Almost 60 per cent of people who contracted Covid-19 in the city of Wuhan, China, were asymptomatic or had symptoms so mild they were not reported to authorities, according to a study.

A group of researchers led by Chinese doctors reviewed about 26,000 laboratory-confirmed cases recorded in the city, where the coronavirus was first identified, between December and February.

They used lab tests, instead of Chinese government data, because authorities in the country did not count some cases where patients did not show symptoms.

The study, which was run by doctors from Tongji Medical College in Wuhan, Fudan University in Shanghai and Harvard University in Massachusetts, referred to asymptomatic and very mild cases as “unascertained”.

“Here, unascertained cases included asymptomatic cases and those with mild symptoms who could recover without seeking medical care and thus were not reported to authorities,” the researchers said.

“We found that at least 59 per cent of infected cases were unascertained in Wuhan, potentially including asymptomatic and mild-symptomatic cases,” they added.

The paper, which has not yet been peer reviewed, was published on the medRxiv preprint platform earlier this month.

It came as concerns have been raised about how China has recorded asymptomatic cases during its coronavirus outbreak.

Chinese government data has shown the number of people with Covid-19 who had delayed or no symptoms could have been as high as one-third of those who tested positive for the disease, according to the South China Morning Post.

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The Wuhan researchers have estimated there were more than 26,000 unascertained cases in the city by 18 February, when China was reporting about 72,000 cases on its mainland.

However, the study said the total number of infections could have been much higher than that figure, based on their models.

“We predicted the cumulative number of ascertained cases [in Wuhan] to be 26,252 by February 18, close to the actual reported number of 25,961, while the estimated cumulative number of total cases was 125,959,” the study said.