South Korean health officials confirmed the country's third case of Middle East Respiratory Syndrome (MERS) on 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.
Authorities have 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 Centres 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 ministry said.
The first man was diagnosed with the disease on 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 per cent and its incubation period is two to 14 days, experts say.
"The 40 per cent death rate is quite high," Choi Jun-yong, an associate professor at the infectious diseases division of Severance Hospital, told Reuters by telephone.
"If infected, patients in many cases need to have artificial respiration treatments for respiratory failures."
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 in China in 2003. There is no cure or vaccine.
South Korea's health ministry said 23 countries had a combined 1,142 cases of MERS and 465 deaths had been reported, as of May 16. Of the total, 1,117 cases, or 97.8 per cent, were in the Middle East.
There is usually a surge of cases in the northern spring and most cases have come from hospital transmission.