A healthcare worker (age, gender, nationality, and profession unknown) flew on April 24 from Riyadh to London and then on to Chicago, Illinois. (When I think about the swarms changing planes and going through security at Heathrow, I wince.)
From Chicago the patient took a bus to somewhere in Indiana, and felt respiratory problems. On April 28 the patient entered an emergency department and was admitted the same day. A test for MERS was evidently done pretty quickly (unsurprising, given the patient's recent whereabouts, which he or she would have told the Indiana people about at once). The test confirmed MERS this afternoon, presumably in the last two or three hours.
However, CDC has been doing some kind of investigation (contact tracing) in the past 24 hours, which makes sense. Communication has doubtless been intense among CDC, WHO, ECDC, PHE, and the Saudi Ministry of Health.
This case is very interesting, but not very surprising or very threatening. MERS is likely to get a very cold welcome in the US. The main consequences are likely to be more careful screening of outbound passengers from the KSA, and again in airports receiving Saudi-origin flights. The chief outcome of this case is likely to be to lend yet another disagreeable aspect to modern air travel.