The Aotearoa New Zealand (NZ) Sexually Transmitted and Blood Borne Infection Strategy 2023–2030 aims to reduce sexually transmitted infection (STI) incidence and improve health outcomes for inequitably affected groups, including Māori, Pacific peoples, young people and men who have sex with men (MSM).1 In the current analysis, we build on the methods and analysis strategies previously described2 to create a national-level population-based cohort of STI among people aged 15+ years; we aim to examine predictors of gonorrhoea, chlamydia or syphilis coinfections between 2018 and 2022 in NZ.

The Institute of Environmental Science and Research (ESR), a Crown Research Institute, manages, analyses and reports the data for the NZ STI surveillance system.3 Gonorrhoea and syphilis are both notifiable diseases in NZ, and chlamydia is not notifiable. ESR obtains chlamydia and gonorrhoea case data through laboratory surveillance, while syphilis case data are while syphilis case data are submitted by treating clinicians.

National Health Index numbers (NHIs), unique to each person who has received healthcare in NZ, were used to link STI cases. STIs diagnosed within 30 days of each other were considered coinfections. Testing history was available for chlamydia and gonorrhoea cases through laboratory data and matched using NHIs.

To determine the odds of having coinfection, we performed a logistic regression. The covariates considered …