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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Chlamydia (C. trachomatis): most common bacterial STI in UK (peak 15-24 years). Often asymptomatic. Diagnose with NAAT. Treat with doxycycline 100 mg BD for 7 days (first-line, changed from azithromycin)
- Gonorrhoea (N. gonorrhoeae): urethral discharge, dysuria. Diagnose with NAAT + culture (for sensitivities). Treat with IM ceftriaxone 1g single dose. Rising antimicrobial resistance is a major concern
- Syphilis (Treponema pallidum): three stages — primary (painless chancre), secondary (rash including palms/soles, condylomata lata), tertiary (gumma, aortitis, neurosyphilis). Diagnose with treponemal serology. Treat with IM benzathine penicillin
- All STI patients: full STI screen (chlamydia, gonorrhoea, syphilis, HIV, Hep B/C), partner notification, condom advice, test of cure for gonorrhoea
- Pelvic inflammatory disease (PID): complication of ascending chlamydia/gonorrhoea — lower abdominal pain, cervical excitation, fever. Treat empirically with IM ceftriaxone + oral doxycycline + oral metronidazole
Overview
Sexually transmitted infections (STIs) are a major public health concern globally and in the UK. The most common bacterial STIs are chlamydia, gonorrhoea, and syphilis. Viral STIs include HIV, herpes simplex (HSV-2 and HSV-1), human papillomavirus (HPV), and hepatitis B. Many STIs are asymptomatic, making screening and partner notification critical. All suspected STI cases should ideally be managed through GUM (genitourinary medicine) or sexual health clinic services, which provide confidential testing, treatment, partner notification, and sexual health promotion.
Epidemiology
Chlamydia is the most commonly diagnosed STI in England, with approximately 150,000 cases per year. Gonorrhoea rates have risen significantly (particularly in MSM populations). Syphilis has seen a resurgence, with cases increasing dramatically since 2012. The National Chlamydia Screening Programme targets sexually active under-25s. Online STI testing services have expanded access significantly. Antimicrobial resistance in N. gonorrhoeae is a critical global health threat.
Clinical Features
Symptoms
Chlamydia: often ASYMPTOMATIC (70% women, 50% men). When symptomatic: vaginal/urethral discharge, dysuria, intermenstrual/postcoital bleeding
Gonorrhoea: purulent urethral discharge and dysuria in men (usually symptomatic). Women often asymptomatic or mild symptoms
Syphilis — primary: painless genital ulcer (chancre) with inguinal lymphadenopathy (2-6 weeks post-exposure)
Syphilis — secondary: widespread symmetrical macular/papular rash (classically involves palms and soles), condylomata lata (flat moist warts), fever, lymphadenopathy, oral snail-track ulcers
Genital herpes: painful vesicles/ulcers, dysuria, inguinal lymphadenopathy (primary more severe than recurrences)
Lower abdominal pain, deep dyspareunia, fever (PID — ascending infection)
Signs
Urethral or vaginal discharge (mucopurulent — gonorrhoea; clear/white — chlamydia)
Painless genital ulcer (syphilis chancre — indurated, clean base)
Painful genital vesicles/ulcers (herpes simplex)
Palmar/plantar rash (secondary syphilis — classic exam finding)
Cervical excitation/motion tenderness on bimanual examination (PID)
Reactive arthritis (Reiter syndrome): conjunctivitis + urethritis + reactive arthritis — post-chlamydial
Investigations
First-line
NAAT (nucleic acid amplification test)For chlamydia and gonorrhoea — first-void urine (men) or vulvo-vaginal swab (women, self-taken is preferred). Most sensitive test. Also pharyngeal and rectal swabs in MSM
Syphilis serologyTreponemal tests: EIA/TPHA (specific — remain positive for life). Non-treponemal tests: RPR/VDRL (correlate with disease activity, fall with treatment — used for monitoring)
HIV testOffer to ALL patients attending for STI screening
Second-line
Gonorrhoea cultureIn addition to NAAT — essential for antimicrobial sensitivity testing given rising resistance. Endocervical or urethral swab onto selective media
Hepatitis B and C serologyPart of full STI screen, especially in MSM, IVDU, and those from endemic areas
HSV PCRSwab from vesicle/ulcer base — more sensitive than viral culture. Type-specific (HSV-1 vs HSV-2)
Dark-field microscopyVisualises Treponema pallidum from chancre exudate — rarely performed now, replaced by PCR
Specialist
Pelvic USSIf tubo-ovarian abscess suspected as complication of PID
Lumbar punctureIf neurosyphilis suspected: CSF for VDRL, protein, cell count, FTA-ABS
1
Chlamydia
- First-line: doxycycline 100 mg BD for 7 days (BASHH 2018 update — now preferred over azithromycin due to higher cure rates, especially for rectal chlamydia)
- Alternative: azithromycin 1g stat then 500 mg OD for 2 days (if doxycycline contraindicated)
- Test of cure not routinely needed UNLESS pregnant, rectal infection, or persistent symptoms. Retest at 3-6 months to detect reinfection
- Partner notification: all sexual contacts in last 4 weeks (or most recent if >4 weeks ago)
2
Gonorrhoea
- IM ceftriaxone 1g single dose (BASHH first-line)
- Test of cure at 2 weeks is ESSENTIAL for gonorrhoea (due to resistance concerns)
- Partner notification: all contacts in last 2 weeks (symptomatic) or 3 months (asymptomatic)
- Always test for concurrent chlamydia (co-infection is common ~40%)
3
Syphilis
- Early syphilis (primary, secondary, early latent <2 years): IM benzathine penicillin G 2.4 MU single dose
- Late latent or tertiary syphilis: IM benzathine penicillin G 2.4 MU weekly for 3 weeks
- Neurosyphilis: IV benzylpenicillin 3-4 MU every 4 hours for 14 days
- Jarisch-Herxheimer reaction: fever, headache, myalgia within 24 hours of treatment (cytokine release from dying spirochaetes) — warn patient, manage supportively
- Monitor: RPR/VDRL should decline 4-fold by 6-12 months post-treatment
4
PID (pelvic inflammatory disease)
- Treat empirically if clinical suspicion (do not delay for results): IM ceftriaxone 1g stat + oral doxycycline 100 mg BD 14 days + oral metronidazole 400 mg BD 14 days
- Admit if: severe systemic illness, surgical emergency cannot be excluded, tubo-ovarian abscess, pregnancy
- Complications: tubo-ovarian abscess, chronic pelvic pain, ectopic pregnancy, infertility
Complications
- PID: From ascending chlamydia/gonorrhoea → tubal damage → infertility (10-20% after single episode), ectopic pregnancy, chronic pelvic pain
- Epididymo-orchitis: In men — chlamydia/gonorrhoea in <35 years; E. coli/coliforms in >35 years
- Reactive arthritis: Post-chlamydial — asymmetrical large joint arthritis, conjunctivitis, urethritis. HLA-B27 association
- Neonatal complications: Chlamydia → neonatal conjunctivitis, pneumonia. Gonorrhoea → ophthalmia neonatorum. Syphilis → congenital syphilis
- Neurosyphilis: Tabes dorsalis (dorsal column degeneration), Argyll Robertson pupils (accommodate but do not react), general paresis of the insane (dementia)
UKMLA Exam Tips
- 1Doxycycline 100 mg BD for 7 days is now FIRST-LINE for chlamydia (not azithromycin 1g stat — that is now second-line)
- 2Painless genital ulcer = syphilis chancre. Painful ulcers = herpes. This is a classic SBA discriminator
- 3Rash involving palms AND soles = think secondary syphilis (very few rashes do this — also consider Hand-Foot-Mouth, Rocky Mountain spotted fever)
- 4Gonorrhoea: ALWAYS culture (in addition to NAAT) for sensitivities — antimicrobial resistance is a global emergency
- 5Test of cure: essential for GONORRHOEA, NOT routinely needed for chlamydia (unless pregnant/rectal)
- 6Jarisch-Herxheimer reaction after syphilis treatment: warn patients — fever and worsening symptoms within 24 hours is expected, not a treatment failure
- 7Reactive arthritis triad: urethritis + conjunctivitis + arthritis = "Can't see, can't pee, can't climb a tree"
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