. The WHO has issued a series of recommended responses to the pandemic threat.
* The WHO will alert the world when the pandemic threat increases, working closely with governments and public health organizations on surveillance. WHO experts say it is too soon now to declare another pandemic. (Reporting by Roberta Rampton; Editing by Maggie Fox and Will Dunham)
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