The South African Covid-19 variant believed to be resistant to vaccines was detected in a Thai returnee from Tanzania late last month, according to director-general of the Department of Disease Control, Opas Karnkawinpong.
"The department is closely monitoring the situation following concerns the South African variant may have reached Thailand," he told the media in press briefing on Sunday.
The infected patient is a 41-year-old Thai man who had travelled to Tanzania for business before returning to Thailand on Jan 29. He tested positive while staying in state quarantine and is currently in hospital.
Dr Opas insisted there is no evidence in the case of this patient that the mutated variant had led to more severe disease.
"Mutations, such as the G variant from England, may make the virus spread faster but they are less severe," he said.
As of now, there is only a preliminary study suggesting the Covid-19 vaccine provided limited protection against the South African variant, Dr Opas said.
In the wider context of the outbreak, the Ministry of Public Health is now focusing on Pathum Thani province, in addition to Samut Sakhon, after a cluster of new cases was detected at the Pornpat fresh market in Thanyaburi district last week, prompting a temporarily closure order and widespread testing, Dr Opas said.
He said infections had soared at the Pornpat fresh market because a number of cases was among infected vendors who operated stalls at the centre of the seafood hub.
There were 1,333 people tested and 175, more than 10%, came back positive. Some 111 of the infected were Thai and the rest were migrant workers, he said.
The market now has a total of 182 confirmed cases, including people who had travelled there from from eight provinces -- Nakhon Nayok, Phetchaburi, Saraburi, Bangkok, Ayutthaya, Ang Thong, Nakhon Ratchasima, and Phrae.
Disease investigators have speculated the contagion was exacerbated by the market's low ceiling and bad ventilation, the doctor said.
"Some of the vendors sold products at various markets in different provinces, causing the virus to spread to other areas fast," he said.
Nakhon Ratchasima provincial public health chief, Narinrat Pitchayakhamin said the latest case in the province was a seven-year-old boy from Pathum Thani.
The boy travelled to Nakhon Ratchasima with his family on Feb 10 to attend a cremation ceremony and was later found to have contracted the virus.
District chief Sanit Sritawee said health officials are tracking 14 people who were in close contact with the patient during the cremation ceremony in the village.
Nakhon Ratchasima has recorded 11 more cases since the return of Covid-19 to the country.
Nine have recovered and two are still being treated at Maharat Nakhon Ratchasima Hospital, where the new patient was also admitted.
Nakhon Pathom, another province with a rise in cases, reported eight new positive tests on Sunday, bringing the its overall tally to 88, 85 of whom are Thai. All of the new cases are relatives of the previous case, including a 68-year old man living in the same house in tambon Don Faek in Nakhon Chai Si district.
In Samut Sakhon, provincial public health officers sanitised all 22 markets in the municipality over the weekend and all of them, except Rot Fai market, will reopen today.
The Central Shrimp Market in which the first cluster of new cases was blamed for the re-emergence of the virus in Thailand is to remain shut for the time being.
Meanwhile, Thailand on Sunday reported 166 new coronavirus cases, almost half of them from mass testing in Pathum Thani and Samut Sakhon.