WUHAN, April 14 (Xinhua) -- To learn the occurrence of asymptomatic cases, Wuhan, the hardest-hit city in the coronavirus outbreak in China, launched an epidemiological sampling survey on local residents Tuesday.

The survey started in Jiangxia District on Tuesday morning. A total of 880 residents from eight sub-districts received nucleic acid and antibody tests for free.

The survey will cover a total of 11,000 residents from 13 administrative districts in Wuhan. To ensure the authenticity and accuracy of the data, the sampling survey adopts the principle of random sampling at fixed points. One hundred residential communities will be selected as the survey points.

Experts still need to further understand the transmission characteristics, epidemiological characteristics and pathogenic path of the novel coronavirus, explore its epidemic regularity, and perfect the prevention measures, said Ding Gangqiang, leader of the epidemiological sampling survey team sent by the Chinese Center for Disease Control and Prevention to Wuhan.

"We have launched such sampling surveys in Wuhan and nine municipalities and provinces including Beijing, Liaoning, Shanghai, Jiangsu, Zhejiang, Hubei, Guangdong, Sichuan and Chongqing to learn people's COVID-19 antibody level and provide scientific basis for the adjustment of the prevention and control strategy," Ding said.

Zhu Huaqiao, director of the health bureau of Jiangxia District, said the epidemiological sampling survey can help reveal the infectiousness and dynamic changes of the novel coronavirus.

To ensure the representativeness, authenticity and accuracy of the sampling, it is required that the sampled objects must all be eligible family members who have lived in the communities for no less than 14 days from January to March. Grassroots epidemic prevention personnel, security guards, police, cadres, taxi drivers, other volunteers and related staff at the front line of epidemic prevention and control are also included in the sampling range.