-- Xi'an, capital of northwest China's Shaanxi province, launched a new round of citywide nucleic acid testing Monday and strengthened its anti-epidemic measures to curb the spread of the latest COVID-19 resurgence.

-- The viral genome sequencing of 137 locally transmitted COVID-19 cases in the outbreak identified the strains as the highly infectious Delta variants, which are highly homologous with imported cases of an inbound flight on Dec 4.

-- The megacity, with a population of 13 million, imposed closed-off management for communities and villages last Thursday.

-- The city has now set up more than 5,000 sample collecting venues, with more than 31,000 sample collectors.

-- Under the intensified anti-epidemic efforts, 135,000 sat the exam in Xi'an.

XI'AN -- Xi'an, capital of northwest China's Shaanxi province, launched a new round of citywide nucleic acid testing Monday and strengthened its anti-epidemic measures to curb the spread of the latest COVID-19 resurgence.

The city reported 150 new locally transmitted COVID-19 cases on Sunday, bringing the total number of locally transmitted confirmed COVID-19 cases to 635 in the latest rebound since Dec 9, said the provincial health commission.

EFFICIENT EPIDEMIOLOGICAL SURVEY

On Dec 9, the city reported a locally transmitted COVID-19 case, a staffer engaged in disinfection at a quarantined hotel for inbound flights. Many locally transmitted COVID-19 cases have emerged since then.

The viral genome sequencing of 137 locally transmitted COVID-19 cases in the outbreak identified the strains as the highly infectious Delta variants, which are highly homologous with imported cases of an inbound flight on Dec 4, said Liu Feng, director of the provincial center for disease control and prevention.

"Many positive cases didn't show obvious symptoms in the initial stage. Therefore, they tended to ignore their physical condition, which led to the rapid spread of the virus inadvertently," said Wei Xiaoli, deputy director of the city's disease control and prevention center.

Epidemiological investigation found that the trajectories of the positive cases are complex and involve a wider area, Wei said.

INTENSIFIED MEASURES

The megacity, with a population of 13 million, imposed closed-off management for communities and villages last Thursday. Residents have also been asked not to leave the city unless necessary.

Long-distance passenger transport lines have been suspended, except for freight vehicles transporting epidemic prevention materials and daily necessities.

Taxis and drivers working for online ride-hailing platforms may not enter medium or high-risk areas or travel outside the city.

"For Xi'an, intensified control and screening measures are urgent to block the virus as soon as possible," said Zhang Boli, an academician of the Chinese Academy of Engineering.

"I estimate the transmission will be cut off in mid-January and the outbreak can be completely put under control in late January. It is very possible," he said in a recent media interview.

The city has conducted several rounds of citywide nucleic acid testing. "The massive tests are conducive to early detection, quarantine, and interruption of the disease, and it minimizes the possibility of transmission," said He Wenquan, a senior official with the Xi'an municipal government.

The city has now set up more than 5,000 sample collecting venues, with more than 31,000 sample collectors. More than 1,200 mobile sample collecting teams have also been dispatched to construction sites, shops, and stalls to provide more access for residents.

"All confirmed cases have been quarantined and treated in a designated hospital. National- and provincial-level experts have been invited to improve the epidemic prevention and control efforts and treatment at the hospital," said Lyu Yongpeng, deputy director of the municipal health commission. Lyu added that traditional Chinese medicine and Western medicine are adopted in the treatment, and all patients are in stable condition.

China's annual postgraduate entrance exam is scheduled from Dec 25 to 27 this year, with some 4.6 million candidates.

Under the intensified anti-epidemic efforts, 135,000 sat the exam in Xi'an. To minimize the impacts on the exam, the city government has tailored exam plans for the examinees, including those infected and close contacts.