A community staff member checks a resident's body temperature at the entrance of a community in Xicheng district in Beijing, capital of China, June 17, 2020. (ZHANG YUWEI / XINHUA)

BEIJING - Beijing has imposed travel restrictions and expanded nucleic acid testing to contain the spread of the COVID-19 epidemic, local officials said on Thursday, as China's capital reported 21 newly confirmed COVID-19 cases on Wednesday.

Security inspection stations have been set up on the city's highway toll booths, giving departure permission only to those travelers with a negative nucleic acid test report, according to Pan Xuhong, deputy director of Beijing Municipal Public Security Bureau.

Confirmed cases and suspected cases, along with their close contacts and those infected with no symptoms, will not be allowed to buy airline or train tickets, he said at a news conference on Thursday morning.

Strengthening the management of risky groups by banning them from leaving the city doesn't mean there's a lockdown, said Pan Xuhong, deputy director of Beijing Municipal Public Security Bureau

At the conference, another official from the city's leading group for epidemic prevention and control also revealed that strict control methods have been implemented.

Three groups of people are not allowed to leave Beijing. First are confirmed cases, suspected cases and their close contacts, asymptomatic patients and people with fever. The second group comprises of people who have visited the Xinfadi wholesale food market in southern Beijing – where most new cases were traced back to – or had close contact with market workers since May 30. The third group are residents living in areas designated as medium- and high-risk areas.

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Apart from a 14-day medical observation, close contacts in Beijing are required to take two nucleic acid tests for the coronavirus, said Zhang Ge, deputy director of the group's branch team responsible for the work in the city's residential areas.

Moreover, all hotels in the city will no longer accept guests who have traveled to high- or medium-risk regions outside Beijing within the past 14 days. For travelers from Wuhan, Hubei province, a negative nucleic acid test report will be required.

All public entertainment places in Beijing's residential areas have been closed, according to Zhang.

In the city's high-risk areas, all public places, including schools, office buildings, hotels and restaurants, have also been shuttered, Zhang said.

"It is a crucial period for prevention and control work in Beijing. We don't encourage any unnecessary travel from Beijing to other places. If in need, travelers should carry a nucleic acid test report with a negative result," Zhang said.

Pan said that strengthening the management of risky groups by banning them from leaving the city doesn't mean there's a lockdown.

Pan also said that passengers who have bought air and train tickets to and from Beijing before Wednesday can apply for postponement and refund free of charge, and security checkpoints would be installed at highways to check the health status of people departing the city.

Meanwhile, Chinese scientists have successfully isolated the coronavirus strain that caused the latest COVID-19 outbreak in Beijing, a significant progress that will greatly aid the epidemic control and prevention.

The strain was isolated on Monday from samples collected from the respiratory tracts of infected cases at the Xinfadi market, the Chinese Center for Disease Control and Prevention said on Thursday.

Earlier Thursday, the municipal health commission said Beijing reported 21 newly confirmed COVID-19 cases transmitted locally and three new asymptomatic cases on Wednesday, the municipal health commission.

As of Wednesday, Beijing had reported 158 local cases since the first case in the latest outbreak, which is linked with Xinfadi, was reported on June 11.

'No proof' that COVID-19 can spread through food

There is no evidence that COVID-19 can spread through food products, including seafood, the National Health Commission said on Thursday.

The recent cluster of infections tied to the Xinfadi wholesale market has raised concerns about the safety of consuming seafood products and vegetables traced to the venue.

The National Health Commission said asymptomatic cases who are released from medical observations are no longer able to transmit the virus

In an article published on its official WeChat account, the commission said research shows that the novel coronavirus mainly transmits though respiratory droplets and close contact. Aerosol transmission — droplets carrying the virus that mix with the air and are inhaled — is possible if one is exposed to a highly concentrated mixture in an enclosed area for an extended period.

"Other transmission routes are yet to be confirmed," it said.

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The commission suggested using separate chopping boards for raw ingredients and cooked foods, avoid eating sashimi and salad, and peel fruits before eating. It said that steaming kitchen utensils for 15 minutes can work to thoroughly disinfect them.

People are encouraged to heat packaged cook foods before eating, and refrain from storing large bulks of vegetables during summer.

Meanwhile, the commission said asymptomatic cases who are released from medical observations are no longer able to transmit the virus.

The commission said people who have recently traveled to high-risk areas are suggested to voluntarily take tests.

Mainland reports 28 new cases

A total of 28 new cases were reported on the Chinese mainland Wednesday, of which 24 were local cases and four were imported, the National Health Commission said in its daily report earlier Thursday.

Besides the 21 local cases reported in Beijing, two others were in Hebei province and one in the Tianjin municipality, the commission said.

Two out of the four imported cases were reported in Shanghai, and one each in Shaanxi and Gansu, respectively, the commission said.

A total of 28 new cases were reported on the mainland Wednesday, of which 24 were local cases and four were imported, the National Health Commission said

No deaths related to the disease were reported while three new suspected cases were reported in Beijing, according to the commission.  

Fifteen patients were discharged from hospitals after recovery Wednesday, the commission said. There were 265 patients still being treated, including nine in severe condition.

As of Wednesday, a total of 83,293 confirmed cases had been reported on the mainland, of which 4,634 had died and 78,394 had recovered.

A total of 1,860 imported cases had been reported on the mainland by Wednesday, among which 1,769 had recovered while 91 remained hospitalized. No deaths had been reported from the imported cases. 

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The commission said there were seven suspected cases by Wednesday.

According to the commission, 5,220 close contacts were still under medical observation after 153 people were released from medical observation Wednesday.

Also on Wednesday, eight new asymptomatic cases, including two imported from overseas, were reported on the mainland. No asymptomatic case was re-categorized as a confirmed case. Three asymptomatic cases were released from medical observation.

The commission said 111 asymptomatic cases, including 63 from overseas, were still under medical observation.

By Wednesday, 1,120 confirmed cases, including four deaths, had been reported in the Hong Kong Special Administrative Region (SAR), 45 confirmed cases in the Macao SAR, and 445 in Taiwan, including seven deaths.

A total of 1,071 patients in the Hong Kong SAR, 45 in the Macao SAR, and 434 in Taiwan had been discharged from hospitals after recovery.