ESR undertakes STI surveillance on behalf of the Public Health Agency. The purposes on New Zealand STI surveillance system are:
- to understand the burden of disease (as an input to planning, policy development, prioritisation and resource allocation),
- to monitor inequalities in the burden of disease between population groups,
- to monitor trends in the burden of disease over time,
- to identify emerging problems, and outbreaks or clusters of disease, and
- to evaluate the effectiveness of policies and programmes.
Before the Health (Protection) Amendment Act 2016 came into force, STI surveillance comprised a combination of voluntary sentinel clinic surveillance from Sexual Health and Family Planning Clinics, enhanced syphilis surveillance from these clinics, and laboratory surveillance of chlamydia and gonorrhoea.
Significant changes were made to the STI surveillance system after the Health (Protection) Amendment Act 2016 came into force in January 2017, making syphilis, gonorrhoea, HIV and AIDS notifiable to the Medical Officer of Health without identifying information (name, address and place of work), whereas previously only AIDS was notifiable. An interim solution was put in place from November 2018 using REDCap, a secure web application hosted on an ESR server, to collect data for syphilis, gonorrhoea and HIV in a survey format. For further information on the surveillance system please see Appendix 2 description of STI surveillance system and methodology in the 2021 supplementary report.
Analytical methods for quarterly dashboard:
Quarterly dashboard updates are based on data submitted at least two weeks before dashboard publication. Any data submitted after this point will be reflected in subsequent quarterly updates to the dashboard.
Calculations for ethnicity use the Ministry of Health prioritised ethnicity definition.
For laboratory based surveillance rates, the numerator is the total number of laboratory-confirmed cases reported after exclusion of repeat tests for an individual within a defined episode period for the specific disease.
For infectious syphilis surveillance, the case counts are those cases classified as confirmed or probable based on the surveillance case definition.
Where there is insufficient information provided, ethnicity is reported as Unknown.
Caveats for interpreting rates:
- Rates will not be presented where there were fewer than five cases in any category due to instability in these rates.
- We advise dashboard viewers to consider the absolute number of cases that make up the numerator (see case counts) of any rate being interpreted.
- With few cases in a numerator, rates could change dramatically based on differences of 1-2 cases. Rates with fewer than 20 cases in the numerator should be interpreted and compared to other rates with caution.
- Sometimes, the highest rates involve few cases and therefore a relatively small proportion of the overall disease burden for New Zealand.
Laboratory-based surveillance rates use the applicable mid-year population estimates published by Statistics New Zealand as the denominators. Population estimates are downloaded from the Statistics New Zealand website annually and include estimates stratified by age, sex, and ethnicity (prioritised based on Ministry of Health definitions).