Overseas- and locally-acquired sexually transmissible infections in Australia, 2017-2023.

Introduction: International travel is a significant contributor to the acquisition of sexually transmissible infections (STIs). Despite the high volume of outbound travel from Australia, peaking at 10.8 million travellers in 2023, limited data exist on the burden of overseas-acquired STIs. This study aims to investigate the burden and trends of overseas- and locally-acquired STIs in Australia.

Methods: We analysed STI cases notified to Australia's National Notifiable Diseases Surveillance System (NNDSS) from January 2017 to December 2023. A comparative analysis was conducted by place of acquisition (i.e., overseas versus local), with the geographical origins of overseas-acquired cases mapped using ArcMap and temporal trends assessed across pre-COVID-19, pandemic, and post-pandemic periods.

Results: A total of 967,193 records were obtained from NNDSS, of which 188,788 STI cases (11,782 overseas- and 177,006 locally-acquired) were included in the analysis. Males were the most affected group (63% of overseas- and 60% of locally-acquired), and young adults aged 20-24 year represented a quarter of cases (24.6% of overseas- and 25.9% of locally-acquired). The incidence of overseas-acquired STIs cases rose nearly 3-fold, from 12.8 per 100,000 travellers in 2017 to 35.0 per 100,00 travellers in 2019, then declined during the COVID-19 pandemic due to Australia's travel restrictions to 16.4 per 100,000 travellers in 2020. A surge was observed in 2021, with 46.5 per 100,000 travellers. The most common regions of acquisition were Southeast Asia (n=2,390, 44.6%), North and South America (n=663, 12.4%), and Northwest Europe (n=580, 10.8%).

Conclusions: This study highlights the patterns of overseas- and locally-acquired STIs in Austrlia, with chlamydia remaining the most prevalent (but declining since 2021), while gonorrhoea has been increasing, among overseas-acquired cases. Variations in region of acqusition and demogrpahic factors highlight the critical need for tailored safer-sex advice during pre-travel consultations, particularly for males and young adults travelling to high-prevalence destinations.