The greatest risk factor for bird flu seems to be contact with sick birds or with surfaces contaminated by their feathers, saliva or droppings. In very few instances, bird flu has been transmitted from one human to another. But unless the virus begins to spread more easily among people, infected birds present the greatest hazard.

The pattern of human transmission remains mysterious. People of all ages have contracted and died of bird flu. At this point, too few people have been infected to know all the possible risk factors for bird flu.

Jan. 26, 2013