Networks, resources and risk among women who use drugs

Abstract

The public health tradition of intervening at the environmental level has not been fully exploited in terms of HIV prevention efforts among drug users. Women who use drugs are at particularly high risk of acquiring HIV and other blood borne and sexually transmitted infections, such as hepatitis B (HBV) and hepatitis C (HCV), and could potentially benefit from environmental level interventions. In a review of the existing literature, we examine the extent to which the linkages among multiple causal levels may contribute to the disease transmission risk experienced by women who use drugs. The multiple causal levels of risk potentially involved in the transmission dynamics of infectious pathogens include biological, behavioral, dyadic relationship, network, and structural levels. Biological and behavioral risk factors have already been examined in depth; yet, little empirical research currently exists for other causal levels. Increasingly, investigators suggest that the character and dynamics of relationships with sex partners may be an important determinant of risk, both for engaging in risk behaviors and for doing so with high-risk partners. The influence of higher-order causal level factors, specifically network and structural factors, are the least well documented, but are posited to be a principal underlying cause of the current differential HIV incidence rates between men and women who use drugs. Future research should focus on these higher-order causal levels, in order to better understand disease transmission dynamics; to better evaluate the limitations, as well as the opportunities, of current intervention efforts; to develop interventions that improve and supplement current HIV prevention efforts among women who use drugs; and to inform public policy debate.

Introduction

After several decades in which technological advances in epidemiologic method and biochemistry have facilitated the study of individual level disease risk factors, researchers are once again turning their focus to environmental factors as an integral part of public health discourse (Rothman, Adami & Trichopoulos, 1998; Schwartz, 1994; Susser, 1998; Susser & Susser, 1996). Investigators have recently begun to apply this discourse in an effort to better understand environmental contributions to the HIV/AIDS epidemic (Aggleton, O’Reilly, Slutkin & Davies, 1994; Mann, 1991; Rhodes et al., 1999; Zierler & Krieger, 1997); however, the public health tradition of intervening at the environmental level has not been fully exploited in terms of HIV prevention.

While it is not clear that interventions at the environmental level can impact HIV risk behaviors at the individual level, it is important to examine and document relationships at multiple levels in order to: (1) better understand disease transmission dynamics; (2) develop interventions based on both a theoretical and practical understanding of the limitations and opportunities inherent in implementing prevention at any one level; and (3) improve the ability to evaluate interventions designed to intervene at either one specific level (e.g., the individual in most cases), or at multiple levels, (e.g., the diffusion of innovation, which is designed to alter group behavioral norms such that individuals no longer participate in risk behaviors). The following is a review of the existing literature that examines the multiple levels that may contribute to women's increased risk of acquiring infectious pathogens, including HIV, with a particular focus on research conducted with women who use drugs in the United States (US).

Women who use drugs (i.e., heroin, crack and/or cocaine), through either injected or non-injected routes of administration, are at high risk of acquiring HIV and other blood borne and sexually transmitted infections, such as hepatitis B (HBV) and hepatitis C (HCV) (Holmberg, 1996; Irwin et al., 1996; CDC (1998), CDC (1996)). These women are at higher risk of becoming infected with these pathogens than are women who do not use drugs and may be at higher risk than men who use drugs, particularly during the period soon after initiation of injecting drug use (Des Jarlais et al., 1999; Fennema, van Ameijden, van den Hoek & Coutinho, 1997; Garfein, Vlahov, Galai, Doherty & Nelson, 1996).

HIV infection among women who use drugs may be diagnosed at a later stage in disease progression than among men (Chaisson, Keruly & Moore, 1995; Schoenbaum & Webber, 1993). Consequently, the rate of progression to AIDS may be faster and the probability of treatment with antiretroviral therapy lower among women than among men. The lack of early identification of HIV infection status among women may be linked to higher levels of morbidity and mortality. HCV is an equally serious disease whose sequelae include cirrhosis of the liver and hepatocellular carcinoma; between 60 and 80% of HCV infected individuals are also chronic carriers of the virus (CDC, 1996; Alter & Moyer, 1998). Currently, there is no vaccine or effective cure available. A very high seroprevalence of HCV has been documented among diverse groups of drug injectors worldwide, with women injecting drug users as likely as men injecting drug users to be infected (MacDonald, Crofts & Kaldor, 1996).

In addition to experiencing a high risk of acquiring infectious pathogens, women who use drugs are at increased risk of transmitting HIV, HCV and infectious HBV to their infants, and may be vectors of transmission to their sex or drug injecting partners. Given the ability of antiretroviral therapies to reduce viral load and, potentially, disease transmission capabilities (Carpenter et al., 1996; Miller, 1999a), early identification of infection among women is warranted. More importantly, however, is the need to prevent a high rate of infection with HIV, as well as with HBV and HCV, among women who use drugs.

In order to prevent infection with HIV, as well as with HBV and HCV, among women who use drugs, and to prevent them from transmitting these viruses to their infants and their drug use or sex partners, the factors that increase women's risk of acquiring these infections need to be determined. The factors that increase women's risk may occur at different causal levels. Knowledge about the different causal levels may be used to identify different points of intervention to disrupt disease transmission. For clarity, the multiple causal levels that are potential risk factors for the transmission of infectious pathogens are reviewed separately. However, it is important to recognize that these levels interact with one another, although one or more levels may be dominant depending on the type of risk involved (e.g., the probability of engaging in commercial sex may be increased by differential access to employment). Examples are provided where linkages become more complex.