AIDS is often part of an overlapping cluster of epidemics. AIDS cases are increasingly concentrated in disadvantaged populations that have high rates of poverty, homelessness, unemployment, and inadequate access to health care. AIDS also overlaps with other illnesses, including drug addiction, mental disorders, sexually transmitted diseases (STDs), tuberculosis (TB), and hepatitis. These conditions may contribute to the risk of HIV exposure and transmission and may complicate HIV prevention and therapeutic efforts.
AIDS has had a disproportionate impact on the poor and disadvantaged populations. Over the course of the epidemic, there has been a steady increase in the numbers of HIV-infected persons who are homeless and marginally housed (Bangsberg et al., 2000; Zolopa et al., 1994). Many of these individuals lack access to necessary health services, including primary medical care, substance abuse treatment, and HIV care (including treatment with new antiretroviral therapies) (Acuff et al., 1999). Recent studies suggest that poverty contributes to HIV infection risk in several ways. Socioeconomic instability may contribute to higher rates of prostitution, drug use, incarceration, and family disruption, all of which are linked to the spread of HIV (Fournier and Carmichael, 1998).
The link between substance abuse and risk of HIV infection is well-established (IOM, 1997; NRC and IOM, 1995; NRC, 1989). Injection drug users are primarily infected through sharing of contaminated injection equipment, which acts as a vector for HIV-infected blood (NRC and IOM, 1995). HIV infection among injection drug users also poses a threat to their sexual partners and children (NRC and IOM, 1995). Use of non-injection drugs (e.g., alcohol, crack cocaine, methamphetamines, and inhalants) also can impair decision-making, thereby increasing the likelihood of HIV transmission and infection through high-risk behaviors (e.g., unprotected sex or trading sex for drugs) (IOM, 1997). Immunosuppression caused by long-term use of alcohol and drugs increases the likelihood of infection and, among infected persons, increases the development of AIDS-related opportunistic illnesses (Acuff et al., 2000).
Mental illness also can increase HIV infection and transmission risk (Diamond and Buskin, 2000; Marks et al., 1998). Although some mental disorders may exist prior to the HIV diagnosis (e.g., depression and personality disorders), others may develop during the course of the disease (e.g., HIV-associated dementia). Serious mental illness increases the likelihood of high-risk sexual behaviors or substance abuse, and thus may contribute to treatment nonadherence. Individuals with severe and persistent mental illness (e.g., schizophrenia) often experience high rates of unemployment, poverty, and homelessness, which can increase the com-