The first measures capable of detecting new HIV cases show that Philadelphians are being infected at a rate more than 50 percent higher than residents of New York City and five times the national average.
"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.
Lester Faison, 50, says he never has had sex with men (including while in prison) or used intravenous drugs (he was addicted to crack cocaine). He never discussed using a condom with either of his last two girlfriends.
"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.
Research suggests that more than a fifth of people infected with HIV are unaware that they have it. The CDC believes that they are likely responsible for a majority of new infections. Other studies show that discovering they are HIV-positive causes most people to dramatically limit behavior that exposes others.
Hence, public-health workers' biggest challenge:
"We need to ask ourselves, 'Where are these folks and how can we reach them?' " said David Acosta, the prevention coordinator for AACO, which funds two dozen independent agencies.
One place is Grays Ferry, a neighborhood that is largely poor, black, and not far from a large gay community in Center City. Infection rates were high, but the area had no testing site. So the city last year started offering HIV screening at a local health center.
To encourage testing among African Americans in the neighborhood, Enon Tabernacle Baptist Church asked its members to come in for HIV tests one day last year. More than 1,000 people lined up, at least half of them from Enon. The event sparked an ongoing AIDS ministry, Associate Pastor Blane Newberry said.
Experts say such innovative approaches are critical for penetrating cultures with barriers to AIDS education.
While activist gay communities, largely white, have been educating themselves about the disease for decades, there is "a lot of hidden homosexuality in black and Latino communities," said Cella, the director of AACO.
Stigma in minority cultures makes it less likely that these men will discuss their secret lives with wives and girlfriends. They then become infected as the epidemic rages in their communities.
"There is no question in my mind that we are seeing a younger population of African American kids with the virus," said Karam Mounzer, medical director of the Jonathan Lax Center, the biggest HIV clinic in the city. "We are also seeing more young African American females."
Another recent pattern, he said, is high numbers of black HIV patients with syphilis. They are far more likely to acquire and transmit HIV and also will get sicker faster.
A CDC analysis last month emphasized the wide disparities in HIV by race, especially for women. Rates for Hispanic women nationally are four times those of white women. Rates for black women are 15 times those of white women.
The new data, based on an additional blood test and a complex algorithm, allow health authorities to separate HIV infections generally from those that are newly acquired.
"Now we have a clearer picture of the leading edge of the epidemic and can target prevention efforts more effectively," said Irene Hall, chief of the CDC's HIV Incidence and Case Surveillance Branch.
The national numbers announced two months ago were projected from data collected by 22 states, including four major cities, said Hall, lead author of the report in the Journal of the American Medical Association.
New York and Philadelphia are the only cities to release their findings so far. Pennsylvania and New Jersey are still analyzing their data.
Infection rates are associated with many factors, from poverty and racial makeup to the effectiveness of prevention efforts. Several officials here complained about cutbacks that amount to an inflation-adjusted loss of 30 percent of federal funding for prevention since 2002.
The structure of Philadelphia and its neighborhoods helps explain the city's rates, said David Metzger, director of the HIV prevention research division at the University of Pennsylvania School of Medicine. It also makes comparisons tricky.
Old cities in the Northeast, for example, tend to have fixed boundaries. Cities such as Atlanta and Houston periodically "annex" surrounding suburbs. While that practice has no effect on who actually gets HIV, it may lower a city's rate - as if, say, Philadelphia were to annex Lower Merion.
Neighborhood structures may actually cause infection to spread faster, said Metzger, who began studying HIV in the late 1970s, before it had a name.
In the mostly poor, black and Hispanic communities with high rates of HIV in Philadelphia, there is a greater chance of coming in contact with the virus "even if you are not doing practices that are considered particularly risky," he said. Once high levels of virus are circulating among the heterosexual population, it is harder to control.
That's how Lester Faison, the recovering crack addict, believes he was infected. And while he hasn't gotten over the diagnosis - the "tough guy" and one-time drug kingpin says he is now afraid to pursue a woman for fear of being rejected - he is taking classes at the Lax clinic, which diagnosed and got him treated for a heart condition he never knew he had.
With the human immunodeficiency virus slowly weakening his immune system, Faison started on anti-retroviral drugs yesterday. But he expects to be around for quite a while.
"The drug use and the way I was living could have killed me," he said. "God brought me out for a reason.
"Maybe this is the reason," he added. "To teach others about HIV and AIDS."