Chlamydia infection !
Chlamydia is a common sexually transmitted bacterial infection that usually causes no symptoms but can lead to pelvic inflammatory disease and infertility.
Updated 2026-10-30
Structures involved
Tap one to see what it is and open it in 3D.
Microorganisms that cause it
Why it happens
- Outcomes of acute inflammation: resolution, abscess, scar or chronic inflammation
- Uterine tube
- Cervix and vagina: the transformation zone
What it is
A sexually transmitted infection caused by Chlamydia trachomatis that affects men and women. It is usually silent but can infect the cervix, urethra, rectum and eyes and lead to pelvic inflammatory disease and infertility.
Who gets it
The most frequently reported bacterial sexually transmitted infection in many countries, most common under age 25; most infections cause no symptoms. In Medellín, Colombia, PCR found it in 4.1% of asymptomatic women attending cervical cytology at three centres. This page shows the female model; male genital parts are in the male pelvis region.
Causes
- Chlamydia trachomatis serovars D–K (genital infection)
- Serovars L1–L3: lymphogranuloma venereum
- Spread by vaginal, anal or oral sex, and from mother to newborn at birth
Risk factors
- Age under 25
- New or multiple sexual partners
- Inconsistent condom use
- Previous sexually transmitted infection
- Partner with a sexually transmitted infection
Pathophysiology
Chlamydia is an obligate intracellular bacterium with two forms: the infectious elementary body enters columnar cells and becomes a replicating reticulate body, then many elementary bodies are released. The slow, often silent inflammation it causes in the cervix and uterine tubes leads to scarring; repeated infections increase tubal damage.
Classification
- Lower genital tract: cervicitis, urethritis, proctitis
- Upper genital tract: pelvic inflammatory disease, perihepatitis in women; epididymitis in men
- Lymphogranuloma venereum (serovars L1–L3)
- Extragenital: conjunctivitis; neonatal conjunctivitis and pneumonia
- Reactive arthritis
Symptoms and signs
- No symptoms in most women and many men
- Women: vaginal discharge, bleeding after sex or between periods, dysuria, lower abdominal pain
- Mucopurulent cervicitis with a friable cervix
- Men: urethral discharge (often clear or scant) and dysuria; testicular pain with epididymitis
- Rectal infection: discharge, pain or bleeding, often silent
- Lymphogranuloma venereum: painless ulcer, then painful inguinal nodes or severe proctitis
Diagnosis
- Clinical
- Suspected from symptoms, examination or sexual history, but mostly found by screening people at risk.
- Tests
- Nucleic acid amplification tests (NAAT) on vaginal swabs (often self-collected) or first-void urine, plus rectal and pharyngeal swabs by exposure; pregnancy test; testing for gonorrhoea, HIV, syphilis and hepatitis B.
- Imaging
- Not needed for uncomplicated infection; pelvic ultrasound if PID with abscess is suspected.
Differential diagnosis
- Gonorrhoea
- Mycoplasma genitalium infection or trichomoniasis
- Urinary tract infection
- Bacterial vaginosis
- Herpes simplex infection (ulcers)
- Inflammatory bowel disease (proctitis)
Goal of treatment
Cure the infection, prevent complications such as pelvic inflammatory disease and infertility, and stop transmission by treating partners.
Treatment
- Medical
- A course of a tetracycline is first-line in most guidelines; a macrolide is an alternative, and in pregnancy the regimen is chosen from drugs considered safe.
- Medical
- Lymphogranuloma venereum is treated with a longer course of a tetracycline.
- Follow-up
- Partner notification and treatment, avoiding sex until both partners finish treatment, retesting after about three months for reinfection, and test of cure in pregnancy.
Drugs for this condition
Complications
- Pelvic inflammatory disease
- Tubal infertility, ectopic pregnancy and chronic pelvic pain
- Fitz-Hugh–Curtis perihepatitis
- Epididymitis
- Reactive arthritis
- Neonatal conjunctivitis and pneumonia
- Increased risk of HIV acquisition
Prognosis
Antibiotics cure the infection in almost all cases, but reinfection is common; tubal damage from earlier or repeated infections may be permanent.
Prevention
- Consistent condom use
- Regular screening of sexually active women under 25 and others at risk
- Partner treatment
- Screening in pregnancy where recommended
- Sexual health education
Test yourself
Think of the answer, then tap the question to see it.
Why is chlamydia screening recommended for young sexually active women?
Most infections cause no symptoms but can silently damage the uterine tubes, causing infertility and ectopic pregnancy.
What are the two developmental forms of Chlamydia trachomatis?
The infectious extracellular elementary body and the replicating intracellular reticulate body.
Which serovars of Chlamydia trachomatis cause lymphogranuloma venereum?
Serovars L1, L2 and L3.
What is the preferred diagnostic test for genital chlamydia?
Nucleic acid amplification testing (NAAT) on a vaginal swab or first-void urine.
Which antibiotic class is first-line for uncomplicated chlamydia in most guidelines?
A tetracycline, with a macrolide as an alternative.
Related conditions
- Gonorrhoea
- Pelvic inflammatory disease
- Ectopic pregnancy
- Syphilis
- HIV infection and AIDS
- Trichomoniasis
- Bacterial vaginosis
- Epididymitis
- Urinary tract infection (acute cystitis)
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Chlamydia trachomatis Infection (StatPearls (NCBI Bookshelf), 2026); Prevalence of Chlamydia trachomatis in an asymptomatic female population attending cervical cytology services of three healthcare centers in Medellín, Colombia (Biomedica : revista del Instituto Nacional de Salud, 2020) · adapted, CC BY 4.0.
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.
