Chlamydia is a bacterium (Chlamydia trachomatis). Chlamydia is one of the most common sexually transmitted infections (STI). They most often affect young men and women under the age of 25, as well as men who have sex with men. As the infection often causes no symptoms, many people are unaware that they are carriers of chlamydia. The bacterium can be found in the urethra, pharynx and rectum, as well as in semen, and in low concentrations in urine and pre-ejaculatory fluid. Transmission can occur during fellatio, sexual contact or anal penetration, even if a condom is used at certain times during intercourse. When it does occur, the classic symptoms in the penis are discharge, burning, pain and/or itching of the urethra or anus. If you have symptoms, you can be screened and treated. When the infection persists, it can lead to chronic inflammation of the prostate, testicles or rectum. Chlamydia can be treated with antibiotics. Partner(s) must be screened and/or treated at the same time.

As of November 2023, gay cisgender men are no longer recommended to undergo chlamydia and gonorrhea screening in the absence of symptoms.

The Belgian gonoscreen study showed that asymptomatic chlamydia was harmless to cisgender men, and that it was preferable to let it go on its own rather than treat it systematically with antibiotics. Indeed, frequent use of antibiotics can lead to resistance.

Here are the situations in which chlamydia gonorrhea screening is still recommended:

• You have symptoms
• You've been notified of an STI by a partner 
• You have sexual relations with people who have a uterus (cisgender women, certain transgender men, etc.) or you have a uterus yourself.

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LGV, or lymphogranulomatosis venereum, is a particularly invasive strain of chlamydia that can lead to serious complications in the anal region. That's why it's always advisable to screen the anal region in the presence of symptoms, and to identify the strain of chlamydia if diagnosed, so that treatment can be adapted if necessary.