A staff checks the nucleic acid test kit at the plant of Luoyang Ascend Biotechnology Co., Ltd in Luoyang, central China's Henan Province, March 4, 2020. Photo: Xinhua

The discovery of asymptomatic patients has prompted a county in Central China's Henan Province to go back to "wartime status" by locking down all villages and communities, raising questions over whether cities where there are silent virus carriers should impose lockdowns again. 

The county is the first known region to restore lockdown due to the discovery of asymptomatic patients. 

On March 29, a confirmed case reported by the Henan Provincial Health Commission ended the 30-day run of no new local confirmed cases in the province, and also led to the discovery of three asymptomatic infections, who are doctors in the local people's hospital in Jiaxian, a county under the jurisdiction of Pingdingshan city.

The three virus carriers showed no symptoms but tested positive for novel coronavirus in a physical checkup of frontline medical workers.

Immediately following the report of the three silent virus carriers on March 29, the Jiaxian county government brought back a series of measures to deal with the virus spread, including suspension of bus and taxi services and strict imposition of anti-epidemic measures at business venues. 

The county's anti-epidemic leading group said the county will go back to "wartime status." 

In a statement, the group said all villages and communities must be accessed through only one entrance, and people are only allowed to go out with a permit, must wear masks and have their body temperatures taken. Those who need to go out for work must get a certificate from their employers. 

The local government did not say when the county will return to normal status.

A working group led by local police will locate every person who has had close contacts with the asymptomatic patients, Zhou Bin, the Party chief of Pingdingshan city, said on Tuesday in a meeting with medical experts. 

Provinces and autonomous regions including Northeast China's Liaoning and Northwest China's Inner Mongolia have reported asymptomatic virus carriers but have yet to announce city lockdowns. 

Restoring a citywide lockdown is a very cautious and necessary measure to prevent the spread of the virus caused by asymptomatic patients, said Zhou Zijun, a professor at the Peking University School of Public Health. 

He called on other places where asymptomatic patients have been found to impose lockdowns following the measures taken by Jiaxian county.

The cost of asymptomatic virus carriers spreading the disease is huge. People around asymptomatic virus carriers have no immunity, so if an individual is found to be infected, that person will infect other people quickly. 

The situation in the US testifies the capability of asymptomatic virus carriers in spreading the disease, Zhou said.

Asymptomatic patients are mainly discovered through four channels: medical observation of people who have come into close contacts with COVID-19 patients, investigation of cluster epidemics, tracking of infection sources, and tests on people who have had a travel history or residence history in epidemic areas at home or abroad.