An American Airlines Group Inc. pilot tested positive for coronavirus, becoming the first at the carrier to be diagnosed with the disease that’s infected more than 128,000 people globally and killed nearly 5,000.

The aviator is undergoing treatment, American’s pilots union said today. Neither the Allied Pilots Association nor the airline would confirm when the pilot became ill, say if he or she was flying recently or release any personal information.

The union learned of the coronavirus case Wednesday night. American said in a statement it is “in close contact” with the Centers for Disease Control and Prevention and public health officials.

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Airlines are reeling from the pandemic, which has spurred mass cancellations by worried passengers and prompted U.S. President Donald Trump to restrict trips from Europe to the U.S. The limits, effective Friday, are to last at least 30 days. The American case may be just the start of crew members falling ill, said Robert Mann, an aviation consultant.

“I’d be shocked if it didn’t occur more and more frequently as things go on,” said Mann, president of R.W. Mann & Co. “I’d say the same of flight attendants. The real concern is that crew members have a strong motivation — sometimes it’s financial and sometimes it’s fear of repercussions — to fly when they’re ill and they may think it’s a mild cold.”

Mann said he would still be more concerned about exposure to fellow passengers who may be ill than crew members.

The American Airlines pilot, who is based in Dallas-Fort Worth, may be among the first in the industry to be diagnosed with the virus. American has about 15,000 pilots.

A Standard & Poor’s index of major U.S. carriers tumbled 20% at the close in New York today, the worst since the immediate aftermath of the terrorist attacks on Sept. 11, 2001. American fell 17% to $13.45, a record drop.