Sexually Transmitted Infection Surveillance Network (SSuN) - California has the largest burden of bacterial sexually transmitted infections (STI) of any jurisdiction in the USA. In 2022, the state accounted for 12.4% and 14.4% of the national gonorrhea and early syphilis (including primary, secondary, and early non-primary non secondary infections) cases, respectively, when there were 16,723 early syphilis and 80,317 gonorrhea cases (97,040 cumulatively) reported to the California Department of Public Health (CDPH). The state’s population that yields this morbidity is comprised of nearly 40 million diverse residents including a multitude of racial/ethnic groups (including the largest American Indian population of any state), gender/sexual minorities (including lesbian, gay, bisexual, transexual, queer, intersex, asexual and others [LGBTQI+]), people of lower socio-economic status, people experiencing homelessness, and others who have experienced historical trauma and marginalization. Due to our state’s high morbidity and diverse population, CDPH is ideally situated to capture impactful surveillance data that describe the impacts of STI and can be used to identify opportunities and gaps across the STI/HIV prevention continuum. While STI surveillance in California is robust in many regards, increasing morbidity juxtaposed with dwindling resources and emergent challenges related to COVID-19 and mpox have led to gaps in our understanding of how STIs impact Californians. These have hindered our ability to 1) elicit data that enable a comprehensive understanding of STI risk patterns (including the use and effectiveness of novel biomedical interventions such as doxy PEP, MenB, and JYNNEOS vaccination), and 2) build an evidence base to inform STI control and prevention efforts. As such, we propose an expansion of our SSuN Cycle IV activities that furthers our syndemic approach to STI/HIV (incl. mpox) surveillance and response efforts and enables more flexible responses to emergent health issues. Strategy A activities will continue our partnership with the Orange County Health Care Agency (OCHCA) at the 17th Street Testing and Treatment Clinic, a medium volume STI clinic with >4000 unique patients per year. This clinic provides integrated STI/HIV services, including HIV pre- and post-exposure prophylaxis, doxy PEP, and prophylactic vaccinations. They are poised to participate in SSuN due to their participation as a Strategy A partner for Cycle IV, a robust electronic health record system (PowerChart by Cerner), a diverse patient population from a large Southern California catchment area, and a high disease burden that is representative of STI morbidity in Orange County. Our Strategy B activities expand upon infrastructure developed for Cycle IV and enhance this already robust provider and case-based surveillance. We are adapting a new surveillance tool (CalCONNECT), initially developed for COVID-19, that will enable integrated STI/HIV follow-up and include new tools for timely and thorough outreach. In conjunction with electronic case reporting (eCR) of electronic health records these two tools will enable more robust surveillance for enhanced biomedical interventions like doxy PEP, disseminated gonococcal infections, and indications of otic, ocular, and neurosyphilis, alongside other improvements upon our Cycle IV enhanced surveillance activities. Lastly, the implementation of CalCONNECT and eCR will enable a sampling range from 3 to 10%. Given the size and diversity of our population, volume of STI morbidity, partnership with the OCHCA 17th Street Testing and Treatment Clinic, the deployment of a new case investigation tool (CalCONNECT), and electronic case reporting, our proposed activities are a key contribution to the SSuN project that will serve as a model for the implementation of sentinel facility-based and enhanced case-based surveillance for STI.