There's also some data coming out of Wuhan around antibody testing. The methodology is not as well formed as the study in the OP but there is still value in the data.

> Wuhan’s Zhongnan Hospital found that 2.4% of its employees and 2% to 3% of recent patients and other visitors, including people tested before returning to work, had developed antibodies, according to senior doctors there.

Additional antibody testing is also underway in Wuhan.

Source: https://www.wsj.com/articles/wuhan-starts-testing-to-determi...