Early syphilis included primary, secondary, or early latent syphilis (<2 years) as per the definition by the Australian Department of Health [21 ]. All syphilis cases were diagnosed using Treponema-specific tests (T pallidum enzyme immunoassay [EIA] or chemiluminescence immunoassay [CLIA] and T pallidum particle agglutination assay [TPPA]) and non-Treponema-specific test (the rapid plasma reagin [RPR] test). A new early infectious syphilis was defined as (1) any positive Treponema-specific test (CLIA or EIA and TPPA) and a positive RPR compared with a previous negative result within the last 2 years, or (2) positive T pallidum polymerase chain reaction (PCR) from any suspected syphilis lesion independent of the syphilis serology result, or (3) a 4-fold rise in RPR titer from a previous serology after successful treatment of syphilis infection [21 ] (Figure 1 ). The subsequent syphilis infections after a first syphilis infection diagnosed during the study period are called repeated infections, and this could occur multiple times. All syphilis cases were reviewed by 2 sexual health clinicians independently, and any discrepancies were resolved by consensus.
Chlamydia diagnoses included infections at any anatomical sites (ie, oropharynx, urethra and/or anorectum) detected by nucleic acid amplification test using Aptima Combo 2 (AC2) assay (Hologic Panther System; Hologic, San Diego, CA, USA). Gonorrhoea infections at any anatomical sites (ie, oropharynx, urethra and/or anorectum) were diagnosed using the same method as chlamydia infection (AC2 assay) from March 2015, whereas modified Thayer Martin medium for gonorrhoea culture was used to diagnosed gonorrhoea before March 2015 [22 (link)]. Individuals who were diagnosed with concurrent gonorrhoea or chlamydia at multiple anatomical sites on the same day were considered a single infection in this analysis. The HIV infections were diagnosed using DiaSorin Liaison XL Murex HIV Ab/Ag CLIA (fourth generation) assay from April 2014 and Abbott Murex HIV-1 2.0 EIA (third generation) before April 2014 and confirmed by the Western blot assay.
Chlamydia diagnoses included infections at any anatomical sites (ie, oropharynx, urethra and/or anorectum) detected by nucleic acid amplification test using Aptima Combo 2 (AC2) assay (Hologic Panther System; Hologic, San Diego, CA, USA). Gonorrhoea infections at any anatomical sites (ie, oropharynx, urethra and/or anorectum) were diagnosed using the same method as chlamydia infection (AC2 assay) from March 2015, whereas modified Thayer Martin medium for gonorrhoea culture was used to diagnosed gonorrhoea before March 2015 [22 (link)]. Individuals who were diagnosed with concurrent gonorrhoea or chlamydia at multiple anatomical sites on the same day were considered a single infection in this analysis. The HIV infections were diagnosed using DiaSorin Liaison XL Murex HIV Ab/Ag CLIA (fourth generation) assay from April 2014 and Abbott Murex HIV-1 2.0 EIA (third generation) before April 2014 and confirmed by the Western blot assay.
