Abstract Background Geographic variation in advanced therapy use for inflammatory bowel disease (IBD) has been reported across Europe (1) and North America (2), where higher latitudes consistently show greater prescribing and disease prevalence. However, comparable evidence from the Southern Hemisphere is lacking. Australia’s wide north-south span and universal health system provide a unique setting to examine whether such gradients persist within a single country. Methods Nationwide Pharmaceutical Benefits Scheme data (2007-2025) on advanced therapies, capturing 100% of subsidied prescriptions nationwide, were analysed by state and territory. Prescriptions were standardised per 1,000 IBD patients. Regression analyses were done to examine associations with latitude, ultraviolet (UV) index, and temperature, among other environmental, demographic, healthcare access, and health and lifestyle modifiers. Results More than 2.2 million prescriptions were supplied during the 18-year study period, with rapid growth after 2015 driven by newer agents. Disparities among states and territories were observed, with prescription numbers lowest in the Northern Territory (404/1,000 IBD patients) and highest in Tasmania (1,004/1,000) (Figure 1). Prescription use increased with latitude, where every 10o further south corresponded to an increase in fold-difference of ∼0.5 (95% CI 0.35-0.68, p = 0.0004). This translates to nearly 2.5-fold higher rates in Tasmania (∼43 oS) compared with the NT (∼15 oS). Latitude accounted for most of the variation in prescribing between states (R2=0.89). Prescription numbers were also inversely related to mean temperature (R2=0.92) and peak UV index (R2=0.86). Other demographic, healthcare, and lifestyle modifiers were non-significant (Figure 2). Conclusion For the first time in any Southern Hemisphere country, this nationwide analysis demonstrates a clear north-south gradient in advanced IBD therapy prescribing. These findings suggest an environmental signal linked to latitude, UV exposure and ambient temperature. Although traditionally attributed to vitamin D synthesis, the persistence of this gradient despite negative vitamin D intervention trials implies alternative UV-mediated mechanisms, such as effects on mucosal immunity, microbial composition or systemic immune regulation. These findings provide novel evidence of a latitude-dependent gradient within a single national health system and highlight potential environmental determinants of IBD care in Australia. References: 1.Shivananda S, Lennard-Jones J, Logan R, Fear N, Price A, Carpenter L, Van Blankenstein M. Incidence of inflammatory bowel disease across Europe: is there a difference between north and south? Results of the European Collaborative Study on Inflammatory Bowel Disease (EC-IBD). Gut. 1996 Nov 1;39(5):690-7. 2.Khalili H, Huang ES, Ananthakrishnan AN, Higuchi L, Richter JM, Fuchs CS, Chan AT. Geographical variation and incidence of inflammatory bowel disease among US women. Gut. 2012 Dec 1;61(12):1686-92. Conflict of interest: Pajes, A Nico Nahar: I have no conflicts of interest to disclose. Pudipeddi, Aviv: Aviv Pudipeddi has received speaker honoraria or advisory board fees from AbbVie, Dr Falk Pharma, Ferring, Johnson & Johnson, Pfizer and Takeda. Paramsothy, Sudarshan: SP has served as a consultant for Vedanta Biosciences and has received speaker / advisory board fees from AbbVie, Dr Falk Pharma, Ferring, Janssen and Takeda. Kariyawasam, Viraj: Educational grants or research support – Ferring, Janssen, AbbVie, Takeda, Shire, WSLHD Research and Education network, Crohn’s and Colitis USA Speaker fees – Janssen, AbbVie, Ferring, Takeda, Pfizer, Shire, Chiesi, Celltrion, GSK, Eli-Lilly, Research Review, Limbic Advisory boards – Janssen, Takeda, Ferring, AbbVie Board director- IBD Sydney organisation (not for profit) Leong, Rupert: advisory board: AbbVie, Aspen, BMS, Celgene, Celltrion, Chiesi, Ferring, Glutagen, Hospira, Janssen, Lilly, MSD, Novartis, Pfizer, Prometheus Biosciences, Takeda, Spyre, Roche research grants: Joanna Tiddy USYD, McCusker Charitable Foundation, Celltrion, Shire, Janssen, Takeda, Gastroenterological Society of Australia, NHMRC, Gutsy Group, Pfizer
Pajes et al. (Thu,) studied this question.