Chlamydia: From Symptoms to Treatment

A 21-year-old woman attends a sexual health service because she has noticed a change in her vaginal discharge and a small amount of bleeding after sex. She has some mild lower abdominal discomfort but feels otherwise well. She has recently started seeing a new partner and they have not always used condoms. She is worried because the symptoms have been present for several days and asks whether she could have an infection.

What might her symptoms suggest?

There are several possibilities, so we would not diagnose her from the symptoms alone. A change in vaginal discharge and post-coital bleeding can occur with cervicitis, and in a sexually active young adult with a new partner, sexually transmitted infections need to be considered. Chlamydia would be high on the differential, but gonorrhoea can present in a similar way, and the lower abdominal discomfort means we also need to think about whether infection has begun to involve the upper genital tract. Pregnancy, other causes of vaginal discharge and non-infectious causes of post-coital bleeding also need consideration.

Chlamydia is particularly easy to miss because many people have no symptoms at all. When symptoms do occur, they depend on the site of infection. Cervical infection may cause altered discharge, post-coital or intermenstrual bleeding, lower abdominal discomfort or deep dyspareunia. Urethral infection may cause dysuria or discharge, while rectal infection may cause pain, discharge, bleeding or proctitis but is often asymptomatic. In people with penile urethral anatomy, urethritis may present with dysuria or penile discharge. Chlamydia can also be present in the pharynx without causing noticeable symptoms.

What is happening and why?

Chlamydia is caused by Chlamydia trachomatis, a bacterium that has to live and reproduce inside human cells. It has a particular affinity for the epithelial cells lining mucosal surfaces such as the endocervix, urethra and rectum. The infectious form of the organism, called the elementary body, attaches to an epithelial cell and is taken inside. Once there it changes into a reticulate body, which can replicate. After replication, the organism changes back into elementary bodies that can leave the cell and infect neighbouring cells.

The symptoms are largely produced by the inflammatory response to infection. That response is not always strong enough to produce obvious symptoms, which is why someone can carry and transmit chlamydia without knowing they have it. The concern is not simply whether the infection is uncomfortable. If cervical infection persists and ascends through the uterus towards the fallopian tubes, inflammation can develop in the upper genital tract. This is one route to pelvic inflammatory disease (PID). Inflammation of the fallopian tubes, or salpingitis, can damage the ciliated lining and healing may leave scarring or adhesions. That is how an infection that may initially cause very little discomfort can later be associated with tubal-factor subfertility or an increased risk of ectopic pregnancy.

Chlamydia is one of the most common sexually transmitted infections across the UK, with a particularly high burden in younger adults. Surveillance is collected separately in England, Scotland, Wales and Northern Ireland, so there is not one directly comparable UK-wide annual diagnosis figure that tells the whole story. The national reports nevertheless show the same broad clinical picture: chlamydia remains common and a substantial proportion of diagnoses occur in younger age groups. For example, England recorded 151,163 diagnoses in 2025 and Scotland recorded 10,785. The latest published Welsh annual report recorded 7,881 diagnoses in 2024, most frequently among women and people aged 15 to 24. Northern Ireland also maintains separate STI surveillance through its sexual health services and home-testing programme. For a UK nursing student, the useful point is not to memorise four surveillance totals but to recognise chlamydia as a common infection throughout the UK while remembering that testing programmes, service pathways and surveillance arrangements differ between the four nations.

What else would you want to know?

Before thinking about tests, we need a little more of the story. When did the discharge and bleeding begin? Is the abdominal discomfort mild and intermittent, or is it becoming more severe? Has she had fever, nausea, pain during sex or abnormal bleeding at other times? Asking about her last menstrual period, contraception and the possibility of pregnancy is also relevant. If the pain or examination findings suggested PID, management would need to move beyond treating uncomplicated cervical chlamydia.

A sexual history helps us work out both the likelihood of an STI and which anatomical sites may need testing. Ask about recent and previous partners, when she last had sex, condom use and whether vaginal, oral or anal sex has taken place. Previous STIs and previous testing are useful to know, as are any known infections in a partner. The conversation should be matter-of-fact and confidential, with safeguarding considered where appropriate. The purpose is not to judge someone's sexual behaviour. It is to make sure the right tests are taken from the right places and that any partners who may have been exposed can receive appropriate care.

What investigations are recommended?

The standard diagnostic test for chlamydia is a nucleic acid amplification test (NAAT), which detects genetic material from C. trachomatis. For our patient, a vulvo-vaginal swab would usually be the preferred genital sample and can be self-taken. The sites tested should reflect the sexual history, so rectal or pharyngeal samples may also be appropriate following exposure at those sites. In people with penile urethral anatomy, first-catch urine is generally the preferred sample. A negative genital sample cannot exclude infection at a different anatomical site that has not been tested.

Timing needs to be considered as well. If exposure was very recent, an early test may not reliably exclude infection, and current BASHH guidance gives specific advice about repeat testing following recent exposure. A diagnosis of chlamydia should also lead to an offer of appropriate testing for other STIs, including HIV, with the exact screen based on the person's history, sites of exposure and current guidance. For this patient, a pregnancy test would also be appropriate if pregnancy is possible. If her lower abdominal pain or examination raised concern about PID, she would need clinical assessment rather than simply being managed as uncomplicated chlamydia.

How could chlamydia be managed?

For uncomplicated urogenital, rectal or pharyngeal chlamydia, current BASHH guidance recommends doxycycline 100 mg orally twice daily for seven days as first-line treatment when suitable. Pregnancy changes the prescribing decision, so the standard regimen should not simply be applied without checking current guidance and the person's individual circumstances. Suspected PID, epididymo-orchitis or lymphogranuloma venereum also requires different assessment and treatment from uncomplicated chlamydia.

Most people with uncomplicated infection do not need a routine test of cure. There are situations where one is recommended, including pregnancy, persistent symptoms or concern about adherence. A test of cure is different from testing later for reinfection. Someone can be successfully treated and then acquire chlamydia again from an untreated or new infected partner. Current BASHH guidance recommends repeat testing for reinfection in people under 25 between two and six months after treatment.

What should we explain to the patient?

Our patient needs more than a prescription. Explain that chlamydia is common, treatable and frequently causes no symptoms, so a diagnosis does not tell us how long someone has had the infection or exactly when it was acquired. She should understand how to take the antibiotics, what to do if doses are missed or side effects occur, and when to seek further advice if symptoms persist or worsen.

Partner notification is part of treatment because partners may have infection without symptoms and untreated infection can lead to reinfection and further transmission. Sexual health services can support this confidentially. She should also be given clear advice about avoiding sexual contact during the treatment period and until relevant partners have been managed, in line with current BASHH advice. This is also a useful opportunity to discuss condoms, future STI testing and contraception if she wants to, without turning the consultation into a lecture about her sexual behaviour.

What could happen if it is not appropriately managed?

For this patient, the main concern is ascending infection. Cervical chlamydia can progress to PID, and inflammation involving the fallopian tubes can result in scarring that increases the later risk of subfertility and ectopic pregnancy. PID can occasionally be associated with perihepatitis, known as Fitz-Hugh-Curtis syndrome, which can present with right upper quadrant pain. Chlamydia can also be associated with sexually acquired reactive arthritis. In people with penile urethral infection, spread can lead to epididymitis or epididymo-orchitis, producing unilateral scrotal pain and swelling. Acute scrotal pain still requires careful assessment because testicular torsion is an important alternative diagnosis that needs urgent surgical review.

There is also a wider public-health reason to diagnose and treat chlamydia. Because infection is so often asymptomatic, it can continue to pass between sexual partners without anyone realising it is present. Treating the individual while supporting partner notification helps interrupt that chain of transmission and reduces the chance that the patient is reinfected. During pregnancy, untreated infection also has implications for the baby because chlamydia can be transmitted during birth and may cause neonatal conjunctivitis or pneumonia.

A little extra: Koalas get chlamydia too

It sounds like one of those facts that cannot possibly be true, but koalas really can develop chlamydial infection. The main species associated with disease in koalas is Chlamydia pecorum, rather than Chlamydia trachomatis, which causes the human STI we have been discussing. In affected koalas, infection can cause serious eye and urogenital disease, including blindness and infertility, and it has become an important conservation problem in some Australian populations. Researchers have even developed and tested vaccines to protect koalas against chlamydial disease. (Polkinghorne et al., 2013; Desclozeaux et al., 2024)

References

Desclozeaux, M. et al. (2024) ‘Immunisation of koalas against Chlamydia pecorum results in significant protection against chlamydial disease and mortality’. Available at: PubMed.

Polkinghorne, A. et al. (2013) ‘Recent advances in understanding the biology, epidemiology and control of chlamydial infections in koalas’, Veterinary Microbiology, 165(3–4), pp. 214–223. Available at: PubMed.

British Association for Sexual Health and HIV (BASHH) (2026) UK National Guideline for the Management of Infection with Chlamydia trachomatis. Available at: BASHH chlamydia guideline.

British Association for Sexual Health and HIV (BASHH) (2026) Chlamydia patient information leaflet. Available at: BASHH chlamydia patient information.

Darville, T. and Hiltke, T.J. (2010) ‘Pathogenesis of genital tract disease due to Chlamydia trachomatis’, Journal of Infectious Diseases, 201(Suppl 2), pp. S114-S125. doi: 10.1086/652397.

NHS (2024) Chlamydia. Available at: NHS chlamydia information.

UK Health Security Agency (2026) Sexually transmitted infections and screening for chlamydia in England: 2025 report. Available at: UKHSA 2025 STI report.

Public Health Scotland (2026) Sexually transmitted infections in Scotland 2016 to 2025. Available at: Public Health Scotland STI statistics.

Public Health Wales (2025) Sexual Health Trends in Wales: Annual Report 2025. Available at: Public Health Wales sexual health report.

Public Health Agency Northern Ireland (2026) Blood-borne viruses and STIs surveillance. Available at: Northern Ireland STI surveillance.