Appendix 1- Background information on relevant sexually transmitted infections
Published 7 October 2026
Applies to England
© Crown copyright 2026
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Syphilis
Syphilis is a preventable and readily treatable infection; however, diagnoses have risen substantially in recent years across England. In 2025, 11,839 cases of syphilis were reported. There is evidence of higher prevalence within some inclusion health populations, including sex workers and those in contact with the criminal justice system.
Congenital syphilis continues to pose a serious public health risk. Infection during pregnancy can result in stillbirth, neonatal death or long‑term disability. Cases of congenital syphilis are continuing to be confirmed, indicating ongoing missed opportunities for timely screening, diagnosis and treatment during pregnancy.
The UKHSA Syphilis Response Plan sets out the organisation’s strategic approach to reducing syphilis transmission, preventing adverse health outcomes and addressing the inequalities associated with infection.
Chlamydia
Chlamydia infection is the most diagnosed bacterial sexually transmitted infection (STI) in the UK. Prevalence is highest among young, sexually active individuals, particularly those aged 15 to 24 years.
Chlamydia infection is frequently asymptomatic. However, if left untreated, it can result in significant adverse health outcomes. These include pelvic inflammatory disease (PID), ectopic pregnancy and tubal factor infertility (TFI) in women. Chlamydia therefore represents a substantial and ongoing public health concern.
Lymphogranuloma venereum (LGV) is an invasive form of Chlamydia trachomatis infection that occurs predominantly among men who have sex with men. Additional LGV testing may be indicated for individuals with a positive chlamydia result who have compatible clinical features or epidemiological risk factors.
Gonorrhoea
Gonorrhoea is the second most diagnosed bacterial STI in the UK. Transmission occurs through unprotected vaginal, oral or anal sex, or genital contact with an infected partner. Infection is frequently asymptomatic, enabling ongoing transmission in the absence of diagnosis. If untreated, gonorrhoea can lead to serious health consequences, including PID, ectopic pregnancy and infertility.
Gonorrhoea also presents a growing public health challenge due to the emergence and spread of antimicrobial resistance, including multidrug-resistant strains. This threatens the effectiveness of current treatment options and underscores the need for robust prevention, surveillance and control measures.