Acute respiratory tract infections are the most common illnesses in all individuals, regardless of age or gender. Epidemiologic surveys and community-based studies conducted since the beginning of the 20th century have determined the rates of illness and the pathogens involved in such infections. These studies have shown that rhinoviruses cause the great majority of these respiratory illnesses, and their findings have examined the means of transmission of respiratory illness. More recently, advances in diagnostic techniques have enabled more complete identification of the viruses involved in respiratory infections, which has aided in the ability to direct specific therapeutic agents at the causative pathogens.