WHO Declares Swine Flu Pandemic

(CNN) -- The World Health Organization raised the swine flu alert Thursday to its highest level, saying H1N1 has spread to enough countries to be considered a global pandemic.

Increasing the alert to Level 6 does not mean that the disease is deadlier or more dangerous than before, just that it has spread to more countries, the WHO said.

As of Wednesday evening, the virus had spread to 72 countries, the health agency said. There were 25,288 confirmed cases and 139 deaths. The United States had 13,217 cases and 27 deaths, the Centers for Disease Control and Prevention said Friday.

Also Thursday, authorities in Hong Kong ordered the closure of all elementary schools, kindergartens and day care centers in the city after 12 students were found to be infected with the virus.

Authorities have not determined the source of the infection, said Hong Kong's Chief Executive Donald Tsang. This makes it the first cluster of swine flu cases in the city without a link to someone who had traveled overseas.

The number of cases continues to grow in Britain, Japan and Australia -- all of them outside the Americas, where the virus was first detected in April.

Thursday's declaration of a pandemic by the WHO made this the first flu pandemic in 41 years.

In Hong Kong, the schools and day care centers were told to close for 14 days as investigators tried to identify the source of the infection, said Tsang, the chief executive.

The health department will decide after two weeks whether or not to continue the shutdown.

A month ago, Hong Kong quarantined about 300 hotel guests for a week after the first case of the virus was confirmed there.

Hong Kong's abundance of caution stems from the government's unwillingness to see a repeat of the SARS epidemic in 2004, which killed nearly 300 people.

Also on Thursday, Israel's health ministry announced that the number of people diagnosed with swine flu there was 68.

Health officials have begun using the virus' clinical name -- H1N1 -- to reflect that it's actually a combination of several different types of flu and to reduce confusion about whether eating pork can spread the virus. It cannot.