Asymptomatic people may be infecting others despite officials saying risk of this is low

Two weekends ago, Wang, a 59-year old cleaner who works at a library in Henan province, accompanied her former classmate Zhang home for China’s tomb-sweeping holiday, when families tend to the graves of their ancestors. She met Zhang, a local doctor, at a bus stop and the two drove out to the countryside. They shared three meals together.

On Tuesday last week, Wang developed a cough and two days later, a fever. Her son took her to hospital where she was tested for Covid-19. On Saturday, she became not only the first person in her province in 30 days to catch coronavirus via local transmission, but one of the country’s few new infections.

Wang’s case, detailed by Henan’s health commission, has raised alarm because of the possibility she contracted the virus from Zhang, an asymptomatic or “silent” carrier. These are people who officials have repeatedly said pose a low risk of contagion and who are not reflected in the government’s published tally of confirmed cases.

On Wednesday, Zhang and two other doctors in Jia county in Pingdeshan tested positive for the virus but had no symptoms. All three had shared a meal together on 13 March after one of the group had been quarantined for 14 days as a precautionary measure after returning from Wuhan, the centre of the outbreak.

As China relaxes lockdown measures and people return to work, they are concerned about the possibility that asymptomatic carriers will continue spreading the virus. For the last two weeks, health authorities have reported an almost zero rate of local transmission of the virus, with almost all new cases coming in from outside the country. But critics say officials are downplaying the outbreak by not including asymptomatic cases.

China has not released data for the number of asymptomatic cases, but Chinese researchers estimated that 59% of those who contracted the virus had mild or no symptoms. Documents seen by the South China Morning Post reportedly showed more than 40,000 asymptomatic patients that would not have been included in China’s total number of infections of more than 80,000.

Such patients, usually found by tracing the contacts of confirmed cases, are quarantined for 14 days and released if they do not show any symptoms. But the number of reports of new cases has started to worry the public, as well as authorities who pledged on Monday to step up prevention and control of such infections.

“This case is not the only one. Everyone thinks there is no hidden danger and that the only risk is the imported infections from abroad,” wrote one commentator online, in response to the new infection in Henan. “So-called low-risk areas are not to be believed. Bureaucrats everywhere have already begun covering up,” another said.

In an editorial on Sunday, the financial news magazine Caixin called on the government to publish data on asymptomatic carriers. “Within China, transmission caused by asymptomatic infections has occurred many times. The number needs to be made public as soon as possible. Investigation and and research is needed to raise the public’s alertness,” it said.

Since 18 March there have been five confirmed cases of asymptomatic infection in Dongguan in Guangdong province, a major manufacturing hub. Last week, authorities formally arrested a man in Beijing who was diagnosed as an asymptomatic carrier in mid-February. He repeatedly visited grocery stores, pharmacies and other public places against regulations. His mother has been infected and 20 other close contacts have now been quarantined.

Two recently confirmed patients, one in Gansu province and one in Guangdong province, had both previously been in Xianning county in Hubei where no locally transmitted cases have been reported since late February. This has led to conjecture that they contracted the virus from asymptomatic carriers in the area.

Authorities have now tracked down 15 people in close contact with Wang in Henan, and 53 people who could have been infected by the three doctors have now been quarantined.

The government has tried to assure the public. China’s top respiratory disease expert Zhong Nanshan told the state broadcaster CGTN that while asymptomatic patients who have been in close contact with confirmed patients can be “very infective”, he did not believe they posed a “big problem” in China.

“I suppose we don’t have too many asymptomatic patients. If we did, they would be transmitting to other people and pushing the number higher,” he said.

Chinese premier Li Keqiang chaired a meeting where he said the government would step up prevention and control of asymptomatic infections, through screening, quarantines and tracking contacts of confirmed cases, according to state media on Monday. Last week, he called on health officials to investigate whether asymptomatic people were contagious, in order to help the country’s ongoing prevention plans, and ordered officials “not to cover up” cases.

But the infectious disease expert Zhang Wenhong, said at a symposium on Friday that asymptomatic carriers would continue to pose a major risk, even as China took measures, such as temporarily banning foreigners from entering the country.

“Now, we only allow Chinese people to come back. But when our country’s doors open again, there will be large numbers coming in. When they are asymptomatic, the risk is great.”

Additional reporting by Wu Pei Lin