National trends in rates of undiagnosed HIV in key populations in Australia: a retrospective observational analysis from 2008 to 2019

Introduction Determining the proportion of people living with HIV who are undiagnosed is critical for Australia to accurately assess the country’s progress toward UNAIDS’ 95-95-95 interim targets by 2025 and progress with elimination goals. We aimed to investigate the utility of two additional measures, the Yearly Diagnosed Fraction, and the Case Detection Rate, in elucidating trends over time in the rate of undiagnosed HIV. Methods Using routinely collected national HIV surveillance data, we produced estimates for the number living with undiagnosed HIV and the number of new HIV infections using the European Centre for Disease Protection and Control (ECDC) HIV modelling tool to calculate the Total Diagnosed Fraction (TDF), the Yearly Diagnosed Fraction (YDF), and the Case Detection Rate (CDR) from 2008 to 2019 for Australian-born and overseas-born individuals who have reported having male-to-male sexual contact, and heterosexual women and men. We calculated rate ratios using Poisson Regression models to compare trends for each sub-population. Results Over 2008-2019, each metric for the Australian-born male-to-male sexual contact group improved consistently over the period with the case detection rate rising above one in 2013. The total diagnosed fraction for the overseas born group fell slightly from 85.0% to 81.9%, the yearly diagnosed fraction fell from 23.1% to 17.8% and the case detection rate stayed below one, falling from 0.74 to 0.63. In the heterosexual group, women and men had consistent increasing trends for the total diagnosed fraction and yearly diagnosed fraction but with women having consistently higher estimates than men, 92.6% vs 80.8% and 26.3% vs 17.4%, respectively in 2019. However, heterosexual men had a declining case detection rate, falling below one in 2019 (0.83), compared to an increase for women. Conclusion The additional metrics presented provide important information on Australia’s progress toward HIV elimination. The more dynamic changes in the undiagnosed population seen highlight diverging trends for key populations with growing undiagnosed populations not seen in the total diagnosed fraction. Periodic trend analyses will help strengthen the use of the metrics and ease of interpretation for national surveillance reporting. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The Kirby Institute is funded by the Australian Government Department of Health, and is affiliated with the Faculty of Medicine, UNSW Sydney, Australia. The content of this publication is solely the responsibility of the authors. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: No IRB oversight was needed for this study. Modelling estimates were generated using data obtained through routine surveillance mechanisms. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The code used to produce the estimates with aggregate data and results for this study are available online at https://zenodo.org/record/7058987. Updated code available from https://github.com/The-Kirby-Institute/Cascade_calculations. . * CDR : Case detection rate TDF : Total diagnosed fraction YDF : Yearly diagnosed fraction