What can be gained from comprehensive disaggregate surveillance? The Avon Surveillance System for Sexually Transmitted Infections

OBJECTIVE: To describe a new disaggregate surveillance system covering key diagnosed sexually transmitted infections in a UK locality. METHODS: The Avon System for Surveillance of Sexually Transmitted Infections (ASSIST) collects computerised person- and episode-based information about laboratory-diagnosed sexually transmitted infections from genitourinary medicine clinics, the Avon Brook Clinic, and Health Protection Agency and trust laboratories in primary care trusts in Avon. We illustrate features of the system by describing chlamydia testing patterns according to source of test, age and sex, and mapped the distribution of chlamydia across Bristol. RESULTS: Between 2000-2004 there were 821,685 records of tests for sexually transmitted infections and 23,542 positive results. The proportion of tests and positive results for chlamydia and gonorrhoea sent from general practice increased over time. Most chlamydia tests in both genitourinary medicine and non-specialist settings were from women over 25 years, but positivity rates were highest in under 25 year olds. The positivity rate remained stable between 2000 and 2004. Including data from all diagnostic settings, chlamydia rates were about twice as high as those estimated only from genitourinary clinic cases. CONCLUSIONS: The ASSIST model could be a promising new tool for planning and measuring sexual health services in England if it can become sustainable and provide more timely data using fewer resources. Collecting denominator data and including infections diagnosed in primary care are essential for meaningful surveillance.