Key dates in the AIDS epidemic:

— June 5, 1981: The U.S. Centers for Disease Control and Prevention reports five gay men in Los Angeles are suffering from a rare pneumonia found in patients with failing immune systems.

— May 1983: The virus that causes AIDS is identified.

— May 26, 1988: The U.S. government mails "Understanding AIDS," an educational pamphlet to 110 million American homes.

— Aug. 18, 1989: The number of AIDS cases reported in the United States reaches 100,000.

— June 1991: By the 10-year anniversary of AIDS, more than 250,000 Americans have been diagnosed with it and up to 1.5 million more people are infected with HIV.

— Dec. 7, 1995: The FDA approves a new class of drugs for treating HIV, protease inhibitors, a move the government calls some of the most hopeful news in years for AIDS patients. The drugs help transform the disease to a manageable chronic illness.

— Feb. 27, 1997: The government reports a 13 percent drop in AIDS deaths in the first half of 1996, the first significant drop in the epidemic's history.

— Jan. 31, 1999: Researchers report they have convincing proof that the AIDS virus has spread three separate times from chimpanzees to people in Africa — one of the transmissions starting the worldwide epidemic.

— June 2001: At the 20th anniversary of AIDS, the number of Americans diagnosed with the disease tops 700,000. More than 420,000 have died. Worldwide, more than 36 million people are infected with the AIDS virus, with more than 16,000 new infections each day.

— Aug. 23, 2001: The growing scale of the AIDS epidemic in China is acknowledged for the first time by its government.

— Oct. 16, 2001: South African health officials issue a report on the devastating impact of the HIV/AIDS epidemic in that country.

— Nov. 7, 2002: The FDA approves an easy-to-use 20-minute HIV test.

— Jan. 28, 2003: President Bush in his State of the Union address proposes $15 billion in funding in the next five years for emergency AIDS relief in Africa and the Caribbean.

— February 2003: Two big studies find that AIDSVAX, an experimental vaccine made by VaxGen, did not protect against infection with HIV.

— Feb. 17, 2004: A U.N. report warns of the growing AIDS crisis in Eastern Europe and the former Soviet Union.

— March 24, 2004: The FDA approves an oral HIV test that gives results in 20 minutes.

— September 2007: An international test of Merck & Co.'s experimental vaccine is stopped early, because the shots seemed to offer no protection. Further study of the results found potential increased risk of HIV infection among certain men who received the vaccine, although the vaccine itself did not cause infection. A second study also was halted.

— July 2008: UNAIDS estimates the number of deaths worldwide from AIDS in 2007 at 2 million; the number of people living with the AIDS virus is estimated at 33 million. Nearly 7,500 people worldwide become infected each day, UNAIDS estimates.

— Sept. 24, 2009: Researchers say an experimental vaccine — a combination of two previously unsuccessful ones — cut the risk of becoming infected with HIV by 31 percent in a trial of more than 16,000 volunteers in Thailand. But officials caution it likely will be many years before a vaccine might be available.