Chlamydia trachomatis in Tasmania : improving public health surveillance methods to reduce the burden of disease

Background: Genital Chlamydia trachomatis (chlamydia) is Australia's most frequently notified communicable disease. Associated costs have been estimated at between AUD$90-$160 million per year. Chlamydia infection can lead to significant health complications including infertility in both sexes. Public health surveillance data based on statutory notifications of cases provides epidemiological information useful in focussing chlamydia control efforts, however the data is limited without knowledge of testing patterns. Clinical guidelines recommend annual tests for all sexually active people aged <30 years, and mathematical modelling demonstrates that large reductions in chlamydia prevalence are possible, provided there is adequate testing coverage. Aims: To investigate, in Tasmania: i) increasing rates of chlamydia notifications by demographic and risk profiles and behavioural characteristics; ii) rates of testing, retesting and test positivity; iii) the feasibility and usefulness of collecting population-level testing data; iv) potential clinical and behavioural influences on test positivity trends; v) whether testing effort is reaching strategic and clinical guidelines; vi) the role and type of healthcare provider in chlamydia testing. Methods: Four Tasmanian datasets were analysed i) statutory data on all chlamydia cases notified from 2001-2010; ii) additional surveillance data collected on all notified cases of chlamydia from 2001-2010; iii) de-identified laboratory testing data collected from 2001-2010; and iv) linked laboratory testing data collected in 2012 and 2013. Data were analysed by sex, geographic location, indigenous status, sexual exposure, reason for testing and healthcare provider. Testing patterns and positivity levels were examined and compared with data collected on notified cases. Population rates of testing and retesting, and test positivity were measured by sex, healthcare provider, geographic location and socioeconomic indicators. Results: Females were more likely to have been tested as a result of screening, males as a result of presenting with symptoms or from contact tracing. General practitioners identify the majority of cases. Testing and retesting rates are lower than recommended levels. Testing and test positivity increased from 2001 to 2010, most significantly in males and females aged 15-24 years; testing coverage was higher in females (21%) than males (6%) and test positivity was higher in males (16%) than females (10%). In 2012 and 2013, less testing and higher test positivity was found in areas of most disadvantage; retest rates at 3 months were low in males (10%) and females (14%), and retest positivity high in males (35%) and females (23%). Conclusions: Chlamydia infection is a significant public health issue. After allowing for testing effort, an increase in notifications in young people was found in Tasmania. Testing levels are below those required to decrease chlamydia prevalence. Analysis of chlamydia testing, retesting and positivity trends can inform the development, monitoring and evaluation of prevention and control activities and improves the interpretation of notification data.