{
  "abstract": "Background Addiction Services (SERD) represent a strategic setting for hepatitis C (HCV) screening and early case identification. Screening campaigns performed in 2023 and 2025 provide an opportunity to evaluate changes in the target population, screening performance, and the potential for identifying undiagnosed infections. This study compares the two campaigns to assess how population dynamics and screening coverage influence the detection of new HCV cases.Materials and Methods We retrospectively analysed aggregated data from three SERDs in Northern Sardinia. In 2023, anti-HCV screening was universally offered to all patients in care. In 2025, screening targeted only individuals who had been HCV-negative or not previously screened in 2023. Key indicators included overall population size, proportion of patients on opioid substitution therapy, screening coverage, and positivity rates among those tested.Results The SERD population increased from 1107 individuals in 2023 to 1474 in 2025 (+32.8%). The proportion of patients receiving opioid substitution therapy (OST) rose from 55.9% (619/1107) to 61.4% (905/1474), corresponding to a 9.8% relative increase and indicating a progressively more complex case-mix ( figure 1).Screening performance differed between the two campaigns. In 2023, 849 of 1107 patients were screened (coverage 76.7%). In 2025, among 378 individuals eligible for screening, 248 were tested (coverage 65.6%) (figure 2), suggesting that the growing and more heterogeneous population was increasingly difficult to reach. Despite this, anti-HCV positivity among newly screened individuals in 2025 remained high: 106 of 248 subjects (42.7%). This confirms the presence of a substantial reservoir of previously undiagnosed infection.The apparent reduction in seroprevalence observed between the two campaigns - from approximately 80% in 2023 to 42.8% in 2025 (figures 3, 4) - does not reflect a true epidemiological improvement. Rather, it results from the substantial expansion of the SERD population, which now includes a large proportion of individuals whose HCV status is either negative or simply unknown due to lack of testing. As a consequence, the relative weight of known anti-HCV-positive patients decreases within a much larger denominator, leading to an artefactual decline in calculated seroprevalence. The underlying burden of HCV infection within the SERD population therefore remains significant, as demonstrated by the high positivity rate (42.7%) among newly screened individuals in 2025.Conclusions Comparison of the 2023 and 2025 screening campaigns highlights major changes in population size and complexity within SERDs, accompanied by a reduction in screening coverage. The persistently high proportion of positive tests among newly screened individuals in 2025 demonstrates the ongoing presence of hidden HCV infection. These findings reinforce the importance of repeated, structured screening initiatives to ensure the emergence of undiagnosed cases and to support HCV elimination efforts within addiction care settings.Abstract OC9 Figure 1–4",
  "authors": [
    {
      "affiliations": [
        "Unit of Infectious Diseases, Department of Medicine, Surgery and Pharmacy, University of Sassari, Sassari, Italy"
      ],
      "name": "A Bilotta"
    },
    {
      "affiliations": [
        "Unit of Infectious Diseases, Department of Medicine, Surgery and Pharmacy, University of Sassari, Sassari, Italy"
      ],
      "name": "E Princic"
    },
    {
      "affiliations": [
        "Unit of Infectious Diseases, Department of Medicine, Surgery and Pharmacy, University of Sassari, Sassari, Italy"
      ],
      "name": "S Babudieri"
    },
    {
      "affiliations": [
        "Unit of Infectious Diseases, Department of Medicine, Surgery and Pharmacy, University of Sassari, Sassari, Italy"
      ],
      "name": "G Madeddu"
    },
    {
      "affiliations": [
        "Azienda Sanitaria Locale (ASL) di Sassari, Sassari, Italy"
      ],
      "name": "G Seu"
    },
    {
      "affiliations": [
        "Azienda Sanitaria Locale (ASL) di Sassari, Sassari, Italy"
      ],
      "name": "P Milia"
    },
    {
      "affiliations": [
        "Unit of Infectious Diseases, Department of Medicine, Surgery and Pharmacy, University of Sassari, Sassari, Italy"
      ],
      "name": "I Maida"
    }
  ],
  "title": "OC9 High diagnostic yield of repeated HCV screening in addiction services: compared findings from two large-scale campaigns in 2023 and 2025",
  "uid": "36770d55-c4a6-520d-a0dd-2714856c238e"
}