Overview

Chlamydia infection is a common bacterial sexually transmitted infection primarily caused by Chlamydia trachomatis. The name derives from the Greek word χλαμύδος (cloak) and can also refer to infections produced by other species in the bacterial family Chlamydiaceae. Although many infected people do not notice symptoms, untreated infection may lead to significant reproductive and ocular complications. Effective treatment exists, typically based on antibiotics.

Biology and strains

Chlamydiae are obligate intracellular bacteria that survive and reproduce only inside host cells. Their life cycle alternates between an infectious, extracellular elementary body and a noninfectious, metabolically active reticulate body. Within the species that affect humans, different serovars are associated with distinct clinical syndromes: ocular strains (classically linked to trachoma), genital strains that cause urogenital infection, and invasive strains that cause lymphogranuloma venereum (LGV).

Transmission and epidemiology

Genital chlamydia is transmitted through sexual contact — including vaginal, anal and oral sex — and from mother to infant during vaginal childbirth. Perinatal transmission may lead to neonatal conjunctivitis or pneumonia when a pregnant person is infected. Chlamydia is one of the most frequently reported bacterial sexually transmitted infections worldwide; many national public health agencies publish regular case counts and surveillance data to guide prevention efforts (national estimates are commonly cited).

Clinical features and complications

Many infections are asymptomatic. When symptoms occur, they differ by site and sex. Common presentations include:

  • Genital: urethral discharge or dysuria in men; abnormal vaginal discharge, pelvic pain, or intermenstrual bleeding in women.
  • Rectal: anal pain, discharge or bleeding after receptive anal intercourse.
  • Ocular: conjunctivitis following exposure; repeated or severe ocular disease caused by certain strains is known as trachoma and has been a major cause of infectious blindness historically (trachoma, linked to blindness in affected populations).

If untreated, genital infection can ascend in women to cause pelvic inflammatory disease (PID), increasing the risk of infertility, ectopic pregnancy and chronic pelvic pain. In men, complications can include epididymitis and, rarely, infertility. Neonates exposed at birth may develop conjunctivitis or pneumonia within weeks.

Diagnosis and management

Modern diagnosis relies on nucleic acid amplification tests (NAATs) performed on urine or swab samples; these tests are sensitive and specific and are preferred over older culture methods. First-line therapy for uncomplicated urogenital chlamydia typically uses oral antibiotics; public health guidance commonly recommends single-dose or short-course regimens tailored to age, pregnancy status and coexisting infections. Partner notification and treatment of recent sexual contacts are essential to prevent reinfection and onward transmission.

Prevention and public health

Prevention combines safer-sex practices, accessible testing, and routine screening for people at higher risk. Recommended measures include:

  • Consistent condom use and reduced number of sexual partners.
  • Regular screening of sexually active young people and those with new or multiple partners; many programs target annual testing for sexually active women under 25.
  • Timely treatment of diagnosed individuals and their partners, and counseling on abstaining from sex until therapy is complete.

Public health campaigns also address ocular chlamydia (trachoma) through community-based sanitation, mass treatment in endemic areas, and environmental improvements. For more detailed guidance on clinical care, surveillance and prevention strategies consult trusted health sources and local public health agencies (background, pathogen, treatment options, related species, taxonomy, epidemiology data, vaginal transmission, anal transmission, oral transmission, perinatal risks, birth transmission, trachoma control, vision impact).