What was the differential diagnosis of patient zero from the movie Contagion?

In the movie Contagion, patient zero, Beth Emhoff, presents with flu-like symptoms after returning from a trip to Hong Kong. The differential diagnosis includes viral infections like influenza and other respiratory viruses, as well as bacterial infections such as pneumonia or meningitis. Additionally, the possibility of an exotic zoonotic disease, given her recent travel, is considered. Ultimately, the rapid progression of her symptoms leads to the identification of a novel virus.