Contagion: How contagious is the new "mystery bug" from Southeast Asia? Very:

Seven people who came down with a mysterious form of pneumonia, including two who have died, spent time on the same floor of a Hong Kong hotel before the outbreak prompted a global alert, officials said Wednesday.

One was a 64-year-old medical professor from Guangzhou, China, who died in Hong Kong on March 4, and one was a 78-year-old woman from Toronto, who died after returning to Canada, according to a Hong Kong government spokeswoman.

The other visitors of the Metropole Hotel who became sick were three Singaporean women, two of them age 23 and one 33; a 72-year-old Canadian man; and a 26-year-old Hong Kong man who had gone to the hotel to see a friend, said Dr. Margaret Chan, director of the Hong Kong Health Department.