Project Summary / Abstract HIV remains a major public health concern in the United States. The proportions of people with HIV (PWH) in 2020 who knew their HIV status, were linked to care, retained in clinical care (50%), and had suppressed viral loads (57%), were lackluster. Retention in clinical care is a core quality-of-care indicator and the central stage of the HIV care continuum. Suboptimal clinical retention is strongly associated with virologic failure while on ART, high-risk behavior, and poorer survival. Furthermore, it is estimated that 43% of new HIV transmissions are from PWH who are out of care (the largest proportion from any one care continuum stage). The implication, echoed in multiple public health policies over the past decade, is that high retention and engagement in clinical care are critical for blunting the HIV-related morbidity and mortality and reducing the number of new HIV infections. However, despite consensus that “retention” in care is critical and “engagement” in care must be increased, we do not fully understand how best to measure retention and engagement among patients in high-income settings, particularly in the modern ART era and given changes in care delivery that were introduced during the COVID-19 pandemic. Earlier research indicated that sicker patients (i.e., those with lower CD4) were more likely to miss clinic visits. More recent work, though, found that patients attending clinic visits less frequently may continue to receive laboratory monitoring services; this could well be an indication that healthier patients (i.e., those with higher CD4) who are stably virally suppressed are compliant with newer monitoring guidelines which demand less frequent clinic visits. However, the field has yet to delineate the optimal frequency of clinic visits for these healthier, virally suppressed patients as opposed to individuals in multiple other risk strata, though applying a single metric regardless of sub-population could produce spurious findings of poor retention among clinically stable individuals. In this respect, our proposal is truly novel. The proposed research will therefore extract, harmonize, and analyze readily available data on clinical care patterns within the largest HIV cohort in North America: the North American AIDS Cohort Collaboration on Research and Design. We will use these data to describe patterns of retention and engagement (Aim 1), isolate multiple measures of care receipt (Aims 1 and 2) that predict improved survival and viral suppression, and assess multiple methods for stratifying populations while quantifying the expected causal impact of improved retention on HIV outcomes under existing and novel, optimized metrics (Aim 3). The public health impact of improved retention metrics, based on population-specific HIV clinical care engagement, would be profound, particularly in light of changes in HIV disease and comorbidity clinical management and laboratory monitoring under a primary care ...