Chlamydia and gonorrhoea
The two most commonly reported bacterial STIs: how they present, how they are tested for, current treatment including drug resistance, and follow-up.
Chlamydia (Chlamydia trachomatis) and gonorrhoea (Neisseria gonorrhoeae) are bacterial infections passed through vaginal, anal and oral sex, and from birth parent to newborn. Both are curable with antibiotics.
How common they are
- Chlamydia is the most frequently reported bacterial STI in both the US and UK. CDC reported about 1.65 million chlamydia cases in the United States in 2023, and roughly 601,000 gonorrhoea cases.
- UKHSA reported 194,970 gonorrhoea diagnoses in England in 2023, the highest annual figure since records began in 1918, followed by a fall of about 16% in 2024.
- Prevalence is highest in people aged 15–24; CDC estimates around 1 in 20 sexually active young women has chlamydia.
Symptoms
Most infections cause no symptoms at all. CDC and BASHH both estimate that around 70% of chlamydia infections in women and at least 50% in men are asymptomatic, and rectal and throat infections are usually silent. This is why testing rather than symptom-watching is the basis of control.
When symptoms occur they may include discharge, pain on urinating, bleeding between periods or after sex, testicular pain, or rectal pain and discharge. Untreated infection can ascend: chlamydia and gonorrhoea are the leading preventable causes of pelvic inflammatory disease (PID), which is associated with tubal-factor infertility and ectopic pregnancy. A 2018 analysis of the Uppsala cohort found roughly 1 in 5 women with PID experienced later tubal-factor infertility.
Testing
Nucleic acid amplification tests (NAATs) are the standard and detect both organisms from the same sample.
| Site | Sample | Notes |
|---|---|---|
| Genital | Vaginal swab (self-taken is as accurate as clinician-taken) or first-catch urine | Vaginal swab is the preferred sample for people with a vagina |
| Rectal | Self-taken rectal swab | Missed entirely by urine testing |
| Throat | Pharyngeal swab | Common site for gonorrhoea, usually symptomless |
Window period: NAATs reliably detect both infections about 2 weeks after exposure; BASHH advises re-testing at 2 weeks if tested earlier. Extragenital testing matters — multiple studies (including Patton et al., 2014, CDC surveillance) found the majority of rectal and pharyngeal infections in men who have sex with men would be missed by urine testing alone.
Treatment
Guidance changed in the last decade and older advice is out of date.
- Chlamydia: doxycycline 100 mg twice daily for 7 days is now first-line (CDC 2021 STI Treatment Guidelines; BASHH 2018). Single-dose azithromycin 1 g is second-line, because trials showed lower cure rates for rectal infection — the 2021 Dombrowski randomised trial found doxycycline cured 100% of rectal chlamydia versus 74% for azithromycin.
- Gonorrhoea: ceftriaxone by injection, 500 mg (CDC) or 1 g (BASHH 2019) as a single dose. Dual therapy with azithromycin was dropped from CDC guidance in 2020.
Resistance is the live concern. WHO estimates 82 million new gonorrhoea infections a year and lists N. gonorrhoeae as a high-priority antibiotic-resistant pathogen. Ceftriaxone-resistant strains have been reported in England, Austria, France and several Asia-Pacific countries since 2018. Because of this, gonorrhoea treatment should always be followed by a test of cure, usually 2 weeks after treatment (BASHH). Chlamydia does not routinely need a test of cure except in pregnancy or rectal infection.
After treatment
- Avoid sex for 7 days after single-dose treatment, or until a 7-day course is finished and any partner is treated.
- Partner notification covers partners from the past 60 days (or the most recent partner if longer ago).
- Re-test at 3 months. Reinfection is common: CDC cites re-infection rates around 14% within months, driven by untreated partners rather than treatment failure.
Myths
- "I would know if I had it." Most people have no symptoms.
- "A urine test covers everything." It does not cover throat or rectum.
- "One dose of azithromycin still works for everything." Not current guidance.
When to see a clinician
Any new discharge, pelvic or testicular pain, fever with pelvic pain, or bleeding after sex needs same-week assessment. Pelvic pain with fever may be PID and is treated urgently to protect fertility.
Sources
- CDC, Sexually Transmitted Infections Treatment Guidelines, 2021; STI Surveillance, 2023.
- BASHH, Chlamydia trachomatis management guideline, 2018; Gonorrhoea guideline, 2019.
- UKHSA, STI diagnoses in England, 2023 and 2024 reports.
- Dombrowski JC et al., Clinical Infectious Diseases, 2021 (doxycycline vs azithromycin, rectal chlamydia).
- WHO, Global progress report on HIV, viral hepatitis and STIs, 2024.
Educational reference, not medical advice. Every article is community-edited and cites its sources; verify anything that affects your health with a clinician who knows your history.