Most human cases of bird flu in North America have been mild, a fact that’s underscored by a new study of the first 46 confirmed human H5N1 infections in the United States this year. But the case of an ill Canadian teen stands out because of its severity and because the source of exposure remains a mystery.

A sharp increase in norovirus cases is sweeping the United States, according to the latest data from the Centers for Disease Control and Prevention (CDC). Often called the "stomach flu," norovirus is a leading cause of gastroenteritis,

The latest government data shows that cases of a fast-spreading stomach bug are surging in parts of the United States. The most recent numbers from the U.S.

In December alone, the CDC reported five separate outbreaks on four different ships -- sickening more than 800 people. All of the outbreaks were caused by the highly contagious norovirus.

Hundreds of people on cruise ships have been sickened in five separate outbreaks of gastrointestinal illness this month, according to the U.S. Centers for Disease Control and Prevention. In all cases combined,