PURPOSE OF REVIEW

Differentiated service delivery (DSD) models were initially developed as a means to combat suboptimal long-term retention in HIV care, and to better titrate limited health systems resources to patient needs, primarily in low-income countries. The models themselves are designed to streamline care along the HIV care cascade and range from individual to group-based care and facility to community-based health delivery systems. However, much remains to be understood about how well and for whom DSD models work and whether these models can be scaled, are sustainable, and can reach vulnerable and high-risk populations. Implementation science is tasked with addressing some of these questions through systematic, scientific inquiry. We review the available published evidence on the implementation of DSD and suggest further health systems innovations needed to maximize the public health impact of DSD and future implementation science research directions in this expanding field.

RECENT FINDINGS

While early observational data supported the effectiveness of various DSD models, more recently published trials as well as evaluations of national scale-up provide more rigorous evidence for effectiveness and performance at scale. Deeper understanding of the mechanism of effect of various DSD models and generalizability of studies to other countries or contexts remains somewhat limited. Relative implementability of DSD models may differ based on patient preference, logistical complexity of model adoption and maintenance, human resource and pharmacy supply chain needs, and comparative cost-effectiveness. However, few studies to date have evaluated comparative implementation or cost-effectiveness from a health systems perspective. While DSD represents an exciting and promising "next step" in HIV health care delivery, this innovation comes with its own set of implementation challenges. Evidence on the effectiveness of DSD generally supports the use of most DSD models, although it is still unclear which models are most relevant in diverse settings and populations and which are the most cost-effective. Challenges during scale-up highlight the need for accurate differentiation of patients, sustainable inclusion of a new cadre of health care worker (the community health care worker), and substantial strengthening of existing pharmacy supply chains. To maximize the public health impact of DSD, systems need to be patient-centered and adaptive, as well as employ robust quality improvement processes.