BACKGROUND AND AIMS: People who inject drugs (PWID) have a substantial risk of acquiring human immunodeficiency virus (HIV) infection. From 1999-2000 in Ireland, there were 115 new HIV cases among PWID, 40% in individuals aged under 22 years. However, over the past two decades, HIV incidence has declined among PWID in Western Europe, including Ireland. We investigated secular changes in HIV incidence among PWID in Ireland. Also, new HIV cases in two time periods 2000-2009 and 2010-2018 were compared by sex, age group, area of residence and country of birth.

DESIGN: Longitudinal observational study in the Republic of Ireland, 2000-2018. A total of 753 new cases of HIV in PWID were diagnosed. Diagnosis rates of HIV in PWID were calculated and changes in rates over the period were modeled.

FINDINGS: Over the period 2000-2018, HIV incidence among 15-29 year-old PWID in Ireland declined from 5.69 to 0.11 cases per 100,000, equivalent to a yearly decline of 0.22 cases per 100,000. Among PWID aged 30-64 years, HIV incidence declined annually by 0.06 cases per 100,000 from 1.80 to 0.57 cases per 100,000. Comparing 2000-2009 to 2010-2018, there was a relative increase in HIV cases among older adults (p<0.001), and those born outside Ireland accounted for a growing minority of cases. Changes by sex (p=0.10) and area residence (p=0.39) were not statistically significant.

CONCLUSION: Since 2000, Ireland has achieved an ongoing reduction in the incidence of human immunodeficiency virus among people who inject drugs and this is most evident among young adults. The reduction has occurred in the context of a reasonably comprehensive, health-led and harm reduction orientated national drugs strategy.