STI | Chlamydia

Chlamydia is the most common sexually transmitted disease in the world. If left untreated, chlamydia can lead to infertility and increase the risk of ectopic pregnancy.

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Chlamydia is a genus of Gram-negative bacterial species that encompasses two pathogens that are commonly associated with infecting humans, C. pneumonia  and C. trachomatis. C. pneumonia is a common cause of atypical pneumonia, whereas C. trachomatis is the pathogen that causes the sexually transmitted disease of chlamydia.


Chlamydia is the most common sexually transmitted infection in the world. According to the World Health Organization, there were an estimated 374 million new sexually transmitted infections in 2020, of which 129 million were classified as chlamydia. Sexually active individuals and individuals with multiple partners are at highest risk. In men, C. trachomatis  infection can lead to inflammation of the urethra, also referred to as urethritis. C. trachomatis  infections in women may lead to inflammation of the cervix. An untreated infection may spread to the uterus or the fallopian tubes, causing salpingitis or pelvic inflammatory disease. These conditions can lead to infertility and increase the risk of ectopic pregnancy. 

C. trachomatis  bacteria are transmitted by having vaginal, anal or oral sex with someone who is infected. Infection of a pregnant woman may spread to the uterus after delivery (late postpartum endometritis). In addition, the infant may develop C. trachomatis -related conjunctivitis (eye infection) and pneumonia.

There is no vaccine to prevent chlamydia. However, sexually active people can follow preventative steps to reduce the risk of acquiring C. trachomatis, including:

  • Proper use of latex condoms for males and polyurethane dental dams for females

  • Limiting the number of sex partners

  • Regular screening for chlamydia

A mutually monogamous sexual relationship with an uninfected partner or abstinence are the most effective ways to avoid infection.

Many people with chlamydia have no symptoms, especially in the early stages of the infection, which is why it is recommended for sexually active people to be screened. Females with symptoms of chlamydia may experience:

  • Vaginal discharge

  • Vaginal itching

  • Vaginal bleeding when not menstruating

  • Painful sexual intercourse

Men with chlamydia may experience discharge from the penis or swelling and pain in the testicles. For those with chlamydia symptoms, it is advised to seek a diagnosis.

The diagnosis of a C. trachomatis infection involves sampling of the urethral discharge in males or cervical secretions in females. If an individual engages in anal sexual contact, samples from the rectum may also be required for testing. Traditionally, samples have been tested utilizing fluorescent or monoclonal antibody tests, DNA probe tests, or cell culture methods. Nucleic acid amplification tests, such as polymerase chain reaction and transcription mediated amplification, are now routinely used to identify C. trachomatis.

Standard treatment for chlamydia is the administration of antibiotics, including:

  • Tetracyclines

  • Azithromycin

  • Erythromycin 

Co-infection with gonorrhea or syphilis is common, so patients with signs and symptoms of a sexually transmitted infection should be screened for other sexually transmitted diseases as well. Upon a positive result, all sexual partners should be notified to also be screened for chlamydia. All sexual partners must be treated individually to prevent the transmission, and re-transmission, of the infection. There is no significant immunity following an infection, and individuals may repeatedly contract the disease. A follow-up evaluation may be done four weeks after treatment to determine if the infection has been resolved.