Unpacking Chlamydia in Victoria: Retrospective analysis of surveillance data to estimate reinfection
Chlamydia is prevalent among young Australians. The latest national surveillance report (2011) shows a rate of diagnosis of 1400 per 100,000 population aged 15-29 years. In Victoria, the number of notifications in 2011 was 19,238; 81% in 15-29 year olds; however notifications continue to rise in all age groups. International evidence suggests chlamydia reinfection is responsible for a substantial burden of infections. Given the associated health risks, monitoring reinfection in the population is important to understand disease burden and evaluate interventions. We describe the rate of reinfection and time between infections in Victoria, 2004-2011.
Methods: Chlamydia notification data from the Victorian notifications database, 2004-2011 were used to conduct a retrospective cohort study. Individuals’ records were linked over time to identify reinfection. Notifications within six weeks were excluded. Two age groups were created for comparison, 15-29 years and >29 years. Two periods (P1: 2004-2007), (P2: 2008-2011) were used to identify change over time.
Results: There were 97,838 notifications of chlamydia in individuals aged >15 years in Victoria; 58% among women, 79% among individuals aged 15-29 years. Reinfections accounted for 15% (n=14,084) of total notifications, of which 11% were diagnosed within six months of a previous positive (n=1567). Time between positive diagnoses remained stable over time; median 2.4 years. The proportion of reinfections did not differ by sex or age group but increased significantly between time periods; 5.5% in P1 to 9% in P2 (p=.0001).
Conclusion: We found reinfections are contributing to increasing notifications of chlamydia in Victoria. Current guidelines recommend repeat testing three months after a positive chlamydia diagnosis which could be impacting detection of these infections. The proportion of notifications that are reinfections has increased suggesting improvements are warranted in monitoring treatment failure, sexual behaviour counseling post-diagnosis, partner testing and treatment, and follow-up to encourage repeat testing.
