For most people, influenza virus infection is just a nasty experience, but in some instances it can lead to illnesses that are more serious. The most common complications of influenza are bronchitis and secondary bacterial pneumonia. These illnesses may require treatment in a hospital and can be life-threatening especially in "high-risk" people e.g. the elderly and people suffering from chronic heart disease. During the 1918 pandemic (see below), though, influenza also caused serious illness in young healthy individuals.