Title: Age related factors influence HIV testing within subpopulations: a cross sectional survey of MSM within the Celtic nations

Objectives Despite a recent fall in the incidence of HIV within the UK, men who have sex with men (MSM) continue to be disproportionately affected. As biomedical prevention technologies, including preexposure prophylaxis (PrEP) are increasingly taken up to reduce transmission, the role of HIV testing has become central to management of risk. Against a background of lower testing rates among older MSM, this study aimed to identify age related factors influencing recent (≤ 12 months) HIV testing. Methods Cross sectional sub-population data from an online survey of sexually active MSM in the Celtic nations: Scotland, Wales, Northern Ireland and the Republic of Ireland (n=2436) were analysed to compare demographic, behavioural and socio-cultural factors influencing HIV testing between MSM aged 16-25 (n=447), 26-45 (n=1092) and ≥46 (n=897). Results Multivariate logistic regression demonstrated that for men aged ≥ 46, not identifying as gay (OR 0.62 CI 0.41-0.95), location (Wales) (OR 0.49, CI 0.32-0.76) and scoring higher on the personalised stigma scale (OR 0.97, CI 0.94-1.00) significantly reduced the odds for HIV testing in the preceding year. Men aged 26-45 who did not identify as gay (OR 0.61, CI 0.41-0.92) were also significantly less likely to have recently tested for HIV. For men aged 16-25, not having a degree (OR 0.48, CI 0.29-0.79), location (Republic of Ireland) (OR 0.55, CI 0.30-1.00) and scoring higher on emotional competence (OR 0.57, CI 0.42-0.77) were also significantly associated with not having recently tested for HIV. Conclusion Key differences in age related factors influencing HIV testing suggest health improvement interventions should accommodate the wide diversities among MSM populations across the life course. Future research should seek to identify barriers and enablers to HIV testing among the oldest and youngest MSM, with specific focus on education and stigma. BACKGROUND Since 2016, the incidence of HIV has fallen among all subpopulations within the UK and remained steady within the Republic of Ireland. [1,2] In 2017, however, 53% of all new diagnoses in both nations occurred among men who have sex with men (MSM) clearly evidencing that this group remains disproportionately affected. [3] HIV testing is recognised as a key pillar of HIV risk reduction, in order to identify people who have acquired HIV and to facilitate early access to treatment, enabling the success of biomedical interventions including treatment as prevention (TasP). For HIV negative people at high risk of infection, testing is a baseline for consideration of HIV pre-exposure prophylaxis (PrEP). [4] This is of particular concern in the UK where, in England an estimated 4200 MSM remain undiagnosed, and in Scotland, over one third of MSM with HIV are undiagnosed. [1,5] Late diagnosis of HIV, characterised as having a CD4 cell count of less than 350, is associated with unfavourable outcomes, including a significantly higher likelihood of death within one year. [6] Over 30% of the most recently reported HIV diagnoses among MSM in the UK and the Republic of Ireland were late, representing the greatest number of late diagnoses among the subpopulation groups. [2,3] In Northern Ireland, despite a substantial recent rise in first episode testing of MSM in sexual health clinics, almost 30% of HIV diagnoses among this group were categorised as late. [7] The British Association for Sexual Health and HIV (BASHH) guidelines recommend annual testing for all sexually active MSM. [8] This advice is supported by recent evidence from sexual health services in England where 77% of MSM diagnosed with HIV had not been tested within two years, compared with 8% who had had at least two tests in the preceding year. [2]. Testing among older MSM in the UK, however, remains problematic, with the over 40s among those least likely to have recently tested for HIV. [9-11] While MSM aged between 25 and 45 are most likely to acquire HIV in the UK, recent evidence demonstrates that MSM in middle age and beyond remain sexually active and at risk of HIV acquisition. [2,12] In England, the same percentage of MSM aged 5064 were diagnosed with HIV in 2017 as those aged 36-49. [2] In addition, European trends point to a steeper rise of HIV diagnoses among MSM aged over 50 than younger men, further reinforcing that this age group warrants attention. [13] Existing evidence associates socio-demographic, as well as complex socio-cultural and behavioural factors with HIV testing frequency among MSM, including environment, education, risk related activity, gay identity, cultural norms and stigma. [9,11,13-16,] It remains unclear, however, whether factors influencing HIV testing vary across the life course. Such an understanding would facilitate targeted health improvement interventions, avoiding homogenising several generations of MSM. This is of particular concern to the current cohort of ageing MSM, whose older men have lived through dramatic sociocultural changes, including the introduction of sexual rights legislation and the devastating impact of HIV. [17] It is unclear to what extent living through these earlier experiences when young governs current testing behaviour. This study therefore aims to identify age related factors influencing recent HIV testing within a sample of MSM, incorporating men from Scotland, Wales, Northern Ireland and the Republic of Ireland. These countries are known collectively as Celtic nations for political, ethno-cultural and language related reasons, and are referred to as such within this paper for ease of identification. [18]