O29 Characterising the increase in syphilis in England between 2012 and 2021 by stage of infection at diagnosis

Introduction

Syphilis diagnoses in England continue to rise with distinct but interlinked epidemics among gay, bisexual and other men who have sex with men (GBMSM) and heterosexuals. We aim to understand changes in the distribution of diagnoses by stage over time that may indicate shifts in epidemiology.

Methods

Data on syphilis diagnoses and testing between 2012 and 2021 were obtained from GUMCAD STI Surveillance System. Syphilis stages were defined as infectious syphilis (primary, secondary or early latent) or non-infectious syphilis (late latent). Diagnoses coded as complications relating to untreated syphilis were excluded. Test positivity was defined as all syphilis diagnoses divided by all syphilis tests. We compared trends in the annual distribution of syphilis diagnoses by stage among GBMSM and heterosexuals, the number of tests and test positivity.

Results

The proportion of syphilis diagnoses that were infectious among heterosexuals increased from 38.6% in 2012 to 59.8% in 2021 (Table 1). Testing increased among heterosexuals between 2012 and 2019 (888,341 to 1,152,445), before decreasing to 813,606 in 2021. Test positivity increased from 0.22% in 2012 to 0.28% in 2021. Among GBMSM, the proportion of diagnoses that were infectious remained stable between 2012 and 2021 (mean of 86.9%). The proportion of diagnoses that were early latent increased from 24% in 2012 to 37% in 2021 (Figure 1), whilst the proportion that were primary and secondary decreased. Testing increased from 83,053 in 2012 to 256,795 in 2021.

Discussion

The proportional increase in infectious syphilis diagnoses among heterosexuals indicates that infections are being diagnosed at an earlier stage. This trend could be due to changing testing behaviour or given the increase in test positivity and proportion of symptomatic diagnoses, an increase in recent transmission. Further work is needed to assess the impact of HIV pre-exposure prophylaxis (PrEP) on testing frequency among GBMSM and how that may impact transmission.