A Pathum Thani market was infected with Covid-19 from Samut Sakhon and has spread the disease to other provinces, according to a government spokeswoman.
Apisamai Srirangson, of the Centre for Covid-19 Situation Administration, said on Monday that Covid-19 cases linked to Samut Sakhon were first confirmed in Pathum Thani on Dec 22.
The carriers were mobile food vendors who had visited a seafood market in Samut Sakhon.
From Jan 4 to 13, disease control workers tested 3,432 people at Pornpat market in Thanyaburi district of Pathum Thani, part of outer northern Bangkok, and 45 of them, or 1.31%, tested positive for Covid-19, Dr Apisamai said.
The market had been closed but reopened on Jan 16.
On Jan 30, a Myanmar woman selling vegetables at the market had reported losing her sense of smell and taste. She tested positive for Covid-19 on Feb 7.
Active case finding then began, with 1,333 people at the market tested from Feb 9 to 13, and 175 of them were positive. This time the infection rate rose to 13.13% of tested people, Dr Apisamai said.
Pornpat market is not enclosed. It has a low roof and ventilation is poor. Vendors tend to remove their face masks when it is hot, the spokeswoman said.
The market was on Friday ordered closed for five days, and is due to reopen on Wednesday. Health officials advise people who visited the market from Feb 9-13 to observe their health closely and visit a doctor or hospital if they notice any symptoms of Covid-19.
Dr Apisamai said many new Covid-19 cases had been linked to the market. They included 164 in Pathum Thani, seven in Nakhon Nayok, three in Phetchaburi, two each in Saraburi and Bangkok and one each in Ayutthaya, Ang Thong, Nakhon Ratchasima and Phrae.
On Sunday, Pathum Thani province reported 50 new Covid-19 infections, all found through active testing in communities - 37 Thais, eight Myanmar and five Lao people.