The chief master sergeant initially tested positive for MERS on Wednesday. Because he showed no symptoms of the illness, he received further testing which reconfirmed that he has MERS.
The sergeant had received treatment for his Achilles heel at the same hospital as the first MERS patient in Korea, who became sick after visiting four Middle Eastern countries.
There are no other diagnosed cases of MERS on base, according to a statement released by Osan Air Base on Thursday. But six civilians and 64 soldiers -- all Koreans -- remain under quarantine in their barracks to prevent further infection on the base.
The Osan Air Base, located south of the capital Seoul, was built by the United States during the Korean War.
MERS doesn't transmit easily
MERS does not easily spread between humans. But concerns over the spread of the Middle East Respiratory Syndrome has prompted the closure of more than 1,000 schools.
The syndrome, which surfaced only three years ago, is not well understood. Because the virus is still fairly new, doctors and scientists do not know the exact source or mode of MERS transmission.
The South Korean outbreak, which had its first case on May 20, involved 64 confirmed cases and five deaths as of Saturday evening, the country's health ministry said. The vast majority of the cases are hospital clusters and the deaths were among people with pre-existing health conditions.
Experts from the World Health Organization who have dealt with MERS are coming to South Korea to assess the pattern of the virus spread and to look at public health response efforts.
The outbreak in South Korea has been the largest outside of Saudi Arabia -- where the virus was discovered.
Seoul on alert
South Korea's capital on Thursday began asking more than 1,500 people to self-quarantine because they unknowingly attended a symposium with a doctor who was infected with MERS, Seoul's mayor said.
MERS spreads from close contact with an ill person, such as living with or caring for them, according to the U.S. Centers for Disease Control and Prevention
But Seoul Mayor Park Won-soon said all 1,565 people who attended the symposium should stay at home as a precaution, to avoid spreading the disease in the unlikely event that they contracted MERS at the meeting.
The mayor said the city is considering measures that would force these people to stay at home, and that officials are trying to determine where else the doctor traveled while he had symptoms.
Kang Shin-myun, Seoul chief of police, said it will enforce quarantine orders for those suspected of having MERS.
"We will deal strongly with anyone who escalates unnecessary sense of public uneasiness," he said in a media release.
Criticisms on communication
The mayor also criticized the lack of communication from national health officials regarding MERS during his Thursday press conference.
The national government responded to criticisms. "We are concerned that the mayor's statement at a press conference last night may escalate sense of uneasiness among the public," an official from the Blue House, the South Korean president's office said.
The national government has been viewed with suspicion -- especially after what many perceive as its bungled response to the sinking of the Sewol ferry last year. And the government's withholding of the names of the hospitals affected by MERS fueled further suspicion.
As of June 3, 1,179 cases of MERS have been confirmed in 25 countries, according to the World Health Organization. Two of those cases were in the United States -- both were health workers who lived in Saudi Arabia.