Rob Stein:

The U.S. government yesterday dispatched experts to help investigate outbreaks of a mysterious pneumonia-like illness in Hong Kong and Hanoi that have killed an American businessman and sickened dozens of hospital workers....

Stephen Morse, an infectious-disease expert at Columbia University, said that the biggest concern is that the outbreaks are the beginning of a global flu epidemic.

"In the back of everyone's mind, of course, is the 1918-1919 Spanish flu. That's the fear," said Morse, referring to the most deadly global flu pandemic in history. Flu viruses historically have originated in Asia and spread, he said.

I keep forgetting why flu viruses originate in Asia; most researchers believe that teeming, tropical southern China, where man and domestic animals, particularly pigs and poultry, live in close contact, is a primary source of new influenza strains.