Health officials backtracked an earlier report that first case of Middle East respiratory syndrome had spread to the US

Health officials on Wednesday backtracked on an earlier report that a mysterious Middle East virus had apparently spread from one person to another in the United States.

Additional testing has shown the virus did not, in fact, spread to an Illinois man from a traveler he'd met in a business meeting.

The Centers for Disease Control and Prevention announced the revised diagnosis on Wednesday.

This month, a doctor who traveled from Saudi Arabia to Indiana was identified as the first US case of Middle East respiratory syndrome, or Mers. Officials tested people he met, and two preliminary tests detected antibodies against Mers in the Illinois man.

No other contacts tested positive.

On 17 May, CDC officials called a news conference to announce the test results. They said the Illinois man was not sick and tests for presence of the actual virus in him had been negative, but the blood tests that detected antibodies to the virus were sufficient grounds to take action. Health officials began testing people he had been in contact with and asked the man to wear a mask and avoid crowds.

Since then, other tests – including a more definitive one that takes five days to complete – have discounted that finding, CDC officials said Wednesday.

Asked if they had jumped the gun with the earlier announcement, one official said the CDC will continue to err on the side of caution if it might stop potential spread of a dangerous new disease. "We can't wait until we have all the tests back in order to take public health action," said Dr David Swerdlow, who is managing the CDC's response to the recent Mers reports.

It's not clear what caused the earlier false positive test results. It's possible the tests reacted to the antigen for a virus with similarities to Mers, officials said.

Health officials were relieved to get the new results. They had believed the virus must have spread from the Indiana man to the Illinois man during a business meeting that involved no closer contact than a handshake. That suggested it might spread a little easier than some had thought – in the Middle East, the virus has spread more intimately, to family members or health care workers caring for a Mers patient.

CDC officials said they still think it's possible the virus can spread in an extended, face-to-face business meeting. But "it is a little reassuring that this gentleman is not a case," Swerdlow said.

Mers has sickened more than 600, mostly, in the Middle East, and killed more than 175. The Mers germ belongs to the coronavirus family that includes the common cold and Sars, which caused some 800 deaths in 2003.