MODEL RELEASED. Doctor visits unwell child. A general practice doctor on a home visit examines a child who is sick in bed with fever. The doctor is touching the child's forehead with her hands to check body temperature. 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.