Chlamydia: symptoms, causes & treatment

Chlamydia is the most common sexually transmitted infection in Belgium and is caused by the bacteria Chlamydia trachomatis. This bacteria settles in the mucous membranes of your body and can infect various parts of your body. The disorder occurs in both women and men and is almost always transmitted through unprotected sexual contacts.

The most prominent feature of chlamydia is that it often proceeds silently. Around 70% of women and 50% of men with chlamydia have no symptoms at all. This makes the condition extra insidious: you can have chlamydia without even knowing it and infect your sex partner (s) without even realizing it.

In Flanders, the number of diagnosed cases of chlamydia is rising sharply. Where in 2002 there were 7.3 cases per 100,000 inhabitants, this number grew to 65 cases in 2016 and as many as 218 cases in 2023, which is probably still an underestimation of the actual number of infections, as many people do not get tested due to the absence of symptoms.

The disorder occurs most frequently in young women between the ages of 15 and 29 and in men between 20 and 40 years. This is due to sexual activity, changing sex partners and the inconsistent use of condoms in these age groups.

Chlamydia is caused by infection with the bacteria Chlamydia trachomatis, and this infection occurs almost exclusively through sexual contact. You contract chlamydia after having unprotected sex with someone who carries the bacteria. This does not matter whether it is vaginal, anal or oral sex: the bacteria can be transmitted in any of these forms of sexual contact.

The chlamydia bacteria can end up in various mucous membranes of your body. During vaginal sex, the mucous membranes of the genitals and urinary tract mainly become infected. During anal sex, the bacteria can infect the anus and rectum, and oral sex can cause an infection in the throat. Your eyes can also become infected, for example if you bring the bacteria from your genitals to your eyes with your hands.

There are a few factors that increase your risk of chlamydia infection. Having changing sex partners increases the risk of infection, just like not using condoms during sexual contacts. Certain groups are at higher risk of chlamydia or are more likely to have complications. This applies, for example, to men who have sex with men, sex workers and trans people.

A special situation occurs during pregnancy. If you are pregnant and have chlamydia, there is a risk that your baby will become infected during delivery. The bacteria can then infect your baby's eyes, making treatment necessary.

It is important to know that chlamydia is not transmitted through ordinary daily contact. You can't contract chlamydia from shaking hands, cuddling, drinking from the same glass, or using the same toilet seat. The bacteria needs direct contact with mucous membranes to pass from one person to another.

The most characteristic thing about chlamydia is precisely the absence of symptoms in many people. However, some of the infected people do develop symptoms. When symptoms occur, this usually occurs one to three weeks after the infection. The symptoms can range from mild to severe and vary between men and women.

Various complaints can occur in women. A common symptom is a burning sensation or pain when urinating. You may also have more discharge from your vagina, or the discharge may change color or smell. Some women experience bleeding after sexual contact or between periods. This is called interim blood loss and can be a signal that something is not right.

Lower abdominal pain is another possible symptom in women. This pain can be vague or severe. Pain during sex can also occur. These symptoms may indicate an infection of the organs in your lower abdomen, such as your uterus, fallopian tubes, or ovaries. This is called pelvic inflammation and requires treatment.

In men, chlamydia often manifest itself differently. A white, slimy fluid coming out of the penis is a possible sign of infection. Pain or burning when urinating also occurs, just like in women. Some men experience pain in their scrotum, which may indicate an inflammation of the epididymis.

When chlamydia is transmitted through anal sex, both women and men can experience anal pain. Bowel movements can become bloody or slimy, and going to the toilet can be painful. When the throat is contaminated by oral sex, most people have no symptoms at all, although the bacteria is present and can be transmitted.

The course of the complaints can vary from person to person. Some people only have mild symptoms that they barely notice, while others experience obvious and annoying symptoms. It is also possible that symptoms temporarily disappear but the infection still remains present. This makes it extra important to get tested if you suspect you have become infected, even if you have no symptoms.

Chlamydia can occur in different parts of your body, depending on the type of sexual contact that infected you. The location of the infection often also determines which complaints you experience.

The most common site where chlamydia occurs is in and around the genitals. In women, the bacteria infects the lining of the vagina and cervix. Hence, the infection can spread further to the uterus, fallopian tubes, and ovaries. This can lead to pelvic inflammation, where you feel vague to severe pain in your abdomen. In men, the bacteria lodges in the urethra and can spread to the epididymis, causing pain in the scrotum.

The urinary tract is closely linked to the genitals and is therefore often infected with them. This explains why both women and men with chlamydia often experience a burning sensation when urinating. The bacteria irritates the mucous membrane of the urinary tract, causing this unpleasant sensation.

When having anal sex, chlamydia can infect the anus and rectum. The mucous membrane of these areas becomes irritated, which can lead to pain, itching, and discharge from the anus. Bloody or slimy stools can also occur. This form of chlamydia occurs in both women and men who have anal sex.

The throat is another possible location of a chlamydial infection. When you have oral sex with someone who is infected, the bacteria can attach to the lining of your throat. The special thing is that a chlamydia throat infection usually causes no symptoms. You won't notice it, but you can pass the bacteria on to others during oral sex or even when kissing intensively.

Finally, your eyes can also become infected with chlamydia. This usually happens indirectly, for example when you touch your infected genitals with your hands and then rub your eyes. In newborn babies, an eye infection can develop during childbirth if the mother has chlamydia. A chlamydia eye infection causes redness, swelling, and discharge from the eye.

The good news is that chlamydia is highly treatable with antibiotics. The treatment is relatively simple and, in most cases, highly effective. However, your doctor will only suggest treatment if it makes sense: if you have symptoms or if you belong to a risk group where chlamydia can lead to complications.

The standard treatment for chlamydia is doxycycline. Here you take 100 mg twice daily for seven days. It is important that you complete the full course, even if your symptoms disappear earlier. This is the only way to be sure that all bacteria have been removed from your body. If you are pregnant, you will receive another treatment because doxycycline is not safe during pregnancy. In that case, you will receive azithromycin: you will then take 2 500 mg tablets once, i.e. 1 gram in total.

During the treatment and the first week afterwards, it is important that you do not have sex. The drugs take time to work, and you can still infect your partner if you have sex again earlier. So wait at least seven days after you start the treatment before having sexual contact again.

In some cases, your doctor may want to check whether the infection has really disappeared after treatment. This mainly happens to pregnant women, as a chlamydial infection during pregnancy has risks for the baby. Even if your symptoms do not disappear after treatment, your doctor will do a control test to see what is going on.

Your sex partner (s) must also be treated, otherwise you will continue to infect each other back and forth. That's why you should inform all your sex partners over the past six months. For many people, this feels uncomfortable, and that is understandable. If you find it difficult to have this conversation yourself, your doctor can also inform your partners anonymously via special services such as Partneralert. This way, they know they need to get tested and treated without your name being mentioned.

In addition to medical treatment, it is wise to take good care of yourself. Taking a rest during treatment helps your body recover. It is also important to have safe sex with condoms in the future, so that you do not become infected again or contract other STIs. Open communication with future sex partners about STIs helps prevent new infections.

There is a lot of misinformation about chlamydia, and it's important to know what doesn't help with treatment. Chlamydia is a bacterial infection that can only be treated with antibiotics. Home remedies, natural remedies, or alternative treatments cannot kill the bacteria and are therefore not effective.

Some people think chlamydia will go away on its own if you wait. This is wrong. Without antibiotics, the bacteria will remain in your body. Even if you have no symptoms, the bacteria is still there and you can infect others. In addition, there is still a risk that the infection will spread to other parts of your body and cause complications.

Washing or rinsing your genitals, vagina, or anus does not help against chlamydia. The bacteria is located deep in the mucous membrane and cannot be washed away with water, soap or showers. Vaginal showers can even be harmful because they disrupt the natural balance of your vaginal flora, making you more susceptible to infections.

Over-the-counter anti-inflammatories or pain relievers can alleviate your symptoms, but they do not treat the underlying infection. This may temporarily make you feel better, but the bacteria remains present and can spread further.

There is also no vaccine against chlamydia. Although scientists are researching this, there is currently no preventive vaccine available. The only effective means of preventing chlamydia is the use of condoms during sexual contact.

Finally, it's a misconception that you become immune to chlamydia after you've had it once. You can become infected with chlamydia again even after you have been successfully treated. Your body does not build lasting immunity against this bacteria, so it remains important to protect yourself during sexual contact.

Is chlamydia contagious?

Yes, chlamydia is highly contagious and is transmitted through sexual contact. You can contract the bacteria when having vaginal, anal, or oral sex with someone who is infected. You can also pass on chlamydia without knowing it, because many people have no symptoms. That's why using condoms is so important.

How long does chlamydia last?

Without treatment, chlamydia stays in your body, sometimes for months or even years. With the right course of antibiotics, the infection usually disappears completely within a week to ten days. However, it is important that you complete the full course as prescribed, even if your symptoms disappear earlier.

Can you prevent chlamydia?

Yes, chlamydia can be largely prevented by always using condoms when having sex. Condoms protect you not only against chlamydia, but also against other sexually transmitted diseases. Open communication with your sex partner about STIs and tests also helps prevent infection.

When to see a doctor

See your doctor if you have pain or burning when you urinate, notice unusual discharge from your genitals, or experience pain in your lower abdomen or scrotum. Even if a sex partner tells you that he or she has chlamydia, it is wise to get tested, even if you have no symptoms.

Does chlamydia come back after treatment?

The infection itself does not return after successful treatment, but you can become infected with chlamydia again. You don't build lasting immunity against the bacteria. If you have unprotected sex again with someone who has chlamydia, you run the risk of becoming infected again.

Can Chlamydia Cause Infertility?

It used to be thought that chlamydia often causes infertility, but recent research shows that this chance is small. Chlamydia infertility only occurs in women who have had obvious symptoms of pelvic inflammation. For most people with chlamydia without symptoms, the risk of infertility is negligible.

1. Health and Science: Chlamydia trachomatis
2. eBPNet (Evidence-Based Practice Network)
3. RIVM: Sexual Health Consultation Roadbook (December 2024)
4. RIVM: Chlamydia testing, The changes at a glance (January 2025)
5. Worel: Diagnosis, Treatment, Monitoring and Referral of Chlamydia Trachomatis Infections (February 2025)
6. Allesoverseks.be: Information about chlamydia
7. Partneralert: Anonymously inform partners about STI URL