The 75-year-old patient tested positive for the Middle East Respiratory Syndrome on Thursday.
Authorities are ensuring the situation remains under control, with a total of 141 people in the country on the watch-list. Most of these people had already been located and quarantined, said Dr Rajata Rajatanavin, Public Health Minister.
Health authorities are working with other agencies such as the Foreign Ministry, the Disaster Prevention and Mitigation Department and the Bangkok Metropolitan Administration to prevent the spread of MERS.
"There are two groups of people who had close contact with the MERS patient. The first group of 66 people, including three close relatives, 47 medical staff and airline passengers who sat close to the patient on the plane on their way to Thailand are at greater risk," Rajatanavin said.
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"The second group has 75 people which came close to the patient but did not have direct contact. They were other airline passengers, taxi drivers and hotel staff. All of them will be monitored for 14 days but they don't need to go to hospital yet," the minister added.
Rajatanavin also said the condition of the MERS patient, a 75-year-old man from Oman, had improved slightly but he was still in a special unit at Bamrasnaradura Infectious Diseases Institute in Nonthaburi.
Three of his close relatives had been isolated in the same unit as well, two of them have flu symptoms.
Meanwhile, Tourism Council of Thailand president Ittirit Kinglake said MERS could trigger fear among Thais as well as tourists staying in the country. However, he said people should not panic.