Viral infections of the lower respiratory tract

Viral infections of the lower respiratory tract are very frequent in children, especially during the first three years of life. Most viral respiratory infections have a clear predominance of seasonal incidence, essentially being detected during the cold months of the year. In general, they are not serious conditions, since they only cause deaths in very young children with cardiac or baseline respiratory diseases. Exceptions are the new coronavirus infections initiated in China in 2002, that give rise to a serious disease ("serious acute respiratory syndrome"), although at least now, not in children, and the "bird flu" rediscovered in the winter of 2003 to 2004, presently confined to Asia, which does cause mortality in previously healthy children. The respiratory viruses give rise to two main clinical syndromes in the lower respiratory pathways: bronchiolitis and pneumonia, with existence of overlapping and mixed or intermediate pictures among them and also with involvement of the larynge and trachea. None of theses clinical pictures is associated to a single respiratory virus, although each one of them is clearly related with one or several etiological agents.