Chlamydia trachomatis is a gram-negative, obligate intracellular bacterial pathogen. Chlamydia is the most common bacterial sexually transmitted disease (STD) and is especially common among people 15 to 25 years of age. Even though symptoms of Chlamydia are usually mild or absent, serious complications that cause irreversible damage, including infertility, can occur silently before a woman ever recognizes a problem. Symptoms, if present, may include bleeding between menstrual periods and after sexual intercourse, abdominal pain, painful intercourse, and an abnormal vaginal discharge. For men, symptoms include pus or milky discharge from the penis and inflammation of the prostate (prostatitis), or of the rectal area (proctitis). Maternal transmission of Chlamydia trachomatis causes neonatal conjunctivitis and pneumonia. It is important for those who are at increased risk of infection to have screening tests performed on a regular basis to check for possible exposure, especially since re-infection is common. The presence of specific IgA antibodies indicates current infection and is superior to using IgM specific antibodies as an indicator of acute or current infection.