Fever is diagnosed by measuring body temperature using a thermometer. Normal body temperature can vary, but it is generally around 98.6°F (37°C). A fever is usually considered to be a temperature of 100.4°F (38°C) or higher. Thermometers can be used orally, rectally, axillary (underarm), or tympanically (ear) to measure temperature. In an epidemiological context, tracking fever in populations can help identify and control outbreaks.
