The man fell ill after flying to the US late last week from Saudi Arabia where he was a health care worker.
He is hospitalised in good condition in northwest Indiana with Middle East respiratory syndrome, or MERS, the Centres for Disease Control and Prevention and Indiana health officials said yesterday.
The virus is not highly contagious and this case "represents a very low risk to the broader, general public," Dr Anne Schuchat told reporters during a CDC briefing.
So far, it is not known how he was infected, Schuchat said.
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Saudi Arabia has been at the centre of a Middle East outbreak of MERS that began two years ago. The virus has spread among health care workers, most notably at four facilities in that country last spring.
Officials didn't provide details about the American's job in Saudi Arabia or whether he treated MERS patients. Overall, at least 400 people have had the respiratory illness, and more than 100 people have died. All had ties to the Middle East region or to people who travelled there.
"Given the interconnectedness of our world, there's no such thing as 'it stays over there and it can't come here,'" said Dr W Ian Lipkin, a Columbia University MERS expert.
MERS belongs to the coronavirus family that includes the common cold and SARS, or severe acute respiratory syndrome, which caused some 800 deaths globally in 2003.