A few weeks ago they had only a handful of cases
This isn't true. Covid19 started in December in China and as they denied it and pretended it wasn't happening for a while, the number of cases were completely unchecked.
On 30 December he sent a message to fellow doctors in a chat group warning them to wear protective clothing to avoid infection.
Four days later he was summoned to the Public Security Bureau where he was told to sign a letter. In the letter he was accused of "making false comments" that had "severely disturbed the social order".
He was one of eight people who police said were being investigated for "spreading rumours" Local authorities later apologised to Dr Li.
In his Weibo post he describes how on 10 January he started coughing, the next day he had a fever and two days later he was in hospital. He was diagnosed with the coronavirus on 30 January.
It took 10 days for the whistleblower to catch it, a few days to be hospitalised and another 2 weeks for him to be diagnosed. And there would have been a lot of cases in the 10 days before he caught it while they were denying it. China didn't control the outbreak, they are controlling the result of it. Thankfully, the rest of the world have been able to control it from outset so it shouldn't reach the levels seen in China. But who knows?
This is why quarantine is important