"It's a wake-up call that we've got to do better," said John Cella, the city's top AIDS official.

The new estimates are part of a broader government strategy to slow the spread of a disease that, while no longer a death sentence, has shown remarkable persistence over decades, foiling health authorities by targeting new groups.

Although AIDS first took root in gay communities, it soon moved on to users of injected drugs. Now, more than half of new infections in Philadelphia are passed through heterosexual contact, a third are the result of men having sex with men, and just 13 percent arise from drug addicts sharing dirty needles, the new federal analysis shows.

"The HIV epidemic is caused by poverty and despair," said Jane Shull, executive director of Philadelphia FIGHT, an AIDS service group.

An estimated 1,400 Philadelphians are newly infected each year - on top of the more than 16,000 who are living with HIV or AIDS - and those who do not realize they have been infected are believed responsible for an outsized portion of new cases.

So public-health workers are testing far more people in far more places, trying to get past cultural barriers that contribute to strikingly high numbers of infections among African American men and fast-increasing rates among black and Hispanic women.

Nationwide, rates of HIV, the virus that causes AIDS, are highest in black communities. Philadelphia has the second-highest percentage of black residents of the 10 most populous cities - 43.2 percent, according to the 2000 census.

Overall, experts said, the local picture is of a disease that is transmitted largely by people who do not think of themselves as being at high risk and have not until recently been primary targets for prevention efforts.

'A tough guy'

"They would think that I was messing around or that I had something already," he said. Plus, "we felt we were true to each other. I did, anyway."

Faison had been living in abandoned buildings until March, when he got into a drug-recovery house in Kensington run by the Fresh Start Foundation. A few weeks later, two counselors from Philadelphia FIGHT came by on their monthly visit offering information and tests for HIV.

"I'm a tough guy," said Faison. "I said 'Me, I'm going to take the test.' "

Twenty minutes later, he learned he was HIV-positive. "I went numb," he said.

HIV tests used to be available mainly through clinics and physicians' offices. Now, they are offered in emergency rooms, city prison intakes, homeless shelters, and mobile units that travel to neighborhoods and social gatherings. All are part of the Philadelphia Department of Public Health's ramped-up efforts during the last year or two to more aggressively target prevention services in minority communities.

The city's new numbers are based on the same 2006 data that caused the U.S. Centers for Disease Control and Prevention in August to raise its national estimate of new HIV infections 40 percent.

There were no comparable estimates to revise locally. But the general profile of the disease in Philadelphia, along with changes in strategy pursued by the CDC nationwide, caused the recent shift in game plan, Cella said.

Public-health workers have few simple, proven prevention tactics to choose from. One is needle exchange, which most experts credit for a steady decline in infections acquired by intravenous drug users sharing dirty syringes.

Rather than trying only to change addicts' behavior, "our main focus is giving people a method where they can remain safe," said Jose Benitez, executive director of Prevention Point Philadelphia, which exchanged more than 100,000 needles last month.

"We don't have that many interventions for other populations," said Kathleen Brady, medical director of the city health department's AIDS Activities Coordinating Office (AACO).

Testing is a powerful prevention tool, and by the end of 2008, Cella expects to have doubled the 30,000 tests typical of previous years.