A medical worker collects a swab sample of a resident for nucleic acid testing at a community in Yu'an District of Lu'an City, east China's Anhui Province, May 15, 2021. (Xinhua/Zhou Mu)

HEFEI/SHENYANG, May 16  -- East China's Anhui Province and northeast China's Liaoning Province have stepped up contact tracing and mass testing in efforts to contain the latest COVID-19 resurgence.

Health authorities in Anhui, where seven confirmed locally transmitted cases and seven asymptomatic carriers had been reported by Sunday noon, said all recent infections are related to an offline training session at a photo studio in Yu'an District of Lu'an City.

The cases so far are either session participants, studio employees, customers, or their close contacts, according to the provincial health commission.

Anhui on Thursday reported its first confirmed case in the recent COVID-19 resurgence, a 29-year-old female from Lu'an. As of Sunday noon, Lu'an had reported five of the seven confirmed cases in the province, while the other two emerged in the provincial capital of Hefei. All seven asymptomatic cases in Anhui were reported from Lu'an.

Gene sequencing analysis conducted by the provincial center for disease control and prevention found the coronavirus behind the cases were not the highly infectious mutant strains found in India and South Africa.

Epidemiologists are still working to determine the "patient zero," said Dong Mingpei, deputy head of the provincial health commission.

The cities of Lu'an and Hefei have both launched citywide nucleic acid tests in the wake of the new infections. As of Sunday noon, nearly 1 million people in Lu'an and about 170,000 people in Hefei tested negative for the novel coronavirus.

Experts have basically ruled out the possibility of mass infections in Anhui, Dong said.