Chlamydia is the most frequently reported bacterial sexually transmitted infection in the United States. In 2011, 1,412,791 cases of chlamydia were reported to CDC from 50 states and the District of Columbia, but an estimated 2.8 million infections occur annually. A large number of cases are not reported because most people with chlamydia do not have symptoms and do not seek testing. Chlamydia is most common among young people. It is estimated that 1 in 15 sexually active females aged 14-19 years has chlamydia.
Chlamydia conjunctivitis or trachoma is a common cause of blindness worldwide. The World Health Organization estimates that it accounted for 15% of blindness cases in 1995, but only 3.6% in 2002.
Chlamydia causes more than 250,000 cases of epididymitis in the U.S. each year. Chlamydia causes 250,000 to 500,000 cases of PID every year in the United States. Women infected with chlamydia are up to five times more likely to become infected with HIV, if exposed.