On May 1, 2014, the first U.S. imported case of Middle East Respiratory Syndrome (MERS) was confirmed in a traveler from Saudi Arabia and United Arab Emirates (UAE) to the U.S. On May 11, 2014, a second U.S. imported case of MERS was confirmed in a traveler who also came from Saudi Arabia. The two U.S. cases were not linked.

The first case of MERS in the United States, identified in a traveler recently returned from Saudi Arabia, was reported to CDC by the Indiana State Department of Health on May 1, 2014, and confirmed by the CDC. On May 16, 2014, an Illinois resident who had contact with the first case of MERS in the U.S. tested positive for MERS-CoV.

The Middle East respiratory syndrome coronavirus (MERS-CoV) was first reported in September 2012 in a Saudi Arabian patient with pneumonia. As of 12 May 2014, MERS-CoV had been confirmed by the World Health Organization (WHO) in 536 patients; all cases were related to residence, recent travel, or contact with a recent traveler from the Arabian Peninsula. Initial reports of clinical course among MERS-CoV case patients from Saudi Arabia revealed high case fatality proportions, but subsequent increases in testing of symptomatic and asymptomatic persons as part of contact investigations has revealed that approximately one-fifth to one-quarter of cases are mildly symptomatic or asymptomatic. As of April 2014, travel-associated cases have been detected in 8 countries outside the Arabian Peninsula.