WEDNESDAY, June 18 (HealthDay News) -- While older adults may seem the least likely group of Americans to become infected with HIV, a new study suggests it would be cost-effective for doctors to routinely give AIDS tests to some sexually active people in their 60s and 70s.

In fact, an HIV diagnosis and subsequent treatment could potentially add an average of six to nine months to an older person's life, said study co-author Dr. Douglas K. Owens.

"Just because you have someone who's older doesn't mean you shouldn't think about HIV and HIV screening," said Owens, a senior investigator at the VA Palo Alto Health Care System in California and professor of medicine at Stanford University.

Older Americans have been largely overlooked throughout the years of the AIDS epidemic, although they are hardly immune. The federal government only recommends routine HIV testing up until the age of 64.

Still, an estimated 20 percent of HIV patients are older than 50, Owens said. And research with older veterans has suggested that as many as one in 200 is infected with the virus that causes AIDS, he said.

The AIDS threat facing older Americans is often ignored, because "people find it difficult to imagine their parents and grandparents being sexually active," said Rowena Johnston, vice president of research with the Foundation for AIDS Research.

For the new study, published in the June 17 issue of the Annals of Internal Medicine, Owens and his colleagues created a mathematical formula to determine the costs and benefits of routinely testing people aged 55 to 75.

The researchers found that it's cost-effective to test people in that age group if the prevalence of undiagnosed HIV infection is greater than 1 in 1,000 and those being tested have sexual partners at risk of infection.

They reported it may cost $30,000 in tests to lengthen a sexually active 65-year-old person's life by something known as a "quality-adjusted life year," a complicated measurement that takes into account the difficulty of life during illness. On average, diagnosing a 65-year-old with HIV instead of allowing him to remain untreated could lengthen his life by six to nine months, Owens said.

"That's actually a lot. That's a pretty big change," he said. "Many of the interventions we do change life expectancy by a week, a few weeks, maybe a month."

AIDS tests typically cost from $10 to $70, Owens said.

Johnston said doctors with older patients "should to be aware they may be carrying their own biases. It's worth taking into account the person's sexual history and whether they have risk factors."

Still, some observers may question the study's assumption that more than one in 1,000 older adults have HIV and are undiagnosed, said Frank Myers, director of clinical epidemiology and safety systems at Scripps Mercy Hospital in San Diego.

"This study, with its assumptions of HIV prevalence, will not be enough to change HIV screening recommendations by itself," Myers said. But, he added, he hopes the research will motivate health-care providers to ask patients about HIV risk factors and target them with messages about prevention.

More information

For more about older adults and AIDS, visit the Foundation for AIDS Research.