San Francisco’s health department is using medical records and epidemiological tools to map AIDS “hot spots,” areas of the city that have the highest intensity of H.I.V. viral loads and are therefore most susceptible to spread of the disease. The effort is groundbreaking in a number of ways.

 

First, while many communities count the number of H.I.V./AIDS cases in a geographical area, San Francisco uses viral load data – the number of viral particles in patients’ bloodstreams – to track not just where the virus exists but where infection levels are highest and most likely to circulate.

 

This shift is significant, according to a story in last week’s The New York Times, because it might help officials stop transmission of the disease by focusing on “the deepest reservoirs of H.I.V.” It is like moving from the surface of the water to the water’s depths.

 

“We’re taking an individual marker and making it a marker for community health,” said Dr. Grant Colfax, director of H.I.V. prevention and research in the city’s Department of Public Health.

 

Second, the maps provide a credible and actionable fact set that confirms what some had long suspected: In a city with more than 15,000 reported cases of H.I.V./AIDS, the new findings show that the highest viral loads are among African-American, homeless and transgender individuals.

 

“This scientific evidence supports the community’s notion,” said James Loyce, executive director of Black Coalition on AIDS in San Francisco. He noted that some areas of the city have felt “benign neglect,” suspecting that services were geared to the Castro, where more H.I.V.-infected people live.

 

“These hot spots are perpetuating themselves, increasing infection in marginalized communities,” said Dr. Julio Montaner, president of the International AIDS Society and head of the division of AIDS at the University of British Columbia. “As long as we don’t deal with that problem, the reservoir of H.I.V. will ensure that we’re promoting the continued spread of H.I.V. in perpetuity.”

 

Finally, the maps provide something less concrete, though perhaps most valuable: they force us to think beyond previous assumptions and consider completely new possibilities. As noted in the Times’ article, “The city’s decisions on how to act on the new information will be controversial. Officials must decide whether to shift services, create pocketed marketing campaigns or go directly to the individuals with the highest viral load and offer them appropriate care.”

 

“I think we’re asking the right questions,” said Dr. Colfax. “Now the issue is, What are the answers?” Sometimes the best answer to new questions is more new questions.