Chlamydia

Bacteria bound to the cell surface, observed by scanning electron microscopy. The bacteria were colored blue. © Maria Eugenia Balañá / Institut Pasteur

Chlamydia is a sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. It is the most widespread bacterial STI, affecting both men and women, and is particularly common among young people. In many cases, the infection is asymptomatic and therefore not diagnosed or treated, which contributes to its spread. Chlamydia can be contracted several times, since acquired immunity against this bacterium is low. It can be transmitted through all types of sexual intercourse including oral and anal sex.

More than 120 million estimated cases every year throughout the world
Two-thirds of cases aged 15 to 25

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Cause

Chlamydia trachomatis is a bacterium specific to humans which can only develop by infecting cells. The bacterium is transmitted sexually, developing in the surface cells of infected tissue.

Symptoms

Most genital infections are asymptomatic. Symptoms experienced by women several weeks after infection include pain during urination or sexual intercourse, yellowy or bloody vaginal discharge, and stomach aches. Symptoms of infection in men include a prickling or burning sensation when urinating or whitish discharge around the penis or rectum. Infected individuals can transmit the infection during sexual intercourse even if they are asymptomatic. Finally, contact with infected secretions can lead to the bacteria infecting and proliferating in the conjunctiva of the eye, resulting in conjunctivitis.

Potential complications

The long-term complications of chlamydia are particularly concerning for women. Untreated Chlamydia trachomatis infections can result in inflammation of the uterus and fallopian tubes, causing infertility or ectopic pregnancy. Chlamydia trachomatis infections may also be passed on from mother to baby at birth, causing pneumonia or eye infections in newborns (conjunctivitis). Untreated Chlamydia trachomatis infections in men can cause inflammation of the prostate, testicles or epididymis. Chlamydia trachomatis infections expose both women and men to increased risk of HIV infection.

Prevention

As with all sexually transmitted infections, systematic condom use is the main means of preventing Chlamydia trachomatis infection (even during oral sex). There is no vaccine against Chlamydia trachomatis infection. In order to break the chain of infection, individuals diagnosed with the infection should alert recent sexual partners (dating back one month) so that they can arrange a screening test.

Epidemiology

Chlamydia trachomatis infection affects the entire global population, with over 120 million estimated cases every year throughout the world. Young adults are most at risk, with approximately two-thirds of cases aged 15 to 25.

Diagnosis and treatment

Chlamydia trachomatis infections are diagnosed in medical testing laboratories through PCR testing of urine samples or samples taken from affected organs (urethra, vagina, rectum, throat). Treatment consists of tetracycline antibiotics (1-week course of doxycycline) or macrolide antibiotics (single dose of azithromycin).

January 2022