Patterns of drug use and abuse among aging adults with and without HIV: A latent class analysis of a US Veteran cohort

Abstract

This study characterized the extent and patterns of self-reported drug use among aging adults with and without HIV, assessed differences in patterns by HIV status, and examined pattern correlates. Data derived from 6351 HIV-infected and uninfected adults enrolled in an eight-site matched cohort, the Veterans Aging Cohort Study (VACS). Using clinical variables from electronic medical records and socio-demographics, drug use consequences, and frequency of drug use from baseline surveys, we performed latent class analyses (LCA) stratified by HIV status and adjusted for clinical and socio-demographic covariates. Participants were, on average, age 50 (range 22–86), primarily male (95%) and African-American (64%). Five distinct patterns emerged: non-users, past primarily marijuana users, past multidrug users, current high consequence multidrug users, and current low consequence primarily marijuana users. HIV status strongly influenced class membership. Non-users were most prevalent among HIV uninfected (36.4%) and current high consequence multidrug users (25.5%) were most prevalent among HIV-infected. While problems of obesity marked those not currently using drugs, current users experienced higher prevalences of medical or mental health disorders. Multimorbidity was highest among past and current multidrug users. HIV-infected participants were more likely than HIV-uninfected participants to be current low consequence primarily marijuana users. In this sample, active drug use and abuse were common. HIV-infected and uninfected Veterans differed on extent and patterns of drug use and on important characteristics within identified classes. Findings have the potential to inform screening and intervention efforts in aging drug users with and without HIV.

Introduction

Drug use among older adults in the US is occurring at unprecedented high levels and growing. The baby boom generation (i.e., people born 1946–1964) has higher prevalences of lifetime drug use compared to all previous generations and appears to be continuing their drug use later into life (Han et al., 2009a). In 2007, all adults aged 50–59 were baby boomers; recent national data reveal that in the same year the prevalence of self-reported past year illicit drug use in this age group nearly doubled from 2002 figures (Han et al., 2009b). Updated projections forecast that by 2020, the number of adults 50 or older with substance use disorder will more than double from 2.8 million in 2002–2006 to 5.7 million (Han et al., 2009b), a projection 30% higher than previously estimated (Colliver et al., 2006, Gfroerer et al., 2003). The enormity of this problem is compounded by under-recognition of substance use in older people (Levin and Kruger, 2002), limited data on the types and patterns of their drug use (Levy, 1998, Lieberman, 2000), the lack of substance abuse treatment services for older adults (Office of Applied Studies, 2007), under-utilization of screening tools for primary care practitioners to identify substance abuse problems (Friedmann et al., 2001, Kim et al., 2007, Lewis, 1997), and the medical and psychological comorbidities that often accompany and complicate the health status of older drug users (GMHF, 2010, Reid and Anderson, 1997, Reid et al., 2002, Simoni-Wastila and Yang, 2006).

At the same time, HIV is increasingly affecting older populations because HIV-infected persons are living longer on more effective treatments while HIV incidence in this age group is on the rise. Approximately 10% of new HIV infections in the US occur among people over 50 years of age (Centers for Disease Control and Prevention, 2008). Drug use, especially by injection, is one of the primary modes of HIV and hepatitis transmission, and thus one might expect HIV-infected older adults to have higher prevalences of injection drug use (IDU) compared to their uninfected peers. On the other hand, HIV incidence among IDUs has declined by 50% or greater over the past 20 years (Des Jarlais et al., 2000, Lee et al., 2003), and, in many places, HIV transmission among IDUs has been associated with sexual transmission rather than unsafe injection (CDCP, 2009, Kral et al., 2001, Strathdee et al., 2001). Furthermore, most illicit drug use in the US is non-injection (Substance Abuse and Mental Health Services Administration, 2009). Regardless of HIV status and transmission category, patterns of current drug use are poorly understood in older adults (Rabkin et al., 2004, Rosenberg, 1995, Schlaerth, 2007).

The nexus of these three issues – drug use, HIV, and aging – is an understudied yet looming problem. Evidence suggests that HIV may speed aging and exacerbate problems of older age. Active drug use contributes to poor health outcomes for people with and without HIV alike (AETC, 2006, Bruce et al., 2008, Kapadia et al., 2005), and may be particularly harmful if addictive disorders persist later in life. Older adults with HIV may thus be disproportionately burdened by the negative consequences of ongoing drug abuse (Zanjani et al., 2007). For example, both older age and HIV infection are risk factors for unintentional fatal drug overdose (Darke and Zador, 1996, Tardiff et al., 1997, Wang et al., 2005). Biological mechanisms of this elevated risk may be due to changes in metabolism and body water content in older adults that can lead to higher serum drug concentrations over prolonged periods, thereby increasing risks of unintentional injuries such as drug overdose.

Few studies have been conducted with sufficient power to contrast drug use by HIV status and age; even fewer provide generalizable data (Levy, 1998, Lieberman, 2000) or detailed information regarding medical and psychiatric comorbidities related to substance use problems. One study, limited by sample size, found that lifetime drug dependence was higher for the HIV-infected than uninfected individuals, and that expected age-associated declines in diagnoses of dependence were not detected among the HIV-infected (Rabkin et al., 2004). Analysis of data from a larger, more diverse sample is needed to assist clinicians and policy makers in developing evidence-based responses to changing patterns of drug use in aging populations.

In this paper, we used data from the Veterans Aging Cohort Study (VACS) (Justice et al., 2006a), a longitudinal, prospectively consented, observational cohort study conducted among HIV-infected Veterans and age-, race- and site-matched HIV uninfected controls receiving medical care at one of eight US Veterans Administration (VA) facilities to: (1) characterize patterns of self-reported drug use in a large and diverse cohort of aging HIV-infected and uninfected US Veterans and analyze their construct validity; (2) assess pattern differences by HIV status; and (3) describe demographic, medical and psychiatric pattern correlates within this population. To accomplish these aims, we employed latent class analysis (LCA) (Agrawal et al., 2007, Lubke and Muthen, 2005, Muthen, 2006) to identify patterns of behavior, using all available baseline VACS information. We chose this empirical approach to minimize the potential for measurement error, bias, or oversimplification (Kapadia et al., 2005) inherent when a priori definitions are used to aggregate and categorize complex behaviors.