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Chlamydia trachomatis

Epidemiology of Infectious Diseases: Chlamydia trachomatis

Causal agent
Chlamydia trachomatis.

Common clinical features
In women symptoms may present as cervicitis and urethritis, which may be complicated by pelvic inflammatory disease, tubal damage, infertility and ectopic pregnancy1.

Up to 70% of infections in women are asymptomatic2. Endocervical chlamydial infection has been associated with increased risk of acquiring HIV infection2.

In men symptoms may present as urethritis, which may be complicated by epididymitis1.

Asymptomatic infection may be found in up to 50% of sexually active men.

Can also infect the eye and cause trachoma: a common cause of blindness in the developing world.


  • Occurs worldwide.
  • Genital Chlamydia infection is the most commonly sexually transmitted infection (STI) diagnosed in genitourinary medicine (GUM) clinics in the UK (Health Protection Agency).
  • The number of uncomplicated Chlamydia diagnoses in GUM clinics has risen steadily since the mid 1990s. In 2005 there were 109,832 newly diagnosed cases of uncomplicated genital Chlamydia infections reported in the UK.
  • In the UK the highest rates of Chlamydia are seen among females aged 16-19 years and among males aged 20-24 years (HPA).
  • Genital chlamydial infection is an important reproductive health problem. An estimated 10-30% of infected women develop pelvic inflammatory disease (PID).


Mode of transmission
Direct sexual contact.

Incubation period
Probably 7-14 days.

Period of Communicability
Until treated.
Limited short-term immunity occurs.

Treatment is with 7 days of doxycycline or erythromycin or a single dose of azithromycin1.

Infected individuals should abstain from sexual intercourse until they and their sexual partners have completed treatment to avoid re-infection.

Prevention and control
The use of condoms reduces the risk of infection.

In the UK screening for genital Chlamydia is offered to all sexually active women


  1. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.
  2. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  3. Department of Health. National Chlamydia Screening programme (NCSP) in England. Department of Health, July 2004. Available at:

© CM Kirwan 2006