The parents of a two-year-old Myanmar girl found infected with coronavirus disease after returning home from Thailand had worked in Ayutthaya and Nakhon Ratchasima provinces.
Disease control measures were already underway among people they had been in contact with, director-general of the Department of Disease Control, said on Thursday.
Provincial health officials had reported that the girl's parents had worked for a concrete block company in Pak Chong district of Nakhon Ratchasima from October last year, he said.
They had been registered as migrant workers in the northeastern province and had checkups at Pakchongnana Hospital before buying health insurance for migrants.
According to their Myanmar colleagues, the couple resigned from the company on June 25, and travelled by van to Ayutthaya for work on Aug 26.
Local health officials learned that they had applied for work at a market in Uthai district.
The Department of Disease Control and officials were implementing proper disease control measures, Dr Suwannachai said.
The mother and child returned to Myanmar through Mae Sot district, Tak, on Sept 4. Her infection was confirmed by a test in Myanmar on Sunday. A night curfew has been imposed in Myawaddy town, opposite Mae Sot.
It is believed they used one of about 50 uncontrolled natural border crossings, avoiding efforts to tighten controls to stop illegal migrants and prevent the spread of Covid-19.
As part of measures to contain the disease, health officials collected samples from 2,635 Thais and foreigners in Mae Sot on Sept 8-9 for testing. None were positive for Covid-19.