VOI - Voice of Indonesia | RRI - Radio Republik Indonesia

Security guards and medical workers in protective suits walk at a street that has been sealed off, following the coronavirus disease (COVID-19) outbreak, in Beijing, China, Apr 7, 2022. (Reuters/Tingshu Wang) - 

Shanghai's unusually high proportion of asymptomatic cases among its reported COVID-19 infections compared with the rest of China, could be partly explained by blurred lines between "mildly symptomatic" and asymptomatic cases.

Shanghai's unusually high share of asymptomatic COVID-19 infections has raised suspicions that the city is classifying mildly symptomatic cases, a different counting method compared to the rest of the country, with comments from a local health adviser adding to the doubts.

Authorities in China's financial centre ordered a lockdown in response to the worst outbreak in the country since the virus first emerged in Wuhan in late 2019.

Shanghai counted more than 20,000 new cases on Apr 7, but the asymptomatic rate has stood at around 97 per cent, far higher than anywhere else in the world, where it has been closer to 50 per cent.

Fu Chen, head of the municipal Center for Disease Control and Prevention, said in a written reply to Reuters' questions that Shanghai's rapid surveillance testing was contributing to the big asymptomatic numbers by catching infections earlier.

He also said high vaccination rates were also having an impact, as vaccinated people are less likely to show symptoms.

Fu did not say directly that Shanghai was using less strict diagnostic criteria, but he did suggest the numbers in the rest of China would be comparable if "mildly symptomatic" cases were included in the asymptomatic tally.

"Recently, a press conference of the State Council's joint prevention and control mechanism also said that the proportion of mildly symptomatic and asymptomatic infections in hospitals across the country exceeds 95 per cent," Fu noted.

The city government did not immediately respond to a request for comment on whether Shanghai uses different diagnostic standards compared to elsewhere.

Asymptomatic cases in China are defined as those that test positive for coronavirus but have no "relevant" clinical manifestations, Fu said.

The national guidelines define asymptomatic cases as those testing positive but showing no clinical symptoms like fever, and no signs of COVID-19 in their lungs, as determined by a CT scan.

Asymptomatic cases are reclassified if symptoms appear later.

"Mildly symptomatic" cases are those that show light symptoms but no signs of pneumonia after a chest scan.

The national standards say that determining an asymptomatic case requires a chest scan, which would put Shanghai's medical system under immense pressure given the scale of the current outbreak. It is unclear how many asymptomatic cases in Shanghai or elsewhere underwent lung CT scans.

Paul Hunter, a professor of medicine at the University of East Anglia, told Reuters it would be "absolutely crazy" for anywhere to scan everybody who tested positive.

In Jilin province in China's northeast, site of another major outbreak, asymptomatic cases have accounted for less than half of reported infections, though the figure has been increasing steadily to around 60 per cent in recent days.

But according to Reuters calculations, if Jilin's mildly symptomatic cases are added to the asymptomatic tally, the share would rise to more than 96 per cent - similar to Shanghai's asymptomatic numbers//CNA