LINK-B: study protocol of a retrospective and prospective project for identification and linkage to care of people living with hepatitis B in a large health area of Barcelona.

Introduction: An estimated 290 million people are living with hepatitis B virus (HBV) worldwide; in Spain, the prevalence of hepatitis B virus surface antigen (HBsAg) is 0.4%. In our setting, many HBsAg-positive individuals are not linked to care, which implies a barrier to receiving treatment and controlling the infection. The main objective of this project is to evaluate the performance of a programme designed to achieve appropriate linkage to specialist care of HBsAg-positive individuals, newly tested or previously tested and lost to follow-up.

Methods And Analysis: This is a retrospective and prospective study in which all HBsAg-positive cases recorded in the microbiology database will be identified. The retrospective phase will include cases detected between 2018 and 2020, and the prospective phase will run from January 2021 to June 2022. The project will be carried out in a tertiary university hospital covering the northern health area of Barcelona with a catchment population of 450 000 inhabitants and 16 affiliated primary care centres. The central laboratory detects approximately 1200 HBsAg-positive individuals every year; therefore, we expect to identify around 4000 patients over the duration of the project. The medical records of HBsAg-positive individuals will be consulted to identify and retrieve those who have not been appropriately linked to care. Candidates will be contacted to offer specialist disease assessment and follow-up. A website will be created to provide HBV-related information to primary care physicians, and a mobile phone application will be available to patients to improve the linkage circuits and ensure follow-up continuity.

Ethics And Dissemination: The Vall d'Hebrón Hospital Ethics Committee (PR(AG)201/2021) and the Spanish Agency of Medicines and Medical Devices approved this study. The findings will be disseminated through peer-reviewed publications and conference presentations. This programme could increase the number of HBsAg-positive individuals properly linked to care and achieve better HBV monitoring, which will have a positive impact on WHO's viral hepatitis elimination goals.