HIV Enhanced Access Testing in Emergency Department program using a Systems Analysis and Improvement Approach (HEATED-SAIA) Cluster Randomized Trial - There are ~38 million people living with HIV (PLH) globally, with the majority in low-and middle-income countries (LMICs). Incident infections are concentrated in sub-Saharan Africa and focused in difficult to reach populations, who also have higher-risk profiles for HIV, making them essential target populations for HIV Testing Services (HTS). Among target populations, men, adolescents under age 15 and young adults (AYAs) aged 15-24 years, and persons from key populations (KPs) are crucial groups in need of HIV testing and treatment. In Africa, Emergency Departments (ED) provide care to persons who often do not otherwise access health services. Data from Africa show that those seeking emergency care have high burdens of HIV, and desire ED-HTS. Thus, EDs in LMICs provide a strategic opportunity to deliver evidence-based HTS to higher-risk persons. In Kenya one in five PLH are unaware of their status, and less than half of men are reached for HIV testing at appropriate frequencies, AYAs account for 42% of new infections and KPs contribute to hyper-endemic transmission. To address this, Kenya strategy calls for utilizing facilities-based care to deliver HTS for difficult to reach populations. However, while guidelines include EDs as delivery points, HTS during emergency care in Kenya is evolving and best practices are in early development. The HIV Enhanced Access Testing in Emergency Department (HEATED) program in Kenya was developed by a collaborative team to enhance delivery of HTS, through locally appropriate and pragmatic systems initiatives. HEATED program implementation significantly improved HIV testing for the overall ED population by 31%, while also significantly increasing testing for men, AYA and KP and was acceptable by stakeholders. Although pilot evaluation of the HEATED program demonstrated improved HTS, more robust understanding of implementation strategies in ED settings, impacts on linkage to HIV care, costing and maintenance data are needed to inform development of ED-HTS programming in Kenya. The current study builds upon the HEATED program by evaluating use of the Systems Analysis and Improvement Approach (SAIA) implementation strategy (HEATED-SAIA) to improve HTS in a cluster randomized trial in all Ministry of Health EDs in Kilifi, Mombasa and Kwale Counties in Kenya. The Reach, Effectiveness, Adoption, Implementation and Maintenance framework will be used in trial assessment. Building on the HEATED pilot data and leveraging SAIA, the HEATED-SAIA program has substantial potential to improve HTS delivery by strategically engaging difficult to reach populations already interfacing with emergency health systems.