Chlamydia trachomatis

Chlamydia trachomatis serotypes D to K are obligate intracellular bacteria that cause a genital infection with a similar clinical presentation to gonococcal infection. Chlamydia is much more prevalent than gonorrhea and is less confined to inner city areas. Longstanding asymptomatic genital infection is not uncommon: up to 75% of infected people have no symptoms. Establishing a sexual history is therefore important to identify women who are at risk of chlamydial infection.

The rate of chlamydia is highest in sexually active teenagers. High prevalences have also been reported in women seeking termination of pregnancy (Table Prevalence of chlamydial infection in women (19-44 years) reported from various clinical settings in the UK, 1997-2001) and following intrauterine device (IUD) insertion for emergency contraception. In 2001 the reported rate of chlamydia in England was 373/100 000, with higher rates being observed in Greater London and considerably lower ones in East Anglia and the South West of England.

Table Prevalence of chlamydial infection in women (19-44 years) reported from various clinical settings in the UK, 1997-2001

Population Median prevalence (%) Range (%)
General population 1.5 1-2
General practice 4.5 1-12
Gynecology clinics 4.8 3-6
Family planning clinics 5.1 3-7
Women seeking abortions 8.0 7-12
genitourinary medicine clinics 16.4 7-29

Data derived from Chlamydia Trachomatis. Summary and Conclusions of CMO Expert Advisory Group. London: Department of Health

The incubation period of Chlamydia trachomatis is approximately 2 weeks. The main sites of infection are the urethra and cervix, although the pharynx and rectum may also be involved. When present, symptoms include vaginal discharge, mild dysuria, intermenstrual and postcoital bleeding and lower abdominal pain with dyspareunia. Contact bleeding from the cervix may be noted on examination. Pharyngeal and rectal infections are usually asymptomatic, although rectal pain and anal discharge may be reported. Rarely, Chlamydia causes adult conjunctivitis, perihepatitis and sexually acquired reactive arthritis (SARA). When transmitted vertically, the neonate may develop opthalmia or pneumonia. Chlamydia is responsible for the majority of cases of pelvic inflammatory disease. Chlamydia causing only minimal symptoms and signs of pelvic inflammatory disease can cause chronic pelvic pain, tubal damage and subfertility. However, the risk of infertility should not be overemphasized, so that the woman does not discontinue her method of contraception. Chlamydial infection has also been estimated to account for 40% of ectopic pregnancies.

Chlamydia trachomatis: Diagnosis

A number of speciments can be used to test for chlamydia. Trained medical professionals can take swabs from the cervix and urethra. The cervix needs to be cleaned of excess mucus or discharge before swabbing. The cervical swab should be inserted 1-2 cm into the cervix past the squamocolumnar junction and turned several times in order to exfoliate columnar cells. A second swab is taken from the urethra. The urethral swab is inserted 1 cm into the urethra and rotated 1-2 times. Both swabs are usually transported together.

First voided morning urine is an excellent specimen for nucleic acid amplification assay. The first 10-20 ml of the morning urine contain epithelial cells from the urethra and may contain chlamydia. Urine specimens have the advantage of being simple and non-invasive, but specimens need to be maintained at low temperatures during transportation to the laboratory. Vaginal swabs obtained by the patients themselves have also been shown to be good specimens for chlamydia testing.

NAATs such as LCR and PCR are more sensitive than culture tests or enzyme immunoassays (EIA or enzyme-linked immunosorbent assay (ELISA)) and, if available, are the diagnostic methods of choice. LCR and PCR may be useful as screening tests as they can often be carried out on urine specimens, avoiding the need for a vaginal examination. The full potential of these tests is still being evaluated. Direct immunofluorescence (DIF) and culture tests are expensive and unsuitable for analyzing a larger number of specimens. Culture tests are required in forensic cases, such as rape, in view of their high specificity.

Chlamydia trachomatis: Treatment

Uncomplicated chlamydial infection in non-pregnant women should be treated with doxycycline 100 mg orally twice daily for 7 days or azithromycin 1 g orally as a single dose. Women who are pregnant, lactating or who do not tolerate these drugs may be treated with erythromycin stearate 500 mg orally twice daily for 14 days. Erythromycin leads to a slightly lower cure rate than doxycyline, so patients treated in this way should be re-tested three weeks after completing therapy.


In the UK, there is no routine screening for chlamydia. Patients are tested for chlamydia only when it is clinically indicated or to perform opportunistic screening in high-risk groups.

Pelvic inflammatory disease (PID)

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