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.