. Feverish child. A young boy suffering fever lies in bed with his teddy bear. The child's rosy cheeks are an indication of fever. Fever, also known as pyrexia, is defined as a body temperature above 37 Celsius (98.6 Fahrenheit) if measured in the mouth. Most fevers are caused by bacterial or viral infections and may be accompanied by other symptoms such as shivering, sweating, thirst and hot skin. MODEL RELEASED