Particles of the Middle East respiratory syndrome (MERS) coronavirus that emerged in 2012 are seen in an undated colorized transmission electron micrograph from the National Institute for Allergy and Infectious Diseases (NIAID).
Particles of the Middle East respiratory syndrome (MERS) coronavirus that emerged in 2012 are seen in an undated colorized transmission electron micrograph from the National Institute for Allergy and Infectious Diseases (NIAID). REUTERS/National Institute for Allergy and Infectious Diseases/Handout via Reuters REUTERS/National Institute for

The U.S.' Centers for Disease Control has reneged on its earlier observations that the Illinois man believed to have been the country's third MERS-CoV case contracted the disease from human-to-human transmission from the Indiana man. The latter is the U.S.' second confirmed case.

The CDC conducted a series of more thorough and extensive blood tests on the Illinois man to check if his infection was indeed the first human-to-human transmission MERS case in the U.S.

However, the "CDC has concluded that the Illinois resident was not previously infected with MERS-CoV," according to the agency.

"The initial ELISA and IFA serology results indicated the possibility that the Illinois resident had been previously infected with MERS-CoV," David Swerdlow, MD, who is leading CDC's MERS-CoV response, said. "This compelled us to notify and test those people with whom he had close contact in the days following his interaction with the Indiana MERS patient."

The Illinois resident had a face-to-face encounter with the Indiana MERS patient in a business meeting.

"While we never want to cause undue concern among those who have had contact with a MERS patient, it is our job to move quickly when there is a potential public health threat," Swerdlow said in. "Because there is still much we don't know about this virus, we will continue to err on the side of caution when responding to and investigating cases of MERS in this country."

The first two confirmed MERS-CoV cases in the U.S. came from Indiana and Florida. Both patients were health care providers in Saudi Arabia who had imported the disease in the country.

Meantime, Iran reported its first death from the MERS-CoV on Thursday.

According to the IRNA news agency, the country's official news outlet, the victim was a 53-year old woman. Her two sisters had also contracted the virus.