|Classification and external resources|
Pap smear showing C. trachomatis (H&E stain)
Chlamydia infection (from the Greek, χλαμύδα meaning "cloak") is a common sexually transmitted infection in humans caused by the bacterium Chlamydia trachomatis. The term Chlamydia infection can also refer to infection caused by any species belonging to the bacterial family Chlamydiaceae. C. trachomatis is found only in humans. Chlamydia is a major infectious cause of human genital and eye disease. Chlamydia infection is one of the most common sexually transmitted infections worldwide; it is estimated that about 1 million individuals in the United States are infected with chlamydia.
C. trachomatis is naturally found living only inside human cells. Chlamydia can be transmitted during vaginal, anal, or oral sex, and can be passed from an infected mother to her baby during childbirth. Between half and three-quarters of all women who have a chlamydia infection of the cervix (cervicitis) have no symptoms and do not know that they are infected. In men, infection of the urethra (urethritis) is usually symptomatic, causing a white discharge from the penis with or without pain on urinating (dysuria). Occasionally, the condition spreads to the upper genital tract in women (causing pelvic inflammatory disease) or to the epididymis in men (causing epididymitis). Chlamydia infection can be effectively cured with antibiotics. If left untreated, chlamydial infections can cause serious reproductive and other health problems with both short-term and long-term consequences.
Signs and symptoms
Chlamydia is known as the "Silent Epidemic" because in women, it may not cause any symptoms in 70–80% of cases, and can linger for months or years before being discovered. Symptoms that may occur include unusual vaginal bleeding or discharge, pain in the abdomen, painful sexual intercourse (dyspareunia), fever, painful urination or the urge to urinate more frequently than usual (urinary urgency).
In men, chlamydia shows symptoms of infectious urethritis (inflammation of the urethra) in about 50% of cases. Symptoms that may occur include: a painful or burning sensation when urinating, an unusual discharge from the penis, swollen or tender testicles, or fever. Discharge, or the purulent exudate, is generally less viscous and lighter in color than for gonorrhea. If left untreated, it is possible for chlamydia in men to spread to the testicles causing epididymitis, which in rare cases can cause sterility if not treated within 6 to 8 weeks. Chlamydia is also a potential cause of prostatitis in men, although the exact relevance in prostatitis is difficult to ascertain due to possible contamination from urethritis.
Chlamydia conjunctivitis or trachoma was once the most important cause of blindness worldwide, but its role diminished from 15% of blindness cases by trachoma in 1995 to 3.6% in 2002. The infection can be spread from eye to eye by fingers, shared towels or cloths, coughing and sneezing and eye-seeking flies. Newborns can also develop chlamydia eye infection through 
Chlamydia may also cause reactive arthritis (reiter's syndrome)—the triad of arthritis, conjunctivitis and urethritis (inflammation of the urethra)—especially in young men. About 15,000 men develop reactive arthritis due to chlamydia infection each year in the U.S., and about 5,000 are permanently affected by it. It can occur in both sexes, though is more common in men.
As many as half of all infants born to mothers with chlamydia will be born with the disease. Chlamydia can affect infants by causing spontaneous abortion; premature birth; conjunctivitis, which may lead to blindness; and pneumonia. Conjunctivitis due to chlamydia typically occurs one week after birth (compared with chemical causes (within hours) or gonorrhea (2–5 days)).
Chlamydia trachomatis is also the cause of lymphogranuloma venereum, an infection of the lymph nodes and lymphatics. It usually presents with genital ulceration and swollen lymph nodes in the groin, but it may also manifest as proctitis (inflammation of the rectum), fever or swollen lymph nodes in other regions of the body.
Chlamydia can be transmitted during vaginal, anal, or oral sex. Chlamydia can also be passed from an infected mother to her baby during vaginal childbirth.
Chlamydiae have the ability to establish long-term associations with host cells. When an infected host cell is starved for various nutrients such as 
The starved chlamydiae enter a persistent growth state wherein they stop cell division and become morphologically aberrant by increasing in size. Persistent organisms remain viable as they are capable of returning to a normal growth state once conditions in the host cell improve.
There is much debate as to whether persistence has in vivo relevance. Many believe that persistent chlamydiae are the cause of chronic chlamydial diseases. Some antibiotics such as β-lactams can also induce a persistent-like growth state, which can contribute to the chronicity of chlamydial diseases.
For sexually active women who are not pregnant, screening is recommended in those under 25 and others at risk of infection. Risk factors include a history of chlamydial or other sexually transmitted infection, new or multiple sexual partners, and inconsistent condom use. For pregnant women, guidelines vary: screening women with age or other risk factors is recommended by the U.S. Preventive Services Task Force (USPSTF) (which recommends screening women under 25) and the American Academy of Family Physicians (which recommends screening women aged 25 or younger). The American College of Obstetricians and Gynecologists recommends screening all at risk, while the Centers for Disease Control and Prevention recommend universal screening of pregnant women. The USPSTF acknowledges that in some communities there may be other risk factors for infection, such as ethnicity. Evidence-based recommendations for screening initiation, intervals and termination are currently not possible. There is no universal agreement on screening men for chlamydia.
In England and Wales the NHS aims to
- Prevent and control chlamydia infection through early detection and treatment of asymptomatic infection;
- Reduce onward transmission to sexual partners;
- Prevent the consequences of untreated infection;
- Test at least 25 percent of the sexually active under 25 population annually.
The diagnosis of genital chlamydial infections evolved rapidly from the 1990s through 2006. Nucleic acid amplification tests (NAAT), such as polymerase chain reaction (PCR), transcription mediated amplification (TMA), and the DNA strand displacement amplification (SDA) now are the mainstays. NAAT for chlamydia may be performed on swab specimens sampled from the cervix (women) or urethra (men), on self-collected vaginal swabs, or on voided urine. NAAT has been estimated to have a sensitivity of approximately 90% and a specificity of approximately 99%, regardless of sampling from a cervical swab or by urine specimen. In women seeking an STI clinic and a urine test is negative, a subsequent cervical swab has been estimated to be positive in approximately 2% of the time.
At present, the NAATs have regulatory approval only for testing urogenital specimens, although rapidly evolving research indicates that they may give reliable results on rectal specimens.
Because of improved test accuracy, ease of specimen management, convenience in specimen management, and ease of screening sexually active men and women, the NAATs have largely replaced culture, the historic gold standard for chlamydia diagnosis, and the non-amplified probe tests. The latter test is relatively insensitive, successfully detecting only 60–80% of infections in asymptomatic women, and often giving falsely positive results. Culture remains useful in selected circumstances and is currently the only assay approved for testing non-genital specimens.
C. trachomatis infection can be effectively cured with antibiotics once it is detected. Current guidelines recommend azithromycin, doxycycline, erythromycin, or ofloxacin. Agents recommended for pregnant women include erythromycin or amoxicillin.
An option for treating partners of patients (index cases) diagnosed with chlamydia or gonorrhea is patient-delivered partner therapy (PDT or PDPT), which is the clinical practice of treating the sex partners of index cases by providing prescriptions or medications to the patient to take to his/her partner without the health care provider first examining the partner.
Globally, as of 2010, sexually transmitted chlamydia affects approximately 215 million people (3.1% of the population). It is more common in women (3.8%) than men (2.5%). In that year it resulted in about 1,200 deaths down from 1,500 in 1990.
CDC estimates that there are approximately 2.8 million new cases of chlamydia in the United States each year and that it affects around 2% of young people in that country. Chlamydial infection is the most common bacterial sexually transmitted infection in the UK.
Chlamydia causes more than 250,000 cases of epididymitis in the U.S. each year. Chlamydia causes 250,000 to 500,000 cases of PID every year in the United States. Women infected with chlamydia are up to five times more likely to become infected with HIV, if exposed.
Recent phylogenetic studies have revealed that Chlamydia likely shares a common ancestor with cyanobacteria, the group containing the endosymbiont ancestor to the chloroplasts of modern plants, hence, Chlamydia retains unusual plant-like traits, both genetically and physiologically. In particular, the enzyme L,L-diaminopimelate aminotransferase, which is related to lysine production in plants, is also linked with the construction of chlamydia's cell wall. The genetic encoding for the enzymes is remarkably similar in plants, cyanobacteria, and Chlamydia, demonstrating a close common ancestry. This unexpected discovery may help scientists develop new treatment avenues: if scientists could find a safe and effective inhibitor of L,L-diaminopimelate aminotransferase, they might have a highly effective and extremely specific new antibiotic against chlamydia.
- "www.chlamydiae.com (professional) - Taxonomy diagram". Retrieved 2007-10-27.
- Chlamydia fact sheet from the Centers for Disease Control and Prevention
- Thylefors B, Négrel AD, Pararajasegaram R, Dadzie KY (1995). "Global data on blindness". Bull World Health Organ 73 (1): 115–21.
- Resnikoff S, Pascolini D, Etya'ale D, Kocur I, Pararajasegaram R, Pokharel GP, Mariotti SP (2004). "Global data on visual impairment in the year 2002". Bull World Health Organ 82 (11): 844–851.
- Belland R, Ojcius DM, Byrne GI (2004). "Chlamydia". Nat Rev Microbiol 2 (7): 530–1.
- NHS Chlamydia page
- Wagenlehner FM, Naber KG, Weidner W (2006). "Chlamydial infections and prostatitis in men". BJU Int. 97 (4): 687–90.
- Mabey DC, Solomon AW, Foster A (2003). "Trachoma". Lancet 362 (9379): 223–9.
- World Health Organisation. Trachoma. Accessed March 17, 2008.
- Ngondi J, Onsarigo A, Matthews F, Reacher M, Brayne C, Baba S, Solomon AW, Zingeser J, Emerson PM (2006). "Effect of 3 years of SAFE (surgery, antibiotics, facial cleanliness, and environmental change) strategy for trachoma control in southern Sudan: a cross-sectional study". Lancet 368 (9535): 589–95.
- Williams D, Churchill D (2006). "Ulcerative proctitis in men who have sex with men: an emerging outbreak". BMJ 332 (7533): 99–100.
- Leonhardt RM, Lee SJ, Kavathas PB, Cresswell P (2007). "Severe Tryptophan Starvation Blocks Onset of Conventional Persistence and Reduces Reactivation of Chlamydia trachomatis". Infect. Immun. 75 (11): 5105–17.
- Fairley CK, Gurrin L, Walker J, Hocking JS (2007). ""Doctor, How Long Has My Chlamydia Been There?" Answer:"... Years"". Sexually Transmitted Diseases 34 (9): 727–8.
- Mpiga P, Ravaoarinoro M (2006). "Chlamydia trachomatis persistence: an update". Microbiol. Res. 161 (1): 9–19.
- Meyers D, Wolff T, Gregory K. et al. USPSTF Recommendations for STI Screening" Am Fam Physician 2008;77(6) 819-824.
- U.S. Preventive Services Task Force (2007). "Screening for chlamydial infection: U.S. Preventive Services Task Force recommendation statement". Ann Intern Med 147 (2): 128–34.
- "National Chlamydia Screening Programme Data tables". Retrieved 2009-08-28.
- Gaydos CA et al (2004). Comparison of three nucleic acid amplification tests for detection of Chlamydia trachomatis in urine specimens. J Clin Microbio 42(7):3041-3045. doi:10.1128/JCM.42.7.3041-3045.2004
- Haugland S, Thune T, Fosse B, Wentzel-Larsen T, Hjelmevoll SO, Myrmel H (2010). "Comparing urine samples and cervical swabs for Chlamydia testing in a female population by means of Strand Displacement Assay (SDA)". BMC Womens Health 10: 9.
- al.], David N. Gilbert ... [et. The Sanford guide to antimicrobial therapy 2011. Sperryville, VA: Antimicrobial Therapy, Inc. p. 20.
- "Diagnosis and Treatment of Chlamydia trachomatis Infection - April 15, 2006 - American Family Physician". Retrieved 2010-10-30.
- Expedited Partner Therapy in the Management of Sexually Transmitted Diseases (2 February 2006) U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES PUBLIC HEALTH SERVICE. Centers for Disease Control and Prevention National Center for HIV, STD, and TB Prevention
- "WHO Disease and injury country estimates". World Health Organization. 2004. Retrieved Nov 11, 2009.
- Vos T, Flaxman AD, Naghavi M, Lozano R, Michaud C, Ezzati M, Shibuya K, Salomon JA, Abdalla S, et al. (Dec 15, 2012). "Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010.". Lancet 380 (9859): 2163–96.
- Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, Abraham J, Adair T, Aggarwal R, Ahn SY, et al. (Dec 15, 2012). "Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010.". Lancet 380 (9859): 2095–128.
- "STD Trends in the United States: 2010 National Data for Gonorrhea, Chlamydia, and Syphilis".
- Torrone, E; Papp, J; Weinstock, H (Sep 26, 2014). "Prevalence of Chlamydia trachomatis Genital Infection Among Persons Aged 14-39 Years - United States, 2007-2012.". MMWR. Morbidity and mortality weekly report 63 (38): 834–838.
- "Chlamydia". UK Health Protection Agency. Retrieved 31 August 2012.
- "STD Facts - Chlamydia". Retrieved 2007-10-26.
- McCoy AJ, Adams NE, Hudson AO, Gilvarg C, Leustek T, Maurelli AT (2006). "L,L-diaminopimelate aminotransferase, a trans-kingdom enzyme shared by Chlamydia and plants for synthesis of diaminopimelate/lysine". Proc. Natl. Acad. Sci. U.S.A. 103 (47): 17909–14.
- Chlamydia Fact Sheet from the CDC
- Links to chlamydia pictures at University of Iowa
- The National Chlamydia Screening Programme – The NCSP's official website containing information.
- Freetest.me – Free postal testing service operating across England.