Dr Yongyos Thammawut, deputy permanent secretary for health, said one was a 41-year-old woman who had not travelled abroad but was in close contact with a previously recorded COVID-19 patient, a man who returned from Italy.
She developed a fever on Saturday (Mar 7), was examined and then registered as the 51st local case. She was being treated at Rajavithi Hospital in Bangkok.
The 52nd and 53rd cases are a couple. The wife, 46, returned from Italy to Thailand on Feb 28 and later did not feel well. Her husband, 47, did not go abroad and fell sick on Saturday with a high fever and body ache.
The man went to a hospital first and tested positive for the disease. His wife was then tested. Both had been in voluntary home quarantine. They were now receiving treatment at a hospital in Nakhon Pathom province.
The three confirmed infections raised the number of local cases to 53. Of these, 33 had recovered and returned home, 19 were at hospitals and one died. One of the hospitalised patients was critically ill at the Bamrasnaradura Infectious Diseases Institute in Nonthaburi province.
Patients under investigation numbered 4,682 and 61% of them had recovered. Most had seasonal influenza, Dr Yongyos said.
Meanwhile, Sattahip naval base in Chon Buri province has already received for quarantine 188 Thais who returned from working illegally in South Korea - 88 men and 100 women. Eight of them came back from Daegu and North Gyeongsang province, the centre of the outbreak in South Korea.
Special care was being given to 20 people at Sattahip - five pregnant women, four young children and 11 people with chronic diseases, Dr Yongyos said.