A medical worker in protective suit collects a swab sample from a boy for COVID-19 nucleic acid testing in the subdistrict of Baihedong in Liwan District of Guangzhou, south China's Guangdong Province, June 12, 2021.(Photo: Xinhua)

Dongguan, South China's Guangdong Province, is conducting a round of citywide nucleic acid testing for its residents on Monday after it reported one new COVID-19 infection on Sunday.

According to Dongguan's health authority, the citywide testing will not include Changan, Humen, Dalingshan and Mayong towns, which started large-scale testing on Saturday and Sunday. People entering the city also are required to take the test.

The new case confirmed on Sunday is a student surnamed Jia, 19, who lives in campus in Mayong and is the close contact of another COVID-19 patient surnamed Li, who was confirmed on Friday. The city now has two confirmed local cases as Guangdong Province races to stifle mutated virus strains from overseas.

Meanwhile, Mayong town has been sealed off.

To date, 86 people in Dongguan have been confirmed to have been in close contact with the confirmed cases, and they have been placed under medical watch.

Dongguan's health authority said on Sunday afternoon that the source of the first confirmed case in Dongguan has been identified.

The sequencing results showed that Li's positive samples are the Delta variant and Li is a local case associated with an imported patient.

Although the genome sequence for Li and that of the Guangzhou epidemic were both Delta strains, it was significantly different from that of the Guangzhou epidemic, suggesting that they were from different virus sources, a local health official said on Sunday.

Haikou, South China's Hainan Province, said on Monday that the Baoyuan Huayuan residential community in Xiuying district was put under closed management on Sunday evening after a resident there tested positive for COVID-19 on Sunday evening.

The case had flown to Dongguan via Guangdong's Shenzhen Bao'an International Airport on June 3 and returned to Haikou via the same airport on June 6.

The patient was isolated for medical observation and treatment on Monday morning and later tested negative.

The patient will be tested again in 24 hours and the result will be released then.

Other residents in the Baoyuan Huayuan community are requested to take tests and stay at home for medical observation for one day. 

Shenzhen Bao'an International Airport discovered a confirmed case on Friday, a 21-year-old waitress at the airport surnamed Zhu. Genome sequencing shows the virus she is carrying has the same origins as the three imported cases on international flight CA868 and a June 14 case, all of which were of the Delta variant, a COVID strain first detected in India.