"We just don't know why there haven't been cases," said Jennifer Nuzzo, director of the Pandemic Center at Brown University. "I think we should assume there are infections that are occurring in farmworkers that just aren't being detected."
The H5N1 bird flu has been spreading widely among wild birds, poultry and other animals around the world for several years, and starting early last year became a problem in people and cows in the U.S.
In the last 14 months, infections have been reported in 70 people in the U.S.—most of them workers on dairy and poultry farms. One person died, but most of the infected people had mild illnesses.
The most recent infections confirmed by the Centers for Disease Control and Prevention were in early February in Nevada, Ohio and Wyoming.
