Demographic and geographical risk factors for gonorrhoea and chlamydia in greater Western Sydney, 2003-2013.

Introduction: Notification rates of sexually transmitted infections (STIs) have increased in New South Wales as elsewhere in Australia. Understanding trends in chlamydia and gonorrhoea notifications at smaller geographical areas may assist public health efforts to deliver targeted STI interventions.

Methods: Routinely collected disease notification data from 2 local health districts within the greater Western Sydney area were analysed. De-identified notifications of gonorrhoea and chlamydia were extracted for people aged over 15 years during the period 1 January 2003 to 31 December 2013. Sex-specific and age-specific population notification rates for each infection were calculated. Incidence rate ratios were also calculated with age group, sex, year and local government area (LGA) of residence as explanatory variables.

Results: Rates of gonorrhoea and chlamydia increased among males and females over the period. Males had a 4-fold increased risk of gonorrhoea (P<0.0001). Compared with the 30-44 years age group, young people aged 15-29 years had a 70% increased risk of gonorrhoea and a 4-fold increased risk of chlamydia (P values < 0.0001). Chlamydia notifications demonstrated smaller and more uniform annual increases across LGAs compared with gonorrhoea notifications, which appeared more highly clustered.

Conclusion: Analysis of notification rates of chlamydia and gonorrhoea in the greater Western Sydney area suggest that young people aged 15-29 years and residents of particular LGAs are at greater risk of infection. A limitation was the unknown effect of patterns of testing. Nevertheless, these results can support the planning of local sexual health clinical services as well as the design of targeted health promotion interventions.