The transmission chain and source of the virus of two recently locally transmitted confirmed COVID-19 cases in Chongqing's Jiangjin district was found to be related to a confirmed case in Macao, Chongqing health authorities said on Thursday evening.

According to epidemiological investigators, the two confirmed patients – a couple from Jiangjin – went to Emperor Qinshihuang's Mausoleum Site Museum in Xi'an, Shaanxi province, on July 23, and intersected with the person from Macao who was later confirmed as infected. That person, a woman surnamed Ou, had visited the museum at the same time.

The couple traveled around Xi'an from July 21 to 24 and then returned to Jiangjin.

There were infection risks identified on Ou's flight from Zhuhai to Xi'an on July 19. On the same aircraft, which went from Nanjing to Zhuhai, two cases of COVID-19 were reported in Guangdong province. Ou passed the virus to her parents later.

On Tuesday, Ou and her parents tested positive for the virus in Macao, local authorities said.

Gene sequencing from samples collected from patients in Jiangjin were consistent with those of the two confirmed cases in Guangdong, as well as with Ou's parents in Macao. Ou's sample is undergoing thorough gene sequencing.