A 75-year-old woman confirmed with COVID-19 in Guangzhou, Guangdong province, on Friday had contracted a mutated strain that had come from India, medical experts found after clinical studies and gene sequencing.

The patient, surnamed Guo, might have been exposed accidentally, a statement released by Guangzhou's Liwan district said on Monday.

The woman's husband, surnamed Lu, was confirmed positive on Sunday afternoon. It was his third test after his wife's positive test, the statement said. Lu was sent to Guangzhou No Eight People's Hospital, which is designated for COVID-19 patients, for further observation and treatment, it said.

All close contacts of the couple have been quarantined for further medical observation.

Both Guo and Lu, who live in Liwan district's Longjin community, had been in Guangzhou for more than two weeks before they fell ill. They had not visited any areas of medium or high risk.

Guo took some flu medicine herself when she felt uncomfortable last Tuesday, and she had a fever the next day. She walked to a nearby clinic to seek medical help on Thursday afternoon.

Guo's test came back positive early on Friday morning. She had only developed mild symptoms. Lu's tests were negative in the first two examinations after Guo's infection was confirmed.

Disease prevention and control departments from the province and from Guangzhou immediately launched an epidemiological investigation on Friday to trace coronavirus sources and disinfect public venues Guo had visited.

Officials have urged residents to avoid infection by wearing face masks when going out, as well as paying special attention to personal hygiene and the maintenance of social distancing.