Eurosurveillance - Volume 30, Issue 36, 11 September 2025

The global goal to end the AIDS epidemic cannot be achieved without estimates of incidence and undiagnosed infection.

We aimed to estimate the timing of HIV transmission events and the number of people unaware of their diagnosis in Scotland, by mode of acquisition and migrant status.

Surveillance data from Scotland’s national HIV diagnosis database (1981–2022) linked to death and migration data was entered into the HIV Platform tool of the European Centre for Disease Prevention and Control, to back-calculate HIV incidence while imputing missing data and adjusting for reporting delay.

We estimated 8,235 HIV transmission events between 1980 and 2022 among people living in Scotland, with an 80% reduction from 2010 to 2021 (258 to 52 events). Excluding people diagnosed outside Scotland, we estimated 4,854 (95% confidence interval (CI): 4,637–5,080) people living with HIV at the end of 2021, of whom 8.2% (396/4,854) were undiagnosed. Stratified estimates of this proportion were 6.9% for gay, bisexual and other men who have sex with men, 7.0% for people who inject drugs, 12.6% and 12.4% for heterosexuals born and not-born in the United Kingdom (UK), respectively. Including people first diagnosed with HIV outside Scotland, the overall proportion undiagnosed was 6.1% (396/6,444).

Scotland is on track to meet the United Nations' diagnosis target of 95% by 2025, with the World Health Organization target of a 75% incidence reduction met since 2010. To reduce further transmission, expanded HIV testing and prevention services are necessary to better reach at-risk heterosexual individuals.

Lyme borreliosis (LB) caused by Borrelia burgdorferi sensu lato (Bbsl) spirochetes is the most common tick-borne infection in Europe and the incidence of LB has been increasing in many countries.

We examined changes in Bbsl seroprevalence in Finland over the past 50 years.

We analysed samples collected from people aged ≥ 15 years in nationwide cross-sectional health surveys conducted over the years 1966–1972, 1978–1980, 2000–2001 and 2017. Samples were screened with an IgG ELISA assay and confirmed with an IgG bead immunoassay. We assessed factors associated with Bbsl seropositivity by generalised linear models.

Seroprevalence was highest in 1966–1972 (25.0%; 95% confidence interval (CI): 22.3–27.7%), while it was lower in 1978–1980 (16.6%; 95% CI: 14.3–18.9%), 2000–2001 (7.4%; 95% CI: 5.8–9.0%) and 2017 (3.4%; 95% CI: 2.3–4.5%). Male sex (p = 0.0014) and increasing age (p < 0.0001) were associated with higher seropositivity. The estimated probability of being seropositive was highest among residents from southern (least squares (LS) mean: 0.164; 95% CI: 0.139–0.192), central and eastern Finland (LS mean: 0.141; 95% CI: 0.116–0.170) and lowest in northern Finland (LS mean: 0.019; 95% CI: 0.014–0.028).

Our results show a decrease in the seroprevalence in Finnish people over time. Reasons for this decrease are not clear but could be related to urbanisation, increased awareness, effective diagnostics and prompt antibiotic treatments. Overall, this study demonstrates how repeated serosurveys can help in revealing trends and identifying potential risk groups.