Chlamydia is one of the most common STD in the Netherlands. At ZIZ, we find chlamydia in around one in six people who get tested. We see it mainly in people under 25.

Chlamydia is so common precisely because it often causes no symptoms. That means you can pass it on without realising it during unprotected sex. When symptoms do appear, they usually involve pain when urinating or unusual discharge. Beyond these milder complaints, women can also develop a more serious inflammation. In the worst cases this causes scarring, which can make it more difficult to get pregnant.

The good news is that chlamydia is easily treated with antibiotics. If you test positive, it's wise to let any sexual partners know they should get tested too. This also lowers your own chance of catching it again after treatment, since having had chlamydia gives you no protection against a new infection.

Chlamydia is an STD caused by the bacterium Chlamydia trachomatis (Ct). There are different types. For STD care, the key distinction is between regular chlamydia and a more aggressive variant that can cause a severe infection, particularly in the anus. This variant is called LGV (lymphogranuloma venereum). In the Netherlands it is seen almost exclusively in men who have sex with men. At ZIZ, if someone in this group tests positive for anal chlamydia, we automatically test further for LGV, free of charge.

You can get chlamydia through sex without a condom, both vaginal (penis–vagina) and anal (penis–anus). You can also get it in your throat through oral sex, though this is less common. Condoms are very effective at preventing chlamydia.

Chlamydia is one of the most common STDs in the Netherlands. At ZIZ, the detection rate is 16% — around one in six people who get tested. We see it mainly in people under 25.

The chance of catching chlamydia during unprotected sex (penis–vagina) is roughly 10% each time you have sex with someone who carries it. Transmission is easier from men to women than the other way around. And if your regular partner turns out to have chlamydia, the chance that you have it too is greater than 50%.

Many people with chlamydia have no symptoms, so relatively little is known about how an untreated infection develops over time. One study found an average infectious period of 1.3 years in people without symptoms. Around half of women who have chlamydia without symptoms clear the infection on their own within a year. After two years this rises to 80%, and after three years to 90%.

Yes, having had chlamydia does not protect you against getting it again. There are even signs that repeated infections increase the risk of complications, possibly because of a stronger immune response each time. This is another reason to tell your partners and to avoid sex for at least a week after finishing your treatment. Doing so prevents the "ping-pong effect," where partners keep reinfecting each other.

About one in ten women with chlamydia has symptoms. When the infection is in the cervix, the symptoms are usually vague: a change in discharge, bleeding between periods, and bleeding or pain during or just after sex. When it's in the urethra, it can feel like a urine infection instead, with symptoms such as needing to urinate more often and pain when urinating.

In women, chlamydia can also travel upwards and cause PID (pelvic inflammatory disease). The chance of this is around two to five per cent. PID often causes abdominal pain, fever and a general feeling of being unwell. Its longer-term consequences 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 STD. 

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.

n the anus, non-LGV chlamydia can cause discharge, irritation, itching, anal pain and diarrhoea. LGV is a more serious form of anal chlamydia which, in the Netherlands, we see almost exclusively in men who have sex with men. With LGV the inflammation can be more severe and also involve 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 30-90 minutes.

If you have no symptoms, we advise waiting at least two weeks after a risk contact, so the test is reliable. If you do have symptoms, you can test sooner. Testing straight after a risk contact isn't useful, because you're still within the incubation period.

At ZIZ, we treat men who have chlamydia in the urethra with a single dose of one gram of azithromycin (two tablets). For men with anal chlamydia and for women, this treatment doesn't always work as well, so we treat those groups with a course of doxycycline, taken twice a day for seven days. Treatment at ZIZ is always free.

f you have symptoms and they turn out to be caused by chlamydia, we advise telling your sexual partners from the past 6 weeks. If you tested positive but had no symptoms, we advise telling your partners from the past 6 months. Notifying them matters: it stops chlamydia spreading further and helps prevent the serious complications a chlamydia infection can cause.

For chlamydia, a test of cure is not necessary. It's also useful to know that the test can stay positive for a few weeks after successful treatment, so if you do want to test again, we advise waiting 4–6 weeks. We do recommend testing again 4–6 months after a positive result, because in that period we sometimes see new infections passed on by untreated partners.