https://www.cdc.gov/flu/pandemic-res...-pandemic.html
The 2009 Swine Flu was first detected in the US, although yes there is speculation that it may have originated across the border. It may just be that the US had the technical capacity and epidemiological nous to detect it first.
Anyway Mexico/US/China/Saudi or Africa, it doesn’t really matter: finger-pointing is not constructive unless you’re a politician trying to defend your job (after spectacularly dropping the ball). Learning from previous crises to avoid or contain the next is key, like HKG did by learning after SARS.