AKT · Sexual health/Bacterial STIs

Chlamydia

Chlamydia trachomatis (D–K) — obligate intracellular

Overview

The commonest bacterial STI in the UK, frequently asymptomatic. Causes urethritis, cervicitis and can ascend to PID; vertical transmission causes neonatal conjunctivitis and pneumonia.

Recognise

Often asymptomatic (esp. women)
Women: discharge, post-coital/intermenstrual bleeding, dysuria, deep dyspareunia
Men: urethral discharge, dysuria
Complications: PID, epididymo-orchitis, reactive arthritis, Fitz-Hugh–Curtis

Red flags

Pregnancy (neonatal transmission), suspected PID, or systemic features

Differentials & how to tell them apart

Gonorrhoeaoften co-exists; gonorrhoea discharge more purulent — but treat on NAAT, not appearance

Mycoplasma genitaliumpersistent non-gonococcal urethritis after doxycycline — test if available

UTIurine dip/culture; no risk exposure

Investigations

NAAT — vulvovaginal swab (women) or first-pass urine (men); rectal/pharyngeal NAAT per exposure. Test for other STIs incl. HIV/syphilis.

Management

Doxycycline 100 mg BD for 7 days

1Refer to GUM. First-line: doxycycline 100 mg BD for 7 days.Gate: Doxycycline is contraindicated in pregnancy/breastfeeding → use azithromycin 1 g then 500 mg OD for 2 days
2Pregnancy: azithromycin (1 g then 500 mg OD ×2d), or erythromycin, or amoxicillin 500 mg TDS ×7d — with test of cure.
3Ophthalmia neonatorum / neonatal pneumonia: oral erythromycin for the infant.

Doxycycline — first-line; contraindicated in pregnancy/breastfeeding

Azithromycin — if doxycycline contraindicated; used in pregnancy

Erythromycin/amoxicillin — pregnancy alternatives

Key points

Test of cure NOT routine except in pregnancy, rectal infection, or persisting symptoms. Pregnancy needs TOC ~6 weeks.

Monitor & prognosis

Symptom resolution; TOC where indicated; re-test at 3 months (re-infection common).

Excellent with treatment; untreated → tubal infertility, ectopic risk.

Source: NICE CKS Chlamydia (2025); BASHH