About 34 million people worldwide have HIV, including almost 1.2 million Americans. It's a very different epidemic from the last time the International AIDS Conference came to the United States, in 1990. Life-saving drugs emerged a few years later, turning HIV from a death sentence into a manageable chronic disease for people and countries that can afford the medications.
Yet for all the improvements in HIV treatment, the rate of new infections in the U.S. has held steady for about a decade. About 1 in 5 Americans with HIV don't know they have it, more than 200,000 people who unwittingly can spread the virus.
Government figures show most new U.S. infections are among gay and bisexual men, followed by heterosexual black women. Of particular concern, African-Americans account for about 14 percent of the population but 44 percent of new HIV infections.
Your ZIP code plays a role in your risk, too. Twelve cities account for more than 40 percent of the nation's AIDS cases: New York, Los Angeles, Washington, Chicago, Atlanta, Miami, Philadelphia, Houston, San Francisco, Baltimore, Dallas and San Juan, Puerto Rico. Many are concentrated in specific parts of those cities.
"Maps tell the story," said Brown University assistant professor Amy Nunn, who is beginning a campaign that will bring a testing van door-to-door in the hardest-hit Philadelphia ZIP code.
"It's not just what you do, it's also where you live. There's just a higher chance that you will come into contact with the virus," she explained.
Prospects for a vaccine are so far elusive and health disparities are widening, so why the optimism as expressed by the Obama administration's goal of getting to an AIDS-free generation?
Consider the potential strategies, to add to tried-and-true steps such as condom use and treating HIV-infected pregnant women to protect their unborn babies:
—Studies found treatment-as-prevention could lower an HIV patient's chance of spreading the virus to an uninfected sexual partner by a stunning 96 percent. In the U.S., new guidelines recommend starting treatment early rather than waiting until the immune system has weakened. Abroad, the United Nations hopes to more than double the number of patients being treated in poor countries to 15 million by 2015.
—Other studies show a longtime AIDS medication named Truvada can prevent infection, too, if taken daily by healthy people who are at risk from their infected sexual partners. The U.S. Food and Drug Administration is expected to decide by fall whether to formally approve sale of Truvada as an HIV preventive.
—A study from South Africa found a vaginal gel containing anti-AIDS medication helped protect women when their infected partners wouldn't use a condom, generating more interest in developing women-controlled protection.
—Globally, experts also stress male circumcision, to lower men's risk of heterosexually acquired HIV.
Testing is a key step in improving prevention. The AP-GfK poll found 57 percent of adults say they've been tested at some point, a bit higher than federal estimates, but not enough. The government recommends at least one test for adults, and that populations at higher risk get tested at least once a year.
Following those recommendations depends in part on people's concern about AIDS. The poll found just over half of Americans consider HIV as much or more of a problem now than two decades ago. But less than 20 percent are worried about getting it themselves, and even populations at higher risk don't consider HIV a big threat. Some 16 percent of black respondents said they're very worried about HIV, compared with 4 percent of whites.
"We've become complacent about HIV in America, and it's a real tragedy because hundreds of thousands of people in our own country aren't getting the care they need," said Chris Collins of amFAR, The Foundation for AIDS Research.