Chlamydia infection ( from the Greek , Ï Î '' Î Î 1\/4 Ï Î Î Ï meaning `` cloak '' ) is a common sexually transmitted infection ( STI ) in humans . It is caused by the bacterium Chlamydia trachomatis . Chlamydia infection ( from the Greek , Ï Î '' Î Î 1\/4 Ï Î Î meaning `` cloak '' ) is a common sexually transmitted infection ( STI ) in humans caused by the bacterium Chlamydia trachomatis .