Chlamydia, explained

Chlamydia is the most commonly diagnosed sexually transmitted infection in the UK, and it is a master of keeping quiet. Most people who have it feel completely well. No discharge, no pain, no clue. That sounds like good news and is in fact the trap: an infection you cannot feel is one you do not treat, and one you pass on without knowing. Chlamydia does its real damage precisely because it is boring enough to ignore.

What it can quietly do

Left alone, chlamydia can climb. In women it can ascend from the cervix into the womb and fallopian tubes and cause pelvic inflammatory disease. Around one in seven women with untreated chlamydia goes on to develop PID, and PID is not a trivial thing to have had. At its worst it means severe lower abdominal pain, fever, deep pain during sex, and an illness that can put someone in hospital on a drip of antibiotics. Even after the acute attack settles, it scars the fallopian tubes, and that scarring is permanent. It leaves many women with chronic pelvic pain, a grinding, daily ache that can last for years, flares unpredictably, and is genuinely difficult to treat once established; painkillers manage it rather than cure it. The same scarring is the leading cause of two more serious outcomes: infertility, and ectopic pregnancy, where a pregnancy implants in the damaged tube instead of the womb and can rupture, bleed catastrophically, and kill. None of these can be reversed with antibiotics. Once the tubes are scarred, they stay scarred.

Men are not spectators. Chlamydia can inflame the epididymis, the coiled tube behind the testicle, causing epididymitis, and anyone who has had it does not forget it: a hot, swollen, exquisitely tender testicle, so painful it is sometimes mistaken for a surgical emergency, that can take weeks to settle and can leave a dull chronic ache in the scrotum long after the infection has gone. It can affect fertility. In both men and women chlamydia can also trigger reactive arthritis, an immune overreaction remembered by the grim little rhyme, cannot see, cannot pee, cannot climb a tree, inflaming eyes, urethra and joints at once, and that can drag on for months.

None of this is said to frighten for the sake of it. It is said because the whole point of a two-week test is to catch a silent infection while it is still just an infection, and not yet a scarred tube, a swollen testicle, or a decade of pelvic pain.

How it is found and treated

Because it hides, you test rather than wait. Chlamydia is found by a NAAT test on a urine sample or a self-taken swab, no examination needed. If sex has involved oral or anal contact, a throat or rectal swab is added, because a urine sample cannot find what it never sampled.

Caught early, treatment is a short course of antibiotics, and that genuinely is straightforward. This is the whole argument for testing early, because the moment it has climbed and caused PID or epididymitis, it stops being straightforward. Established PID means longer courses, sometimes two antibiotics at once, sometimes hospital and a drip, and even then the treatment stops the infection without undoing the scarring already done. The cruel arithmetic of chlamydia is that the infection is easy to cure and the damage is not. You are only ever treating early if you test early.

The honest summary

Chlamydia is common and silent, simple to cure in its first weeks, and capable of causing years of pain and permanent infertility once it takes hold. The window where it is easy does not stay open. Testing while you feel well is the only moment you get to catch it while it is still the easy version.