Methods: Notifications to NSW Health of chlamydia and gonorrhoea between 2000 and 2012 were deterministically matched by given name, surname and date of birth, to create a de-identified person based record. 107,553 persons were grouped by number of infections recorded. Re-infections were defined as new notifications, 30 days to 13 months after the initial notification. Logistic regression was used to determine demographic differences between individuals with single notifications compared to those with re-infections within 13 months by area of residence, age group, sex and year of first notification.
Results: 94,930 individuals had an initial chlamydia notification of which 4,730 (5.0%) individuals had a re-infection. 11,263 individuals had an initial gonorrhoea notification of which 717 (6.4%) individuals had a re-infection. 1,367 individuals had an initial co-infection of chlamydia and gonorrhoea of which 150 (11.0%) had a re-infection. Young people, particularly residents outside metropolitan Sydney, were more likely to have a re-infection following an initial chlamydia infection. Females were more likely to be re-infected within 13 months of a chlamydia infection than males. Notifications for both STIs increased over time, however re- infections only increased for chlamydia. The proportion of re-infections following a gonorrhoea infection were stable over time.
Conclusion: This study found that young people particularly residents outside metropolitan Sydney were more likely to have a re-infection following an initial chlamydia infection. The high number of notifications and re-infections for young people indicates ongoing risk behaviours.