This study is part of the MACROLIVER Project, which aims to develop a digital tool for patients and their caregivers to manage liver diseases. Approximately 20-25 million individuals worldwide carry HBsAg and are co-infected with HDV, though geographic variations exist. In Italy, an estimated 10,000-20,000 individuals are affected by Delta hepatitis (HD). These data are approximate, given the absence of current population studies and effective screening methods.

Although considered rare, chronic HD (CHD) is the most aggressive form of viral hepatitis, with most patients progressing rapidly to end-stage liver disease or developing hepatocellular carcinoma at a young age, often requiring liver transplantation. Screening HBsAg-positive patients for Delta co-infection is not widespread, leading to late diagnoses. Additionally, accurate quantification of viral RNA is limited to a few specialized centers.

The lack of effective antiviral therapies has led many Delta hepatitis patients to frequently switch hepatology centers in search of treatments or to miss regular medical check-ups. However, HDV management may change significantly following the recent EMA approval of a new antiviral drug, bulevirtide-an entry inhibitor administered subcutaneously daily-reimbursed in Italy since April 2023. This drug has shown promising results in Phase II and III studies, including in cirrhotic patients with severe portal hypertension.

The COVID-19 pandemic exacerbated this situation, causing reduced access to healthcare facilities and negatively impacting patients with chronic diseases. However, it also accelerated the search for effective, high-quality digital solutions for patient management.

The ePro-Diary HDV proposes to facilitate continuous communication between patients and doctors, monitor key lab values, quality of life questionnaires, and overall health status by an application for mobile phone.

The objectives are twofold: to make patients active participants in their care-enhancing retention and adherence through an "active App-based approach"-and to evaluate changes in patient quality of life with this "active" remote approach. This tool will support clinicians and patients without replacing standard clinical monitoring.

Inclusion Criteria:

• Age > 18 years
• Diagnosis of Delta infection (anti-HDV positivity)
• Signed informed consent
• Ability to adequately understand instructions for correctly using mobile device applications.

Exclusion Criteria:

• Refusal or inability to provide informed consent.

Patients with chronic HDV hepatitis attending the Hepatology Clinics of ASST Papa Giovanni XXIII who meet the inclusion criteria will be included. For enrolled patients given access to the app, retrospective data collection will also be performed from the time of Delta's hepatitis diagnosis.