The case involved a 39-year-old Indonesian domestic helper who arrived in Hong Kong in February.
She lived with her employer’s family at Earl Gardens in Kowloon Tong from April 6 to May 19.
The helper then moved out and lived in a Yau Ma Tei flat provided by her agency with several other domestic helpers.
Officials said the patient also twice visited Immigration Headquarters in Wanchai this month.
Authorities said the woman was planning to return to Indonesia on Sunday, but a compulsory Covid-19 test she did on Friday found her to be infected.
A test she took on May 4 under an earlier testing order came back negative.
Meanwhile, there was one imported case involving a 20 year-old man who flew in from the US and started showing symptoms on Friday.
Officials said he wasn’t found to carry any mutated virus.