The primary causes of persistently high mortality are infectious diseases. Particularly important are diseases for which effective immunization is not widely available, such as diarrhea or acute respiratory infections. Diarrheal and acute respiratory infection are common childhood diseases throughout the world. Acute respiratory infection is an infection that may interfere with normal breathing. It usually begins as a viral infection in the nose, trachea or lungs. If the infection isn't treated, it can spread to the entire respiratory system.