Chlamydia is one of the most common STIs in the Netherlands. At ZIZ we find chlamydia in around one in six people who take a test.
We see chlamydia mainly in young people under 25. Chlamydia is so common because it often causes no symptoms. This means you can pass it on to others without realising it if you have unprotected sex.
When there are symptoms, they usually involve pain when urinating or discharge. As well as such mild symptoms, women can also develop a more extensive inflammation. In the worst case this leads to scarring, which can make it harder to become pregnant.
Chlamydia can be treated effectively with antibiotics. If it turns out that you have chlamydia, it is wise to let your sexual partners from the past 6 months know that they should get tested. This reduces the chance of getting chlamydia again after treatment, because having had it does not protect you against a new infection.

Chlamydia is an STI. It is caused by the bacterium Chlamydia trachomatis (Ct). There are different types of chlamydia. For STI care, the main thing to know is that there is regular chlamydia and a more serious variant that can cause a more severe infection, particularly in the anus. We call this variant LGV (lymphogranuloma venereum). In the Netherlands we see this exclusively in men who have sex with men. At ZIZ, if someone in this group tests positive for anal chlamydia, we test further for LGV free of charge.

You can get chlamydia through sex without a condom (penis–vagina, penis–anus). You can also get it in your throat through oral sex, but this is less common. Using a condom is very effective at preventing chlamydia.

Chlamydia is one of the most common STIs in the Netherlands. The detection rate for chlamydia at ZIZ is 16%, so around one in six.
We see chlamydia mainly in young people under 25. 

The chance of getting chlamydia during unprotected sex (penis–vagina) is around 10% each time you have sex with someone who carries chlamydia. Transmission happens more easily from men to women than the other way round. If your regular partner turns out to have chlamydia, the chance that you have chlamydia is greater than 50%.

Many people with chlamydia have no symptoms, so not much is known about the natural course of an untreated chlamydia infection. One study found an average infectious period of 1.3 years in people without symptoms. About half of women with chlamydia and no symptoms clear the infection themselves within one year. After two years this is 80% and after three years 90%.

Yes, having had an infection does not protect you against a new one. There are even indications that having several infections increases the risk of complications, possibly because of a stronger immune response. This is another reason why it is important to tell your partners and to avoid sex for at least one week after your treatment. This prevents the ping-pong effect, where sexual partners keep reinfecting each other with chlamydia.

About one in ten women with chlamydia has symptoms. If it is an infection of the cervix, the symptoms are usually not very clear: a change in discharge, bleeding between periods and bleeding or pain during or just after sex. If the infection is in the urethra, it can also feel like a urine infection, with symptoms such as needing to urinate more often and/or pain when urinating.   

In women, chlamydia can also cause an ascending infection leading to PID (pelvic inflammatory disease). The chance of this is around two to five per cent. The symptoms of PID often include abdominal pain, fever and feeling generally unwell. The consequences of PID can include chronic abdominal pain, reduced fertility and ectopic pregnancies.

Chlamydia can cause infertility in women, but the chance of this is smaller than was previously thought. 
For this reason, from January 2025 the GGD no longer routinely tests for chlamydia in people without symptoms that fit an STI. 

In short: 
- If you have a chlamydia infection without symptoms, the impact on your fertility is negligible.
- If you have a chlamydia infection with symptoms, this can lead to reduced fertility, but the chance is still low.
- If you have several chlamydia infections with symptoms, the chance of reduced fertility becomes considerably higher.

The chance that you, as a woman, develop symptoms from a chlamydia infection is around one in ten. The difficulty is that we cannot tell in advance who will develop symptoms from their chlamydia infection and who will not. The chance of serious consequences is small, but the impact can potentially be great. For this reason, at ZIZ we follow the GP guideline and do test for chlamydia. 

In men with chlamydia in the urethra, chlamydia causes symptoms in about half of cases. The other half do not notice that they have chlamydia. The symptoms mainly consist of a burning sensation when urinating. You may also notice a watery or pus-like discharge from the penis, especially in the morning. In some cases chlamydia causes inflammation of the epididymis, which causes pain in your scrotum.

In the anus, non-LGV chlamydia can cause symptoms such as discharge, irritation, itching, anal pain and diarrhoea. LGV is a more serious form of chlamydia in the anus which, in the Netherlands, we see almost exclusively in men who have sex with men. With LGV there can be a more severe inflammation that also involves the local lymph nodes.

In men, we test for chlamydia in the urine. It is important that we collect the first part of the urine stream and that, ideally, you have not urinated for 1 hour beforehand. Women take a swab from the vagina themselves. We then test for the presence of chlamydia using a PCR test. What is unique about ZIZ is that we use one of the fastest PCR tests available, which means we have a result in 90 minutes.

If you have no symptoms, we advise waiting at least two weeks so that the test is reliable. If you do have symptoms, you can test sooner. Testing immediately after a risk is not useful, because you are still within the incubation period.

In men with chlamydia in the urethra, we treat at ZIZ with a single dose of one gram of azithromycin (two tablets). For men with anal chlamydia and for women, this treatment does not always work as well. We therefore treat those groups with a course of doxycycline, which must be taken twice a day for seven days. Treatment at ZIZ is always free. 

If you have symptoms and it turns out that they were caused by chlamydia, we advise telling your sexual partners from the past 6 weeks. If you have no symptoms but still tested positive for chlamydia, we advise telling your sexual partners from the past 6 months. It is important to tell your partners in order to prevent chlamydia spreading further and to prevent serious complications resulting from a chlamydia infection.

For chlamydia this is not necessary. It is also good to know that the test can remain positive for a few weeks after successful treatment. If you do want to test again, we advise waiting until 4–6 weeks afterwards. We do advise testing again 4–6 months after a positive test, because in this period we sometimes see new infections caused by untreated partners.