Sexually Transmitted Infections (STIs)
Infections transmitted primarily through sexual contact — often asymptomatic but always treatable or manageable.
Overview
STIs include chlamydia, gonorrhoea, syphilis, herpes, trichomoniasis, HPV, hepatitis B/C and HIV. Many are silent yet cause infertility, ectopic pregnancy, cancer or onward transmission. Confidential, free testing is available through sexual-health services.
Symptoms
- • Often none — many infections are asymptomatic
- • Abnormal genital discharge or odour
- • Genital sores, ulcers, blisters or warts
- • Pain on urination or during sex
- • Lower abdominal or pelvic pain; testicular pain
- • Unexplained rash or systemic symptoms (fever, lymphadenopathy)
Risk factors
- • New or multiple sexual partners
- • Inconsistent condom use
- • Men who have sex with men (higher prevalence of certain STIs)
- • Previous STI
- • Recreational drug use including chemsex
Causes
- • Bacterial: chlamydia, gonorrhoea, syphilis, mycoplasma genitalium
- • Viral: HSV, HPV, HIV, hepatitis B/C
- • Parasitic: trichomoniasis, pubic lice, scabies
🚨 Red flags — seek urgent care
- • Severe pelvic pain with fever — pelvic inflammatory disease or sepsis
- • Testicular pain — exclude torsion
- • Painless genital ulcer — exclude syphilis
- • Disseminated rash with joint pain — disseminated gonococcal or secondary syphilis
When to seek care
- • Any new genital symptom
- • After unprotected sex with a new partner
- • Routine annual screen if sexually active under 25 or with new partners
- • Partner notified positive STI
Diagnosis
- • Self-taken vulvovaginal swab or first-pass urine for chlamydia and gonorrhoea (NAAT)
- • Triple-site testing (urethral, pharyngeal, rectal) for MSM
- • Serology: HIV (4th-generation antigen/antibody), syphilis, hepatitis B/C
- • Microscopy or culture for symptomatic vaginal/urethral discharge
- • Window periods: HIV 4 weeks, syphilis 12 weeks for full reassurance
Treatment
- • Chlamydia: doxycycline 100 mg BD × 7 days (first-line)
- • Gonorrhoea: ceftriaxone 1 g IM single dose (test of cure essential due to resistance)
- • Syphilis: benzathine penicillin G IM (regimen by stage)
- • Genital herpes: aciclovir/valaciclovir; suppressive therapy if frequent recurrences
- • Trichomoniasis: metronidazole
- • HIV: combination antiretroviral therapy lifelong
- • Partner notification and treatment essential; abstinence until completed
Prevention
- • Consistent condom use
- • HPV vaccination
- • Hepatitis A and B vaccination for at-risk groups
- • HIV pre-exposure prophylaxis (PrEP) for those at substantial risk
- • Doxycycline post-exposure prophylaxis (doxy-PEP) in selected MSM (emerging evidence)
- • Regular screening when sexually active with new partners
Complications
- • Pelvic inflammatory disease, infertility, ectopic pregnancy
- • Epididymo-orchitis
- • HPV-related cervical, anal and oropharyngeal cancers
- • Mother-to-child transmission in pregnancy
- • Untreated HIV — AIDS and opportunistic infections
Prognosis
Bacterial and parasitic STIs are curable with prompt treatment. Viral STIs are manageable with modern therapy; HIV on suppressive treatment confers near-normal life expectancy and zero transmission risk (U=U).
Education & self-care
Most STIs are easy to test for and treat. Getting tested is a sign of looking after yourself and your partners — and modern services make it quick, free and private.
Frequently asked questions
How often should I get tested?
If sexually active under 25 or with new/multiple partners: annually or with each new partner. MSM and PrEP users: every 3 months.
Is it confidential?
Yes. UK sexual-health services are free and confidential; results aren't shared with your GP without consent.
Which STIs can be cured?
Chlamydia, gonorrhoea, syphilis and trichomoniasis are cured with antibiotics. HIV, herpes and most HPV are controlled but not cured; hepatitis C is now curable with direct-acting antivirals.
How soon should I get tested after exposure?
Chlamydia and gonorrhoea can be detected from 2 weeks after exposure. HIV requires testing at 6 weeks (and again at 3 months) for full reassurance. Syphilis tests turn positive from 3 weeks onwards.
What is PrEP?
Pre-exposure prophylaxis — a daily or on-demand tablet (usually emtricitabine/tenofovir) that reduces HIV acquisition by over 99% when taken correctly.