Chlamydia includes three species: Chlamydia trachomatis, Chlamydia pneumonia and Chlamydia psittasi.

Chlamydia trachomatis, a human pathogen, is subdivided into 15 known serovars; 3 are associated with Lymphogranuloma Venereum and the remaining 12 with trachomatis and genitourinary infection. Common complications of women infected with Chlamydia include cercicitis, urethritis, endometritis, pelvic inflammatory disease and increased incidence of ectopic pregnancy and infertility, and of men include urethritis and epididymitis. Chlamydia trachomatis infection has a high prevalence and asympomatic carriage rate. Approximately 70% of women with endocervical infections and up to 50% of men with urethral infections are asymptomatic. Chlamydia psittasi, mainly an animal pathogen, is associated with respiratory disease caused by exposure to infected birds and not transmitted through human interaction.

Chlamydia pneumonia, first isolated in 1983, is a human pathogen and is associated with respiratory infections and pneumonia.

Traditionally, Chlamydia infection is diagnosed by detection of Chlamydia inclusions in tissue culture cells. Although this method is the most sensitive and specific laboratory method, it is costly, labor intensive, time consuming (48-72 hours) and not routinely available in most institutions. Direct immunofluorescence assay requires specialized equipment and a skilled operator to interpret results. The One-Step Chlamydia Test, utilizing the gold particle based immunoassay, provides a simple, rapid, specific yet highly sensitive method of detection of Chlamydia antigen.