Anal chlamydia: symptoms, testing and treatment

Anal chlamydia is a chlamydia infection in the lining of your rectum. It usually causes no symptoms at all, and it does not show up in a urine test. Only a swab of the anus finds it.

That second point is where most people get stuck. You get yourself tested properly, the result comes back clean, and the infection is still there.

Below you will read how that happens, which symptoms do sometimes appear, and what follows a positive result.

What is anal chlamydia?

It is the same bacterium as ordinary chlamydia, Chlamydia trachomatis, just in a different place: the lining of the rectum rather than the urethra or the cervix. The bacterium itself behaves no differently. What changes is how you detect it.

You pick it up through receptive anal contact. That means a penis, but also fingers or toys, and the European guideline names all those routes (de Vries, 2021).

There is one more route that often gets forgotten. In women the bacterium can also reach the rectum without anal sex, carried there by discharge from the vagina.

Which symptoms does anal chlamydia cause?

Usually none. The European guideline states that the majority of rectal chlamydia and gonococcal infections run without symptoms and can only be found with a laboratory test (de Vries, 2021). A study on Reunion island found that every extragenital infection it detected was symptom-free (Calas, 2021).

When there is something, it resembles mild bowel irritation: some mucus, itching, an empty urge, sometimes a streak of blood. Together those symptoms are called proctitis.

They are mild enough that people put them down to something else.

A stressful week, bad food, or haemorrhoids. The full symptom picture and how to work through it is in proctitis: symptoms, causes and testing.

Why does a urine test miss anal chlamydia?

Because a urine test looks at what is in your urethra. The rectum drains nothing into your urine, so an infection there leaves no trace in that sample. The same goes for a blood test, which looks at antibodies rather than at the site of the infection.

This is not an edge case. It is the reason extragenital testing has a research field of its own (Chan, 2016).

The table shows which sample yields what.

Look at the second row. Anyone who only submits urine after receptive anal contact gets a clean result about the wrong place. More explanations for that scenario are in a negative STI test but still symptoms.

How do you get tested for anal chlamydia?

With a swab of the anus, which the lab examines with a PCR. The cotton swab goes a short way into the anal canal and is rotated. It takes seconds, it does not hurt, and you are allowed to do it yourself.

That last part is well studied. In a 2024 study, rectal swabs taken at home were no worse than swabs taken in a healthcare setting (Orser, 2024).

Our test for chlamydia, gonorrhoea and trichomonas uses that same PCR. Choose an anal swab when ordering if that is where your risk sat, because the standard sample looks at the genital side. The practical side is in STIs in the anus and how you test.

On timing: chlamydia can generally be detected reliably after about two weeks. Test earlier and the result may be too early. See how long after unprotected sex you can test.

How is anal chlamydia treated?

With antibiotics, prescribed by a doctor. For rectal chlamydia, doxycycline is generally used rather than a single dose of azithromycin, because doxycycline works better at that site.

We test and do not treat, so that choice sits with your GP or a sexual health clinic.

One detail matters. If the result turns out to be LGV, the course runs longer than for ordinary chlamydia. Why that matters is in LGV: the STI a normal chlamydia test misses. The wider treatment story is in chlamydia treatment.

Should you test again after treatment?

You discuss that with the doctor treating you. A retest can be useful to check the infection has gone, and because reinfection through an untreated partner is common. What that involves is in chlamydia retesting and follow-up.

Retesting too soon has one trap. Remnants of dead bacterial DNA can keep a PCR positive for a while, even once the infection has cleared.

So your doctor picks the moment, not your impatience.

Take two people who tested positive for anal chlamydia on the same day, and who tested again 6 weeks later.

One had their partner treated too, the other did not. Only the second turned out to be reinfected. What I notice here: the course of antibiotics is rarely the problem, the untreated partner almost always is.

The RIVM tracks Dutch STI figures through the sexual health centres, and chlamydia has topped the list of infections found there for years. That it is so common is exactly why the sample has to be taken in the right place.

References

• de Vries HJC, et al. 2021 European Guideline on the management of proctitis, proctocolitis and enteritis caused by sexually transmissible pathogens. Journal of the European Academy of Dermatology and Venereology, 2021. PMID 34057249.
• Chan PA, et al. Extragenital Infections Caused by Chlamydia trachomatis and Neisseria gonorrhoeae: A Review of the Literature. Infectious Diseases in Obstetrics and Gynecology, 2016. PMID 27366021.
• Calas A, et al. Prevalence of urogenital, anal, and pharyngeal infections with Chlamydia trachomatis, Neisseria gonorrhoeae, and Mycoplasma genitalium: a cross-sectional study in Reunion island. BMC Infectious Diseases, 2021. PMID 33478403.
• Orser L, et al. Testing for extragenital Neisseria gonorrhoeae and Chlamydia trachomatis: At-home pharyngeal and rectal self-swabs are non-inferior to those completed in healthcare settings. PLoS One, 2024. PMID 38768150.
• RIVM, STI surveillance Netherlands. Accessed August 2026.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.