Fever (also known as pyrexia or controlled hyperthermia) is a common medical sign characterized by an elevation of temperature above the normal range of 36.5–37.5 °C (98–100 °F) due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.
Technically, any body temperature above the normal oral measurement of 98.6 F (37 C) or the normal rectal temperature of 99 F (37.2 C) is considered to be elevated. However, these are averages, and one's normal body temperature may actually be 1 F (0.6 C) or more above or below the average of 98.6 F. Body temperature can also vary up to 1 F (0.6 C) throughout the day.
Also, the body's defense mechanisms seem to work more efficiently at a higher temperature. Fever is just one part of an illness, many times no more important than the presence of other symptoms such as cough, sore throat, fatigue, joint pains or aches, chills, nausea, etc.
As a person's temperature increases, there is, in general, a feeling of cold despite an increasing body temperature. Once the new temperature is reached, there is a feeling of warmth. A fever can be caused by many different conditions ranging from benign to potentially serious. There are arguments for and against the usefulness of fever, and the issue is controversial. With the exception of very high temperatures, treatment to reduce fever is often not necessary; however, antipyretic medications can be effective at lowering the temperature, which may improve the affected person's comfort.
Fever differs from uncontrolled hyperthermia in that hyperthermia is an increase in body temperature over the body's thermoregulatory set-point, due to excessive heat production and/or insufficient thermoregulation.
The pattern of temperature changes may occasionally hint at the diagnosis:
Continuous fever: Temperature remains above normal throughout the day and does not fluctuate more than 1 °C in 24 hours, e.g. lobar pneumonia, typhoid, urinary tract infection, brucellosis, or typhus. Typhoid fever may show a specific fever pattern, with a slow stepwise increase and a high plateau. (Drops due to fever-reducing drugs are excluded.)
Intermittent fever: The temperature elevation is present only for a certain period, later cycling back to normal, e.g. malaria, kala-azar, pyaemia, or septicemia. Following are its types:
Quotidian fever, with a periodicity of 24 hours, typical of Malaria
Tertian fever (48 hour periodicity), typical of Malaria
Quartan fever (72 hour periodicity), typical of Plasmodium malariae.
Remittent fever: Temperature remains above normal throughout the day and fluctuates more than 1 °C in 24 hours, e.g., infective endocarditis.
Pel-Ebstein fever: A specific kind of fever associated with Hodgkin's lymphoma, being high for one week and low for the next week and so on. However, there is some debate as to whether this pattern truly exists.
A neutropenic fever, also called febrile neutropenia, is a fever in the absence of normal immune system function. Because of the lack of infection-fighting neutrophils, a bacterial infection can spread rapidly; this fever is, therefore, usually considered to require urgent medical attention. This kind of fever is more commonly seen in people receiving immune-suppressing chemotherapy than in apparently healthy people.
Febricula is an old term for a low-grade fever, especially if the cause is unknown, no other symptoms are present, and the patient recovers fully in less than a week.
Hyperpyrexia is a fever with an extreme elevation of body temperature greater than or equal to 41.5 °C (106.7 °F). Such a high temperature is considered a medical emergency as it may indicate a serious underlying condition or lead to significant side effects. The most common cause is an intracranial hemorrhage. Other possible causes include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm.
Infections are the most common cause of fevers, however as the temperature raises other causes become more common. Infections commonly associated with hyperpyrexia include: roseola (acute disease of infants and young children in which a high fever and skin rash occur), rubeola (measles) and enteroviral infections. Immediate aggressive cooling to less than 38.9 °C (102.0 °F) has been found to improve survival. Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's temperature regulation mechanism sets the body temperature above the normal temperature, and then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point.
Hyperthermia is an example of a high temperature that is not a fever. It occurs from a number of causes including heatstroke, neuroleptic malignant syndrome, malignant hyperthermia, stimulants such as amphetamines and cocaine, idiosyncratic drug reactions, and serotonin syndrome.
A fever is usually accompanied by sickness behavior, which consists of lethargy, depression, anorexia, sleepiness, hyperalgesia, and the inability to concentrate.
Pathophysiology
Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypothalamus, which generates a systemic response back to the rest of the body, causing heat-creating effects to match a new temperature level.
In many respects, the hypothalamus works like a thermostat. When the set point is raised, the body increases its temperature through both active generations of heat and retaining heat. Vasoconstriction both reduces heat loss through the skin and causes the person to feel cold. If these measures are insufficient to make the blood temperature in the brain match the new setting in the hypothalamus, then shivering begins in order to use muscle movements to produce more heat. When the fever stops, and the hypothalamic setting is set lower; the reverse of these processes (vasodilation, end of shivering and non-shivering heat production) and sweating 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.
A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body. The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen. Pyrogenicity can vary: In extreme examples, some bacterial pyrogens known as superantigens can cause rapid and dangerous fevers. Depyrogenation may be achieved through filtration, distillation, chromatography, or inactivation.
The brain ultimately orchestrates heat effect or mechanisms via the autonomic nervous system. These may be:
Increased heat production by increased muscle tone, shivering, and hormones like epinephrine
Prevention of heat loss, such as vasoconstriction.
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.
•In the second part of a woman's menstrual cycle, her temperature may go up by 1 degree or more.
•Physical activity, strong emotion, eating, heavy clothing, medications, high room temperature, and high humidity can all increase your body temperature.
Management:
Fever should not necessarily be treated. Most people recover without specific medical attention. Although it is unpleasant, fever rarely rises to a dangerous level even if untreated. Damage to the brain generally does not occur until temperatures reach 42 °C (107.6 °F), and it is rare for an untreated fever to exceed 105 °F (41 °C).
In general, people are advised to keep adequately hydrated, as the most significant risk of complications is dehydration. Water is generally used for this purpose. The risk of hyponatremia induced by increased fluid intake can be reduced through the use of appropriately formulated oral rehydration solutions. Other options include ice pops, juice, and other non-alcoholic drinks.
Some limited evidence supports sponging or bathing feverish children with tepid water. The use of a fan or air conditioning may somewhat reduce the temperature and increase comfort. If the temperature reaches the extremely high level of hyperpyrexia, aggressive cooling is required.
Medications and treatment:
Generally, if the fever does not cause discomfort, the fever itself need not be treated. It is not necessary to awaken an adult or child to treat a fever unless instructed to do so by your health-care practitioner.
The antipyretic ibuprofen is effective in reducing fevers in children. It is more effective than acetaminophen (paracetamol) in children. Ibuprofen and acetaminophen may be safely used together in children with fevers. The efficacy of acetaminophen by itself in children with fevers has been questioned. Ibuprofen is also superior to aspirin in children with fevers. Additionally, aspirin is not recommended in children and young adults (those under the age of 16 or 19 depending on the country) due to the risk of Reye's syndrome.
Fever phobia is the name given by medical experts to parents' misconceptions about fever in their children. Among them, many parents incorrectly believe that fever is a disease rather than a medical sign, that even low fevers are harmful, and that any temperature even briefly or slightly above the oversimplified "normal" number marked on a thermometer is a clinically significant fever. They are also afraid of harmless side effects like febrile seizures and dramatically overestimate the likelihood of permanent damage from typical fevers.
As a result of these misconceptions, parents are anxious, give the child fever-reducing medicine when the temperature is technically normal or only slightly elevated, and interfere with the child's sleep to give the child more medicine. Fever of 104°F (40°C) or higher demand immediate home treatment and subsequent medical attention, as they can result in delirium and convulsions, particularly in infants and children.
How to take a temperature for fever?
Digital thermometers can be used to measure rectal, oral, or axillary (under the armpit) temperatures. The American Academy of Pediatrics does not recommend use of mercury thermometers (glass), and they encourage parents to remove mercury thermometers from their households to prevent accidental exposure to this toxin.
Axillary temperatures are not as accurate as rectal or oral measurements, and these generally measure 1 degree lower than a simultaneously obtained oral temperature. Place the tip of the digital thermometer in your child's armpit. Leave in place about one minute or until you hear a beep to check a digital reading.
Tympanic (ear) thermometers must be placed correctly in your child's ear to be accurate. Too much earwax can cause the reading to be incorrect. Eardrum temperature measurements are not accurate in small children and should not be used in children under 3 years (36 months) of age. This is especially true in infants below 3 months of age when obtaining an accurate temperature is very important.
People 4 years old and older can have their temperature taken with a digital thermometer under the tongue with their mouth closed. Clean the thermometer with soapy water or rubbing alcohol and rinse. Turn the thermometer on and place the tip of the thermometer as far back under the tongue as possible. The mouth should remain closed, as an open mouth can cause readings to be inaccurate. The thermometer should remain in place for about one minute or until you hear the beep. Check the digital reading. Avoid hot or cold drinks within 15 minutes of oral temperature measurement to ensure correct readings.
The American Academy of Pediatrics recommends rectal temperature measurements for children under 3 years of age, as this gives the most accurate reading of core temperature. Clean the thermometer with soapy water or rubbing alcohol and rinse with cool water. Use a small amount of lubricant, such as petroleum jelly, on the end. Place the child prone (belly-side down) on a firm surface, or place your child face up and bend his legs to his chest. After separating the buttocks, insert the thermometer approximately ½ to 1 inch into the rectum. Do not insert it too far. Hold the thermometer in place, loosely keeping your hand cupped around your child's bottom, and keep your fingers on the thermometer to avoid it accidently sliding further into the rectum. Keep it there for about one minute, until you hear the beep. Remove the thermometer, and check the digital reading. Label the rectal thermometer so it's not accidentally used in the mouth. A rectal temperature will read approximately 1 degree higher than a simultaneously obtained oral temperature.
Any child below 3 months of age who has a temperature of 100.4 F (38 C) or greater should be seen by a physician or other health-care worker. If a child or adult has a history or diagnosis of cancer, AIDS, or other serious illness, such as heart disease, diabetes, or is taking immunosuppressant drugs, medical care should be sought for a fever.
Otherwise, observe the person with the fever. If they appear sick or have symptoms that would suggest a major illness, such as meningitis (headache, stiff neck, confusion, problems staying awake), urinary tract infection (shaking chills, burning with urination), pneumonia (shortness of breath, cough), or any other signs of a serious illness, contact your health-care provider.
Other symptoms that may be indicative of a severe illness include repeated vomiting, severe diarrhea, or skin rashes (could be a sign of dengue fever, Rocky Mountain spotted fever, scarlet fever, rheumatic fever, or chickenpox).
Fever blisters (herpangina) are small blisters that turn into ulcers, usually on the lips, mouth or tongue that are caused by a virus. When a child contracts this virus for the first time, the symptoms and the fever blisters can be quite severe. If the child is not eating or drinking, contact your child's health-care provider.
Some vaccines given in childhood can cause a low-grade fever within a day or two of getting the injection. This fever is usually self-limited and short-lived. If the reaction seems severe or the skin at the injection site is red, hot, and painful, contact your child's doctor.
About 3% of all children between 18 months to 3 years of age will have a seizure (convulsion) with a high fever. Of those with a history of febrile seizure, approximately one-third will have another seizure associated with another febrile episode. Febrile seizures, while frightening to the parents, are not associated with long-term nervous-system side effects. Children used to be prescribed Phenobarbital following a febrile seizure as a preventive measure (prophylaxis). This has not been shown to be beneficial and possibly may be harmful, so it is not always recommended.
Children may have a low-grade fever for 1 or 2 days after some immunizations. Teething may cause a slight increase in a child's temperature, but not higher than 100 °F.
The illness is probably not serious if your child:
•Is still interested in playing
•Is eating and drinking well
•Is alert and smiling at you?
•Has a normal skin color
•Looks well when their temperature comes down
Take steps to lower a fever if you or your child is uncomfortable, vomiting, dried out (dehydrated), or not sleeping well. Remember, the goal is to lower, not eliminate, the fever.
When trying to lower a fever:
•Do NOT bundle up someone who has the chills.
•Remove excess clothing or blankets. The room should be comfortable, not too hot or cool. Try one layer of lightweight clothing, and one lightweight blanket for sleep. If the room is hot or stuffy, a fan may help.
•A lukewarm bath or sponge bath may help cool someone with a fever. This is especially effective after medication is given -- otherwise the temperature might bounce right back up.
•Do NOT use cold baths, ice, or alcohol rubs. These cool the skin, but often make the situation worse by causing shivering, which raises the core body temperature.
How to prevent fever?
Hygiene - fevers are commonly caused by bacterial/viral infections. Good hygiene practices help reduces the risk of developing an infection. This includes handwashing before and after meals, and after going to the toilet.
A person with fever caused by an infection should have as little contact as possible with other people, to prevent the infection from spreading. Whoever is caring for the patient should regularly wash their hands with warm soap and water.
Certain people who work with animals can be exposed to rare bacteria that can cause fevers. In addition to the fever, the person may have chills, headache, and muscle and joint aches. These bacteria can exist in livestock, in unpasteurized dairy products, and in the urine of infected animals.
Anyone who travels, especially outside the hometown, may develop fever after exposure to various new foods, toxins, insects, or vaccine-preventable diseases.
Insect bites are a common way that infections are spread in some countries. Malaria is a serious infection that can occur after a mosquito bite. The bitten person may have fevers that come and go every few days. A blood test must be done to make the diagnosis. In certain infected areas, a traveler can take medication to prevent malaria.
Occasionally a blood clot can develop in a person's leg and cause swelling and pain in the calf. Part of this clot may break off and travel to the lungs. This may cause chest pain and trouble breathing. In either case, a person may develop a fever because of inflammation in the blood vessels. A person with any of these symptoms should go to the hospital.
