WEDNESDAY, May 14, 2014 (HealthDay News) -- The World Health Organization says that, while there's growing concern about infections caused by the MERS virus, the threat does not yet constitute a public health emergency.
That's because there's "no evidence of sustained human-to-human transmission" of the mysterious virus that first surfaced in the Middle East two years ago, the WHO said in a news release issued Tuesday.
The vast majority of MERS cases have been reported in Saudi Arabia, although there have been two confirmed reports of infection in the United States. Both cases involved health care workers who had worked in Saudi facilities caring for MERS patients before they traveled to the United States in recent weeks.
MERS has killed about one-quarter of the people who contracted the virus, U.S. health officials have reported.
On Wednesday, health officials reported that two Florida hospital workers who helped treat the man with the second diagnosed case of MERS in the United States had tested negative for the virus. They were tested to see if they may have caught the virus from the man, hospital officials said.
News of the second U.S. case of MERS was announced Monday by federal health officials.
Like the first U.S. case identified earlier this month, the second case involved a health care provider who lived and worked in Saudi Arabia, the epicenter of the MERS outbreak. The second patient -- an unidentified man -- was being treated at the Orlando hospital and was said to be doing well.
The health risk from MERS to the general public is very low, federal officials said Monday, because the virus is only passed through close contact.
The second U.S. patient worked in a facility in Saudi Arabia that cared for MERS patients. The patient was visiting family in central Florida before entering the hospital. The patient had traveled from Saudi Arabia to London to Boston to Atlanta, before reaching Florida, officials said.
The patient felt unwell on a May 1 flight to London, but sought care in Orlando. The U.S. Centers for Disease Control and Prevention said it had notified all passengers on the affected flights to be on the lookout for symptoms.
MERS symptoms typically include shortness of breath, coughing and fever.
However, Dr. Anne Schuchat, director of the U.S. National Center for Immunization and Respiratory Diseases, said Monday that it is "likely that if you have not already developed symptoms you are not likely to."
CDC Director Dr. Tom Frieden said his agency was contacting the airlines on which the patient traveled, but the risk to people traveling with a person infected with MERS is unknown.
As of Monday, there were 538 confirmed cases of MERS worldwide, and 145 deaths. The vast majority of cases and deaths -- 450 and 118, respectively -- have occurred in Saudi Arabia.
One-fifth of all MERS cases have occurred among health care workers, Schuchat said.
Frieden added, "We would not be surprised to see more cases, but we are not predicting there will be."
On April 28, another U.S. health care worker who'd had close contact with MERS patients in Saudi Arabia was admitted to an Indiana hospital and was later diagnosed with the respiratory ailment.
He was released from Community Hospital in Munster on Friday.
In some countries, the virus has spread from person to person through close contact, such as caring for or living with an infected person. But, there's currently no evidence of sustained spread of MERS in general settings, the CDC has said.
The first patient took a plane on April 24 from Riyadh, Saudi Arabia, to London, then from London to Chicago. He then took a bus from Chicago to Indiana. On April 27, he started experiencing "respiratory symptoms," and was admitted to Community Hospital the next day, the CDC said.
Camels have been identified as carriers of MERS, but it's not known how the virus is being spread to people.
For more on MERS, visit the World Health Organization.
SOURCES: May 13, 2014, news release, World Health Organization, Geneva, Switzerland; May 12, 2014, news conference, with Anne Schuchat, M.D., assistant surgeon general, United States Public Health Service, and director, U.S. National Center for Immunization and Respiratory Diseases, and Thomas Frieden, director, U.S. Centers for Disease Control and Prevention; May 2, 2014, news release, U.S. Centers for Disease Control and Prevention; NBC News