What Is Fever (Pyrexia)? What Causes Fever?

Fever, pyrexia or controlled hyperthermia is when a human's body temperature goes above the normal range of 36-37C (98-100F) - it is a common medical sign. As the individual's body temperature goes up, there may be a sensation of cold until the temperature plateaus (stops rising).

An elevated body temperature (fever) is one of the ways our immune system attempts to combat an infection. Usually the rise in body temperature helps the individual resolve an infection. However, sometimes it may rise too high, in which case the fever can be serious and lead to complications.

Doctors say that as long as the fever is mild, we do not generally need to try and bring it down - if the fever is not severe it is probably having an effect in neutralizing the bacterium or virus that is causing the infection. Medications to bring down a fever are called antipyretics. If the fever is causing undue discomfort, an antipyretic may be recommended. US and UK doctors say that when the fever reaches or exceeds 39.4C it is no longer mild.

According to Medilexicon's medical dictionary:

Fever is: A complex physiologic response to disease mediated by pyrogenic cytokines and characterized by a rise in core temperature, generation of acute phase reactants, and activation of immune systems.

What are the signs and symptoms of fever?

A symptom is something the patient reports and feels, while a sign is something other people, including a doctor may detect. For example, a headache may be a symptom while a rash may be a sign.

When somebody has a fever, signs and symptoms are linked to what is known as sickness behavior, and may include:

• Feeling cold when nobody else does
• Shivering
• Anorexia - lack of appetite
• Dehydration - preventable if the patient drinks plenty of fluids
• Depression
• Hyperalgesia - the individual is much more sensitive to pain
• Lethargy
• Problems concentrating
• Sleepiness
• Sweating

If the fever is high there may also be extreme irritability, confusion, delirium and convulsions.

Febrile seizure (children)

Children with a high temperature may develop a febrile seizure, also known as a febrile fit or febrile convulsion, most of which are not serious and may be the result of an ear infection, gastroenteritis, or a respiratory virus (a cold). Less commonly, febrile seizures may be caused by something more serious, such a meningitis, a kidney infection or pneumonia.

Febrile seizures most commonly occur in children aged 6 months to 6 years, and affect boys more often than girls.

The seizure occurs because the body temperature rises too fast, rather than because it has been sustained for a long time.

There are two types of febrile seizures:

• Simple febrile seizure - the seizure lasts no longer than 15 minutes (in most cases less than 5 minutes) and does not occur again during a 24-hour period.
  
  It typically involves the whole body - a generalized tonic-clonic seizure. Most febrile seizures are of this type. Symptoms - the body becomes stiff and the arms and legs start to twitch, the patient loses consciousness (but the eyes stay open).
  
  There may be irregular breathing and the child may urinate and/or defecate. There may also be vomiting.


• Complex febrile seizure - the seizure lasts longer, comes back more often, and tends not to affect the whole body, but rather only part of the body.
  
  This type of seizure is a cause for more concern that simple febrile seizures.

In the majority of cases, a child with a febrile seizure does not need treatment. Temperature may be controlled with acetaminophen (paracetamol) or sponging. If necessary an anticonvulsant, such as sodium valproate or clonazepam may be prescribed.

What are the causes of fever?

• An infection - such as strep throat, flu, chickenpox or pneumonia
• Rheumatoid arthritis
• Some medications
• Over-exposure of skin to sunlight (sunburn)
• Heat stroke - may be caused either by exposure to high temperatures (nonexertional heat stroke) or prolonged strenuous exercise.
• Silicosis - a type of lung disease caused by long-term exposure to silica dust.
• Amphetamine abuse
• Alcohol withdrawal

How is fever diagnosed?

Diagnosing a fever is straightforward - the patient's temperature is taken, if the reading is high, he/she has a fever. It is important to take the person's temperature when they are at rest, because physical activity can warm us up.

A person is said to have a fever if:

• The temperature in the mouth is over 37.7C (99.9F)
• The temperature in the rectum (anus) is over 37.5-38.3C (100-101F)
• The temperature under the arm or ear is over 37.2C (99F)

As a fever is a sign rather than a disease, when the doctor has confirmed there is an elevated body temperature, certain diagnostic tests may be ordered, depending on what other signs and symptoms exist, these may include blood tests, urine tests, x-rays and other imaging scans.

What is the treatment for fever?

NSAIDs (non-steroidal anti-inflammatory drugs) such as Tylenol (paracetamol) or ibuprofen can help bring a fever down. However, a mild fever may be helping combat the source of the infection (bacterium/virus) - it may not be ideal to bring it down.

If the fever has been caused by a bacterial infection the doctor may prescribe an antibiotic.

If a fever has been caused by a cold, which is caused by a viral infection, NSAID's may be used to relieve uncomfortable symptoms. Antibiotics have no effect against viruses, but may sometimes be prescribed to prevent secondary infections.

Fluid intake - the patient with a fever should consume plenty of fluids (liquids) to prevent dehydration.

Heat stroke - NSAIDs will not be effective if the person's fever was caused by hot weather or sustained strenuous exercise. The patient needs to be cooled. If they are confused or unconscious they should be treated by a doctor straight away.

How to prevent fever?

Hygiene - fevers are commonly caused by bacterial/viral infections. Good hygiene practices help reduce the risk of developing an infection. This includes hand washing before and after meals, and after going to the toilet.

A person with a 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.