Response or nonresponse to medications does not predict whether or not a child has a serious illness.With respect to the effect of antipyretics on the risk of death in those with infection, studies have found mixed results as of 2019. Animal models have found worsened outcomes with the use of antipyretics in influenza as of 2010 but they have not been studied for this use in humans. Epidemiology
Fever is one of the most common medical signs. It is part of about 30% of healthcare visits by children, and occurs in up to 75% of adults who are seriously sick. About 5% of people who go to an emergency room have a fever. History
A number of types of fever were known as early as 460 BC to 370 BC when Hippocrates was practicing medicine including that due to malaria (tertian or every 2 days and quartan or every 3 days). It also became clear around this time that fever was a symptom of disease rather than a disease in and of itself.Infections presenting with fever were a major source of mortality in humans for about 200,000 years. Until the late nineteenth century, approximately half of all humans died from infections before the age of fifteen.An older term, febricula (a diminutive form of the Latin word for fever), was once used to refer to a low-grade fever lasting only a few days.
Norepinephrine increases thermogenesis in brown adipose tissue, and muscle contraction through shivering raises the metabolic rate.If these measures are insufficient to make the blood temperature in the brain match the new set point in the hypothalamus, the brain orchestrates heat effector mechanisms via the autonomic nervous system or primary motor center for shivering. These may be:
Increased heat production by increased muscle tone, shivering (muscle movements to produce heat) and release of hormones like epinephrine; and
Prevention of heat loss, e.g., through vasoconstriction.When the hypothalamic set point moves back to baseline—either spontaneously or via medication—normal functions such as sweating, and the reverse of the foregoing processes (e.g., vasodilation, end of shivering, and nonshivering heat production) are used to cool the body to the new, lower setting.This contrasts with hyperthermia, in which the normal setting remains, and the body overheats through undesirable retention of excess heat or over-production of heat. Hyperthermia is usually the result of an excessively hot environment (heat stroke) or an adverse reaction to drugs. Fever can be differentiated from hyperthermia by the circumstances surrounding it and its response to anti-pyretic medications.In infants, the autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis).Increased heart rate and vasoconstriction contribute to increased blood pressure in fever. Pyrogens
A pyrogen is a substance that induces fever. In the presence of an infectious agent, such as bacteria, viruses, viroids, etc., the immune response of the body is to inhibit their growth and eliminate them.