Updated

Two U.S. hospital workers who fell ill after contact with a patient suffering from Middle East Respiratory Syndrome (MERS) have tested negative for the often-deadly virus, a Florida health official said on Wednesday.

U.S. health officials had recently confirmed the country's first two cases of MERS since late April, raising fears about the global spread of the virus responsible for a worsening outbreak in Saudi Arabia. More than 500 cases have been reported worldwide, with about 30 percent proving fatal.

The World Health Organization said Wednesday while its concern over MERS had significantly increased, the disease does not yet pose a global health emergency.

The second confirmed case of MERS on U.S. soil was hospitalized in Orlando, Florida after a 12-hour stay in the emergency department, potentially exposing healthcare workers to the virus.

Florida officials said they were monitoring a total of 20 healthcare workers who had been in contact with the patient. Test results of those workers have also so far proved negative for MERS, according to Kevin Sherin, director of the Florida Department of Health in Orange County. He could not specify the number of test results received.

Scientists have few details on how the MERS virus spreads, but healthcare workers have proven particularly vulnerable due to their close contact with infected patients. Both U.S. cases involved healthcare workers who had spent time in Saudi hospitals that are treating people with MERS.