Conceptualising access in the direct-acting antiviral era: An integrated framework to inform research and practice in HCV care for people who inject drugs.

As direct-acting antiviral (DAA) therapy costs fall and eligibility criteria are relaxed, people who inject drugs (PWID) will increasingly become eligible for HCV treatment. Yet eligibility does not necessarily equate to access. Amidst efforts to expand treatment uptake in this population, we seek to synthesise and clarify the conceptual underpinnings of access to health care for PWID, with a view to informing research and practice. Integrating dominant frameworks of health service utilisation, care seeking processes, and ecological perspectives on health promotion, we present a comprehensive theoretical framework to understand, investigate and intervene upon barriers and facilitators to HCV care for PWID. Built upon the concept of Candidacy, the framework describes access to care as a continually negotiated product of the alignment between individuals, health professionals, and health systems. Individuals must identify themselves as candidates for services and then work to stake this claim; health professionals serve as gatekeepers, adjudicating asserted candidacies within the context of localised operating conditions; and repeated interactions build experiential knowledge and patient-practitioner relationships, influencing identification and assertion of candidacy over time. These processes occur within a complex social ecology of interdependent individual, service, system, and policy factors, on which other established theories provide guidance. There is a pressing need for a deliberate and nuanced theory of health care access to complement efforts to document the HCV 'cascade of care' among PWID. We offer this framework as an organising device for observational research, intervention, and implementation science to expand access to HCV care in this vulnerable population. Using practical examples from the HCV literature, we demonstrate its utility for specifying research questions and intervention targets across multiple levels of influence; describing and testing plausible effect mechanisms; and identifying potential threats to validity or barriers to research translation.