Population-level diagnosis and care cascade for chlamydia in Australia

Objectives: Key strategies to control chlamydia include testing, treatment, partner management and re-testing. We developed a diagnosis and care cascade for chlamydia to highlight gaps in control strategies nationally and to inform efforts to optimise control programmes. Methods: The Australian Chlamydia Cascade was organised into four steps: (1) annual number of new chlamydia infections (including re-infections); (2) annual number of chlamydia diagnoses; (3) annual number of diagnoses treated; (4) annual number of diagnoses followed by a re-test for chlamydia within 42-180 days of diagnosis. For 2016, we estimated the number of infections among young men and women aged 15-29 years in each of these steps using a combination of mathematical modelling, national notification data, sentinel surveillance data and previous research studies. Results: Among young people in Australia, there were an estimated 248 580 (range, 240 690-256 470) new chlamydia infections in 2016 (96 470 in women; 152 100 in men) of which 70 164 were diagnosed (28.2% overall: women 43.4%, men 18.6%). Of the chlamydia infections diagnosed, 65 490 (range, 59 640-70 160) were treated (93.3% across all populations), but only 11 330 (range, 7660-16 285) diagnoses were followed by a re-test within 42-180 days (17.3% overall: women 20.6%, men 12.5%) of diagnosis. Conclusions: The greatest gaps in the Australian Chlamydia Cascade for young people were in the diagnosis and re-testing steps, with 72% of infections undiagnosed and 83% of those diagnosed not re-tested: both were especially low among men. Treatment rates were also lower than recommended by guidelines. Our cascade highlights the need for enhanced strategies to improve treatment and re-testing coverage such as short message service reminders, point-of-care and postal test kits.