Well they did not send infected ppl from Wuhan to Bejing or any other part of China, just to the rest of the world.
Italy was easy because there are thousands of Chinese ppl working there.
Always going back and forth.
Note: China bought many companies in Italy, and left them there so products could still say Made in Italy.
What you're suggesting is an actual quarantine of Wuhan a city larger the New york city actually worked.
That reminds me of Get Smart "would you believe quarantine of an apartment building all breathing the same air?"
No? "how about a quarantine of Chen Qiushi?" (head rolls back and fourth.. as saying, "what would you believe?")