Fever is a rise in body temperature in response to infection, injury, or inflammation (see Biology of Infectious Disease: Fever).
Body temperatures vary, and temperature elevations up to 100.3° F (about 38° C) can be normal in healthy children. Therefore, minor temperature elevations that do not distress a child do not require medical attention. Temperatures of 100.4° F (about 38° C) and higher are considered abnormal and usually deserve attention, particularly in infants younger than 3 months.
Causes and Symptoms
Fever is usually the result of common infections, such as colds and gastroenteritis. These infections are usually viral and resolve without treatment. Less commonly, fever develops because of infection in the ear, lung, bladder, or kidney. These are usually bacterial infections that require antibiotics. Rarely, fever in infants is the only sign of a bloodstream infection (occult bacteremia—see Bacterial Infections in Infants and Children: Occult Bacteremia), which can lead to meningitis and overwhelming infection (sepsis), two life-threatening conditions. Children with these kinds of infection usually appear ill. Many conditions besides infection cause fever in children, but all are rare. Unlike fevers that occur with common infections, these fevers persist for more than a few days.
Fevers can occur after routine vaccinations and are not a reason to avoid recommended vaccines. Giving the infant acetaminophen or ibuprofen at the time of vaccination and afterward minimizes the risk of getting a fever or lowers the fever itself.
Infants with fever are usually irritable and may not sleep or feed well. Older children lose their interest in play, although sometimes children with high fevers appear surprisingly well. The irritability and disinterest that fever usually causes worsen the higher the fever gets. Occasionally, a rapidly rising fever can cause seizures (febrile seizures), and quite rarely, a fever gets so high that children become lethargic and unresponsive.
Diagnosis and Treatment
Detecting fever is not a challenge, but determining its cause can be. If the fever is low grade (100.3° F [about 38° C] or below) and of short duration, no testing or treatment may be needed. In other cases, knowledge of the child's symptoms and a thorough examination help doctors find the cause. In general, any infant with a temperature of 100.4° F (about 38° C) or higher should be seen by a doctor, as should older children with higher or recurring fevers or complaints of pain.
In infants younger than 2 months of age who have a fever, doctors may order blood and urine tests and perform a spinal tap (lumbar puncture—see Symptoms and Diagnosis of Brain, Spinal Cord, and Nerve Disorders: Tests for Brain, Spinal Cord, and Nerve Disorders) to look for occult bacteremia, urinary tract infection, and meningitis. The reason for these tests is that in infants, the source of fever is difficult to determine. They are also at risk of serious infection compared with older children because of their immature immune system. Doctors may also order an x-ray if the infant's breathing is abnormal. For infants older than 2 months of age, testing may not be needed, but many doctors order blood and urine tests and perform a spinal tap if the source of the fever is not obvious and the child appears ill. For children 3 months of age and older, doctors rely more on the child's behavior and physical examination to determine which tests to order. Doctors may order blood and urine tests for children younger than 3 years old with high fevers if they cannot determine the source of fever after examining the child.
Most fevers do not require treatment except to make the child feel better and thus more willing to drink, avoiding dehydration. Acetaminophen and ibuprofen are used. Aspirin is not safe for lowering fever because it can interact with certain viral infections and cause a serious condition called Reye's syndrome (see What Is Reye's Syndrome?). A warm (not cold) bath can sometimes make an older child feel better by reducing the fever. Rubbing the child down with alcohol or witch hazel is not recommended. Alcohol or witch hazel may have harmful fumes, come into contact with the eyes, or be accidentally ingested.
Additional treatment depends on the child's age and cause of the fever. Rarely, fevers persist and doctors are unable to determine the source even after extensive testing. This type of fever is called fever of unknown origin (see Biology of Infectious Disease: Testing).
Last full review/revision February 2009 by Elizabeth J. Palumbo, MD