South Korean health officials confirmed the country's third case of Middle East Respiratory Syndrome (MERS) Thursday, with the two latest cases found in people who had been in contact with the first patient after he returned from the Middle East, Yonhap reported.

Authorities have also isolated as a precaution another 64 people who are family members or medical workers treating those three patients, said Yang Byung-guk, director of the health ministry's Korea Centers for Disease Control & Prevention.

Test results came back positive for a 63-year-old woman, the wife of the first proven case, as well as for a 76-year-old man who shared a hospital room with him, the health ministry said.

The first man was diagnosed with the disease Wednesday after a trip to Bahrain, Saudi Arabia and the United Arab Emirates, where the disease broke out, Yang told a briefing.

Shin Hyoung-shik, an infectious disease specialist in charge of treating the patients, said the latest two confirmed cases had fevers but no sign of breathing difficulties.

"The first patient has been recovering, with less difficulty in breathing," Shin said.

The ministry said on Wednesday it saw no chance of the disease spreading into the wider population because those who had been in contact with the first patient had been isolated.

The disease's fatality rate is 30-40 percent and its incubation period is two to 14 days, experts say.

"The 40 percent death rate is quite high. If infected, patients in many cases need to have artificial respiration treatments for respiratory failures," Choi Jun-yong, an associate professor at the infectious diseases division of Severance Hospital, told Reuters by phone.

First identified in humans in 2012, MERS is caused by a coronavirus, from the same family as the one that caused a deadly outbreak of Severe Acute Respiratory Syndrome (SARS) in China in 2003. There is no cure or vaccine.

The World Health Organization has had reports of 1,118 cases, including 423 deaths. There is usually a surge of cases in the northern spring and most cases have come from hospital transmission.