Figure 1. Flowchart of aircraft passengers exposed to index case-patient 1 in investigation of 2 imported US cases of Middle East respiratory syndrome, by location at time of notification, May 2014. Of all passengers, 78 (88%) were on the London–Chicago flight, 9 (10%) on the Riyadh–London flight, and 2 (2%) on the Riyadh–London and London–Chicago flights. Domestic passengers were assigned to state health departments for follow-up if contact information indicated they lived in that state; CDC assumed responsibility for interviewing passengers if they lacked contact information that would enable state health department assignment. One US citizen was interviewed by CDC while traveling abroad; 1 US citizen with dual citizenship on the Riyadh–London flight was notified by CDC but already had been interviewed by authorities in the country of residence. FPHA notifications were made for foreign passport holders and US citizens living or traveling abroad. The incubation period for MERS is 2–14 days after exposure. Symptoms compatible with MERS were fever (>38°C [>100.4°F]), feverishness, symptoms of acute respiratory illness (i.e., cough, shortness of breath, rhinorrhea, sore throat), myalgia, malaise or gastrointestinal symptoms 2–14 days after travel on the same conveyance as the index case-patient. CDC, Centers for Disease Control and Prevention; FPHA, foreign public health authority; MERS, Middle East respiratory syndrome; MERS-CoV, MERS coronavirus.