The World Health Organization says the number of officially confirmed swine flu cases worldwide has reached 89,921.

The global body says 12,720 new cases have been reported since Wednesday _ about half of them in the United States.

WHO says Britain, Chile, Mexico, Philippines also reported large numbers of new cases.

Health experts say the number of cases reported to WHO is far below the figure of actual infections because many are mild and never diagnosed.

WHO is working on mathematical models to estimate the real number of infections.

According to the agency's swine flu update Friday, the number of deaths increased by 50 to 382.

Most of the deaths occurred in the U.S.