Over 3 per cent of people in Wuhan may have had Covid-19, possibly with no or mild symptoms, studies say

Researchers carried out antibody tests on samples from health care workers, family members and hotel staff from the outbreak epicentre in China

Separate study concludes that results of nucleic acid testing may reflect just a fraction of infections in the city

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A resident takes a nucleic acid test for Covid-19 in Wuhan. Photo: Xinhua

Published: 12:00pm, 12 Jun 2020Updated: 12:50pm, 12 Jun 2020

Two separate studies that involved antibody testing for Covid-19 suggest more than 3 per cent of people in Wuhan – a city of 11 million – may have previously had infections, possibly with no or very mild symptoms.

One team of Chinese scientists tested 17,368 people in Wuhan – where the first cases were reported in December – and other cities in China from March 9 to April 10, aiming to assess how prevalent the disease had been.

While nucleic acid tests are used to identify whether someone has contracted Covid-19 at the time they are ill, testing for antibodies – blood proteins produced by the immune system to fight the disease – is an important way to determine, later on, how many people were infected. It can also indicate whether they had asymptomatic or subclinical infections, meaning the symptoms were so mild that they did not notice them.

Tests for two types of antibodies found that 3.2 per cent to 3.8 per cent of the blood samples from Wuhan were positive, meaning they had previously been infected with Covid-19, according to the peer-reviewed study published in Nature Medicine last week.

The research was conducted by scientists from Guangzhou, Chongqing, Sichuan, Hong Kong and other Chinese cities.

Among those tested were 714 health care workers, 3.8 per cent of whom were found to have been infected with Covid-19. The proportion was the same, 3.8 per cent, for 346 staff at hotels where health care workers treating Covid-19 patients were staying. And among the 219 family members of health care workers tested, antibodies were found in 3.2 per cent.

The study found that people aged over 65 had a higher prevalence of antibodies.

But its authors noted that since the study was not based on a random sample, there could be bias and more research was needed to get a better estimate of the total number of infections in Wuhan during the outbreak.