Chlamydia infection is a common sexually transmitted infection in humans caused by the bacterium Chlamydia trachomatis. The term Chlamydia infection can also refer to infection caused by any species belonging to the bacterial family Chlamydiaceae. Chlamydia trachomatis is found only in humans. It is a major infectious cause of human genital like Pelvic inflammatory disease and eye disease, the World Health Organization estimates that it accounted for 15% of blindness cases in 1995, but it reduced to 3.6% in 2002.