In December 2008, an outbreak of contagious equine metritis (CEM) was reported in Kentucky. The index case was a healthy stallion that underwent routine testing for exportation of semen and the causative agent, Taylorella equigenitalis, was isolated by cutlure on December 15. By the end of the month, three more stallions on the same farm were also identified as infected. At the moment, it is estimated that there are 28 horses in Kentucky and another 156 horses outside Kentucky that have been exposed. Another 250 horses are being traced across 27 states. The last outbreak of CEM in the USA was in 1979 in Missouri, although a few sporadic cases have been identified in the country in the last three decades. It is a reportable disease in both the USA and Canada, and there are strict import (and export) regulations for horses entering the USA and Canada from CEM-positive countries.

From the USDA Newsroom:
http://www.aphis.usda.gov/newsroom/hot_issues/cem/index.shtml

Please note the ISU VDL does not test for CEM, below is a link of approved labs that do the testing:
http://www.aphis.usda.gov/animal_health/lab_info_services/downloads/ApprovedLabs_CEM.pdf