Across Philadelphia, people often don't find out they have HIV until the infection has already progressed to AIDS.

About 15 out of every 100,000 people in the Philadelphia metropolitan area received an initial diagnosis of AIDS, also known as Stage 3 HIV. That rate of late-stage diagnoses is about 50 percent higher than the national average, according to data from the U.S. Centers for Disease Control and Prevention's 2011 HIV surveillance report.

Those with AIDS have likely been living with the virus for many years. HIV prevention activist Luke Messac said years without treatment increase the chances someone will experience immune-system damage or spread the virus to others.

"One thing you have to consider is: How do most people come to realize they have HIV? It's through their physician," said Messac, a third-year medical student at the University of Pennsylvania.

Covering more people with health insurance could boost HIV testing and the chances for early detection and treatment, Messac said. A member of Act Up Philadelphia, Messac wants Gov. Tom Corbett to expand Pennsylvania's Medicaid program through the federal health law.

Messac says smart government policies can reduce the number of people without health insurance coverage and improve health-care choices in low-income communities.

"These things all prevent people from getting to the doctor when they need to," Messac said.

Health advocates are pushing for more routine HIV testing for lots of reasons -- including a hope to detect and treat infection before it progresses to AIDS.

Door-to-door testing effort

Researcher Amy Nunn, an assistant professor of medicine at Brown University, is leading a door-to-door HIV testing campaign in Philadelphia's 19143 ZIP code. That neighborhood in Southwest Philadelphia has the city's highest rate of HIV infection.

Her efforts have also helped expand testing access at a nearby health center, the Health Annex.

Every patient who walks through the clinic door now qualifies for an HIV test, and the electronic-records system now has pop-up notices that remind medical personnel to suggest screening to everyone.

"Before only people that were perceived to be at high-risk were offered HIV testing in general," Nunn said. "Now we are trying to move away from that and towards offering everyone a test."

Nunn said increasing access to testing is just one part of her effort. Her group asked Philadelphia clergy to support HIV testing and then launched a social marketing campaign featuring pastors and other religious leaders. 

"You can't just offer testing and expect, overnight, that thousands of people will step up and say yes," Nunn said. "We're trying to stimulate demand and normalize testing and treatment."

Nunn said treatment is an important prevention strategy.

"If we treat people, the chances that they transmit the virus to others are reduced by about 96 percent," she said.