Many of the illnesses common among older people are related to the aging process. As people age, their bodies aren't able to repair and rebuild damaged cells (organs, tissues) as rapidly as those of younger people. So, what does this mean for older adults with a disease like HIV that attacks and destroys the body's defenses (CD4 and CD8 cells)? HIV-positive older adults are more likely to have additional medical problems like diabetes and high blood pressure, and more physical limitations than younger adults with HIV. In the early years of the HIV epidemic (before HAART), older adults' health deteriorated more rapidly than that of younger individuals -- regardless of CD4 count. Several studies found that older adults had lower CD4 counts at diagnosis, faster progression to an AIDS diagnosis, more opportunistic infections, and a shorter survival rate than younger adults, regardless of when they were first diagnosed with HIV.

Recent studies have found that a person's age doesn't interfere with the ability of HAART to reduce viral load, but there may be differences between younger and older people in how well the immune system responds to treatment. A study published in AIDS (2000) by Roberto Manfredi and Francesco Chiodo in Bologna Italy examined the effect of HAART on older people (defined as 55 or older) compared to younger people (35 or younger). The study included 21 older people (8 women, 13 men) and 84 younger people (29 women, 55 men). The researchers found that both groups responded to HAART, especially in reducing viral load. However, CD4 counts did not increase as much in the older people relative to the younger ones. On average, CD4 counts increased from 212 to 289 for older adults after one year of HAART. During the same period, CD4 counts rose from 231 to 345 for younger people.

Some people may have a very low CD4 count even though they have an undetectable viral load. This may be related to decreased activity in the thymus (the gland where CD4 cells are made). A 2001 study in AIDS conducted by researchers in Los Angeles included 80 HIV-positive veterans (13 were over 55 and 67 were younger). Although both groups of veterans showed dramatic reductions in viral load once they were on treatment, the researchers found significant differences in CD4 levels at 3, 9, 15, and 18 months. After one year on HAART, average CD4 counts increased by 50 for the older men, compared to increases of 100 for the younger ones. This difference was not related to baseline HIV viral load, coinfection with hepatitis C, or the race/ethnicity of participants.

Patients who have significantly lower viral loads but who don't have increases in CD4 counts shouldn't necessarily be considered (or consider themselves) treatment failures. These results should affect decisions about when to begin treatment and what preventive medications to use to reduce opportunistic infections as well as when evaluating treatment success for older people. These studies represent an important first step in understanding how their age may affect older adults' response to HIV treatment, but more studies are needed to understand the long-term effects of age on HAART in older adults. This research is becoming more important as the HIV population ages and the number of new infections in older adults remains high.