(P428) Increased syphilis testing and detection of late latent syphilis among women after switching from an opt-in to opt-out testing strategy in an urban Australian sexual health clinic

Background: In Australia, a sharp increase in syphilis cases among heterosexual men and women has been identified as a public health priority due to its association with congenital syphilis which is complicated by congenital defects, prematurity, low birth weight and stillbirth. Timely testing, diagnosis and treatment are important to prevent and control syphilis. The Melbourne Sexual Health Centre (MSHC) implemented an opt-out syphilis test for women in December 2017. We aimed to examine the differences in syphilis testing uptake among women after switching from an opt-in to an opt-out testing strategy.

Methods: This was a retrospective study examining all women attending the MSHC for the first time in periods of opt-in (2015-2017) and opt-out (2018-2020) syphilis testing. We calculated the proportion of women who tested for syphilis in each period. Additional analyses were performed among women with urogenital chlamydia testing as a proxy indicator of sexual risk. Multivariable logistic regression was performed to identify factors associated with syphilis testing in the opt-out period.

Results: The mean age of the 27,481 women was 26.8 years (standard deviation=6.9). The proportion of women who were tested for chlamydia who were also tested for syphilis increased from 55.9% (6,676/11,949) in the opt-in period to 71.8% (9,515/13,254) in the opt-out period (p < 0.001) (Table 1). Syphilis positivity did not differ between the two periods (0.49% [33/6676] vs 0.73% [69/9515], p=0.070). The proportion of cases that were late latent increased significantly from 36.4% (12/33) in the opt-in to 60.9% (42/69) in the opt-out period (p=0.033); while the proportion of primary (p=0.342), secondary (p=0.766) and early latent (p=0.055) syphilis did not differ between the two periods. Women aged 16-24 years old (aOR=0.60, 95%CI: 0.46-0.77), and women who engaged in condomless sex (aOR=0.85, 95%CI: 0.75-0.97) were less likely to be tested for syphilis during the opt-out period.

Conclusion: The opt-out testing strategy increased syphilis testing among women with increased detection of asymptomatic late latent syphilis. Further studies are required to understand why young women and those reporting condomless sex are more likely to opt out of syphilis testing. Health education and awareness may be required to improve syphilis testing uptake.