The genus Chlamydia includes three species: Chlamydia trachomatis, the recently described Chlamydia pneumoniae, primarily associated with humans, and Chlamydia psittasi, primarily associated with animals. Chlamydia trachomatis comprises 15 known serovars, is associated with trachomatis and gentourinary infection, and three serovars are associated with lymphogranuloma venereum (LGV). Chlamydia trachomatis infections are the most common bacterial sexually transmitted diseases. Approximately 4 million new cases occur each year in the United States, primarily cervicitis and nongonococcal urethritis. This organism also causes conjunctivitis and infant pneumonia. Chlamydia trachomatis infection has both a high prevalence and asymptomatic carriage rate, with frequent serious complications in both women and neonates. Complications of chlamydia infection in women include cervictis, urethritis, endometritis, pelvic inflammatory diseases (PID) and increased incidence of ectopic pregnancy and infertility. Vertical transmission of the disease during parturition from mother to neonate can result in inclusion conjunctivitis and pneumonia. In men, at least 40% of cases of nongonococcal urethritis are associated with chlamydia infection and epididymitis. Approximately 70% of women with endocervical infections and up to 50% of men with urethral infections are symptomatic.
Chlamydia psittasi infection is associated with respiratory disease in individuals exposed to infected birds and is not transmitted from human to human. Chlamydia pneumonia, first isolated in 1983, is associated with respiratory infections and pneumonia. Traditionally, chlamydia infection has been diagnosed by the detection of chlamydia inclusions in tissue culture cells. Culture method is the most sensitive and specific laboratory method, but it is labour intensive, expensive, lengthy (2-3 days) and not routinely available in most institutions. Direct tests such as immunofluorescence assay (IFA) require specialized equipment and a skilled operator to read the result.