“We talk about generalized epidemics and concentrated epidemics,” said Dr. Kevin M. De Cock, director of global health at the Centers for Disease Control and Prevention in Atlanta.

“As guidance, we say if the prevalence of H.I.V. is greater than 1 percent in a sentinel population like pregnant women, we call it a generalized epidemic,” he added. “That is terribly arbitrary, but useful for certain discussions.”

Because the conferences, held every two years, offer one of the biggest lobbying venues for AIDS workers, pleas for money from governments, foundations and other sources are standard. Indeed, the conference in South Africa in 2000 is credited with stimulating efforts to provide access to antiretroviral drugs for millions of people in poor countries who would have otherwise died.

Many participants were disappointed that President Obama did not appear. But a large number of administration officials, members of Congress and Bill Clinton did attend.

This conference came at a time of global recession, which has reduced the financial contributions used to provide treatment to those who need it. Of the 15 million infected with H.I.V. only five million are receiving the drugs they need, according to U.N.AIDS.

At the same time, participants raised questions about the ethics of providing uninfected Americans with drugs to prevent H.I.V. when poor people elsewhere with AIDS received none.

Many participants likened ending the AIDS epidemic to medicine’s successes against two other viral infections, smallpox and polio. Smallpox is the only naturally occurring human infection to have been eradicated, meaning that cases can no longer arise because the causative virus has been wiped out of nature.

The World Health Organization defines elimination of an infectious disease as bringing the number of cases below a predetermined amount, or reducing the number to zero in a specific region. Polio was eliminated from the Western Hemisphere, though it requires regular controlled public health efforts to maintain that, and it still is spread in Nigeria, Afghanistan and Pakistan.

The conference participants who spoke of eradicating or eliminating AIDS failed to recognize that a vaccine was required to succeed against smallpox and polio.

In saying that the United States is committed to achieving an AIDS-free generation, Secretary of State Hillary Rodham Clinton told the conference that her definition of the phrase means “virtually no child anywhere will be born with the virus” by 2015. People who become infected “will have access to treatment that helps prevent them from developing AIDS and passing the virus on to others.”

Under Mrs. Clinton’s definition, many people will continue to become H.I.V.-infected, but not go on to suffer the myriad other infections and devastation caused by AIDS. “The disease that H.I.V. causes need not be with us,” she said.

But even if that goal is reached, millions will be living with H.I.V. for a long time to come.

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By LAWRENCE K. ALTMAN, M.D.