https://www.reddit.com/r/europe/comments/fbsray/new_covid_findings_from_the_report_of_the_who/

One of the important reasons for containing the outbreak is that China is interviewing all infected people nationwide about their contact persons and then tests those. There are 1,800 teams in Wuhan to do this, each with at least 5 people. But the effort outside of Wuhan is also big. In Shenzhen, for example, the infected named 2,842 contact persons, all of whom were found, testing is now completed for 2,240, and 2.8% of those had contracted the virus. In Sichuan province, 25,493 contact persons were named, 25,347 (99%) were found, 23,178 have already been examined and 0.9% of them were infected. In the province of Guangdong, 9,939 contacts were named, all found, 7,765 are already examined and 4.8% of them were infected. That means: If you have direct personal contact with an infected person, the probability of infection is between 1% and 5%.
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"Much of the global community is not yet ready, in mindset and materially, to implement the measures that have been employed to contain COVID-19 in China. These are the only measures that are currently proven to interrupt or minimize transmission chains in humans. Fundamental to these measures is extremely proactive surveillance to immediately detect cases, very rapid diagnosis and immediate case isolation, rigorous tracking and quarantine of close contacts, and an exceptionally high degree of population understanding and acceptance of these measures."
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China can now produce 1.6 million test kits for the novel coronavirus per week. The test delivers a result on the same day. Across the country, anyone who goes to the doctor with a fever is screened for the virus: In Guangdong province, far from Wuhan, 320,000 people have been tested, and 0.14% of those were positive for the virus.