text:  And Jennifer Nuzzo, an epidemiologist at Brown University, says it's really not surprising that some of them were infected. It's gambling with people's lives. We're fortunate that these workers didn't get severely ill. But from everything we know about this virus, we have every reason to worry that someone could become severely ill. And Michelle, that's because bird flu can be quite lethal, although so far it has only led to mild illness in the handful of cases documented in the U.S. since April.