An intensive campaign to combat HIV/AIDS with costly antiretroviral drugs in rural South Africa has increased life expectancy by more than 11 years and significantly reduced the risk of infection for healthy individuals, according to new research. The two studies, published Thursday in the journal Science, come as wealthy Western nations are debating how best to stretch limited AIDS funding at a time of economic stress. With an annual price tag of $500 to $900 per patient, antiretroviral therapy programs have stirred frequent debate. Critics argue that adherence to the drug regimen is low and social stigma prevents some from seeking care until they are very ill and have infected others. Cheaper remedies, such as condom distribution, male circumcision and behavior modification, deserve more attention and funding, they say. The new economic analysis of a $10.8-million campaign in KwaZulu-Natal province concluded that the drug scale-up there had been highly cost-effective. The program was administered by nurses in rural health clinics in an impoverished region of about 100,000 people. Treatment consisted primarily of daily doses of antiretroviral therapy, or ART, drugs, which patients take every day for their entire lives. Patients picked up their medication at a rural clinic once a month. In 2003, the year before the drugs were available, 29% of all residents were infected with HIV and half of all deaths there were caused by AIDS. Life expectancy in the region was just over 49 years. By 2011, life expectancy had grown to 60 1/2 years — "the most rapid life expectancy gains observed in the history of public health," said study senior author Till Barnighausen, a global health professor at the Harvard School of Public Health. Based on that increase in longevity, researchers determined just how many years of life were effectively "gained" among residents as a result of ART intervention. They used that figure and the total expense of the program to calculate a cost-effectiveness ratio of $1,593 per life-year saved. The World Health Organization considers medical intervention to be "highly cost-effective" if the cost per year of life saved is less than a nation's per capita gross domestic product. The program's ratio was well below South Africa's 2011 per capita GDP of about $11,000. "It's really a slam dunk of an intervention," said study leader Jacob Bor, a graduate student at Harvard. "These investments are worthwhile." The research team noted that the study period coincided with the arrival of electric power and clean water for area residents. But those alone could not explain the dramatic increase in longevity, they said. "While mortality due to HIV declined precipitously, mortality due to other causes flat-lined," Bor said. "These changes were almost certainly due to ART scale-up." In a second study from the same region, researchers followed nearly 17,000 healthy people from 2004 to 2011 to determine HIV infection rates in areas with active ART intervention programs. Healthy individuals in those areas were 38% less likely to contract HIV than people in areas where ART drugs were not widely available, researchers found. People in extremely rural areas also fared better than those in more closely populated areas clustered around national roads. Overall HIV prevalence increased 6% during the seven years of the study, probably because the antiretroviral drugs allowed people with the virus to live longer, according to the report. It's not clear how the results of the new study would translate to areas where stable, cohabiting couples were not the norm, said lead author Frank Tanser, an epidemiologist at the University of KwaZulu-Natal. AIDS researchers who weren't involved in the studies said they provide strong support for maintaining programs like the President's Emergency Plan for AIDS Relief, begun by President George W. Bush in 2003. "These papers present truly remarkable data," said Dr. Douglas Richman, director of the Center for AIDS Research at UC San Diego.