Chlamydia

Chlamydia is caused by Chlamydia trachomatis, an obligate intracellular bacterium that can only replicate inside host cells. It has a two-stage life cycle: the elementary body is the infectious, metabolically inert form that attaches to and enters columnar epithelial cells; once inside, it converts to a reticulate body, divides within a membrane-bound inclusion, then reconverts and is released to infect neighbouring cells. That cycle takes two to three days, which is part of why treatment requires an antibiotic that penetrates cells and persists.

The organism targets columnar epithelium, which determines where it causes disease: the endocervix, urethra, rectum, conjunctiva and pharynx. Serovars D through K cause genital infection; serovars A to C cause trachoma, the leading infectious cause of blindness worldwide; and L1 to L3 cause lymphogranuloma venereum.

Transmission is by unprotected vaginal, anal or oral sex, and vertically from mother to infant during delivery. It is the most commonly reported bacterial sexually transmitted infection, and prevalence is highest under the age of 25. The tissue damage is largely immune-mediated rather than directly toxic — the chronic inflammatory response to persistent or repeated infection is what scars the fallopian tubes, which is why repeat infections carry disproportionate risk.

The defining clinical feature of chlamydia is that most infections produce no symptoms at all — roughly 70% in women and 50% in men. This is precisely what makes it dangerous: untreated infection continues to damage tissue and to be transmitted.

In women, symptoms when present include increased or altered vaginal discharge, dysuria, intermenstrual or postcoital bleeding, deep dyspareunia, and lower abdominal pain. Examination may show a friable, inflamed cervix that bleeds on contact.

In men, urethral discharge — typically clearer and thinner than in gonorrhea — with dysuria and urethral irritation. Epididymo-orchitis presents as unilateral testicular pain and swelling.

In both, rectal infection causes pain, discharge and tenesmus or nothing at all, and pharyngeal infection is almost always asymptomatic. Reactive arthritis, with conjunctivitis and urethritis, is an uncommon post-infectious complication.

Untreated chlamydia ascends. In women it causes pelvic inflammatory disease, and the scarring that follows is the principal cause of tubal factor infertility and ectopic pregnancy; chronic pelvic pain is a further consequence. Perihepatitis — Fitz-Hugh–Curtis syndrome — produces right upper quadrant pain from inflammation of the liver capsule.

In pregnancy, infection is associated with preterm delivery and low birth weight, and vertical transmission causes neonatal conjunctivitis and pneumonia. In men, epididymitis is the main complication; effects on fertility are much less clear-cut than in women.

Nucleic acid amplification testing is the diagnostic standard and is far more sensitive than culture. A first-void urine sample is used in men; a vulvovaginal swab, which can be self-taken, is preferred in women. Rectal and pharyngeal swabs are needed where those sites are exposed, since a genital test will not detect them.

Because infection is usually silent, diagnosis depends on screening rather than on symptoms. Testing for gonorrhea, syphilis, HIV and other sexually transmitted infections should be offered alongside, and contact tracing of partners is an essential part of management. A test of cure is not routine in uncomplicated genital infection but is recommended in pregnancy and in rectal infection. Retesting three months after treatment is advised, since reinfection is common.