Fever Unveiled: What Your Temperature Tells You

What is fever?

We, along with other mammals, maintain body temperature through tightly controlled, self-regulatory mechanisms which are independent of external temperatures³.  Yet it is normal for body temperature to vary by approximately 0,5 to 1 degree Celsius throughout the course of the day as many normal bodily processes may affect it. These include sleep/wake cycles, changes in metabolism, and changes in hormone levels, while physical activity (or lack thereof) may also influence it^2,4.

During a normal day, body temperature is usually lowest at about 6 am and at its highest at 4 to 6 pm⁴.

When the body temperature rises to 38 degrees Celsius or above, it is inevitably regarded as a sure sign of an underlying disease¹.

Most people experience fever at some point. It can last from a couple of hours to multiple days, depending on the underlying cause. Healthcare workers rely on fever as a “vital sign” to alert them that their intervention may be called for⁵.

Measuring body temperature

Measuring body temperature may not be as straightforward as it may seem, as different body parts have different temperatures. There are also different thermometers (i.e., any device used to measure temperature) with different levels of accuracy. The most common sites of temperature measurement include⁴:

The mouth

Body temperature is frequently measured with the use of glass thermometers containing a liquid such as mercury that is placed underneath the tongue. This area responds promptly to changes in core temperature because of its blood supply. While the mouth is the most easily accessible site, it does require patient cooperation and may not always be suitable to measure temperature in young children or uncooperative adults. It may also be influenced by the ingestion of hot or cold food or smoking before measurement.

The rectum

Although the rectum is very frequently used to obtain temperature measurements, at least 3 minutes is required to obtain accurate readings with thermometers containing mercury. It also carries a small risk of rectal perforation, especially in newborns and very young infants. It has been reported that the accuracy of rectal temperature measurement is poor at extremes of temperature because it is slow to reflect change.

The axilla (“armpit”)

While the axilla provides a reasonable approximation of body temperature in the newborn, it is less so for the older child or adult. The main problem is the long dwell time to obtain accurate measurements with 9 minutes required for thermometers containing mercury. It may not be very accurate if used outside of the hospital setting.

The ear canal

Infrared tympanic membrane thermometers are used for measuring core body temperature, because of the good blood supply to the tympanic membrane (“eardrum”). These thermometers work like cameras as they detect infrared energy emitted from the tympanic membrane and portions of the ear canal. The thermometer then processes the information and displays a value that represents either the tissue temperature in the ear canal or an adjusted estimate of the temperature in other sites. Advantages of tympanic membrane thermometers include being a non-contact instrument and the short dwell time (less than a few seconds), but they are unfortunately expensive, and there have also been conflicting reports of accuracy as compared with other thermometers.

Causes

Fevers may arise from external (exogenous) or internal (endogenous) causes⁴:

• Exogenous causes include cell membranes of germs such as bacteria or toxins produced by such bacteria as well as viruses, medicines, or vaccinations (leading to the production of antigen-antibody complexes).
• Endogenous causes are illnesses or diseases that produce certain hormones or enzymes that disturb the body’s thermoregulatory balance. Examples include auto-immune diseases or certain cancers.

Benign viral infections are the most common causes of fevers. Serious, less frequent causes of fever include bacterial infections leading to meningitis, pneumonia, or septicaemia⁷.

Diagnosis

While it is important to never underestimate the perception that someone is warm to the touch, it is also known that the “back-of-the-hand” technique may overestimate fever⁶.

It is therefore important to measure temperature with one of the techniques mentioned above. In general, an abnormally increased body temperature can be defined as more than:

• 37,5 degrees Celsius if measured orally
• 38 degrees Celsius if measured rectally
• 37,2 degrees Celsius if measured in the axilla^4,6
• 37,9 degrees Celsius for children younger than 11 years and 37,6 degrees Celsius for individuals aged 11 years and older in case of tympanic membrane measurements⁴.

When to see a doctor

It is important to remember that fever is not a disease, but rather the body’s response to an underlying illness¹.

Fever often occurs because of an infection, and it has been shown to decrease the rates at which germs such as bacteria or viruses grow or multiply. In such instances, fever thus serves a protective role⁴. On the other hand, people with fever feel poorly and may experience fatigue, joint pain, muscle pain, loss of appetite, and sometimes may become confused. Fever may also cause a rapid heart rate, rapid breathing and, in children, carries a risk of febrile convulsions⁶.

A mild fever with no other symptoms is generally not a cause for concern and should not be treated^6,7. To help one make the decision about whether or not to see a doctor, the following three questions may be helpful^6,8:

How old is the person?

Babies under 3 months of age with high fevers (equal to or above 38 degrees Celsius) are at risk of serious bacterial infections and should always be taken to a doctor for evaluation. The same holds true for babies between 3 and 6 months of age with a temperature equal to or above 39 degrees Celsius.

How sick is the person?

The following serious signs in children should best be evaluated by a doctor: lethargy (characterised by poor eye contact or failure to recognise parents), pallor, or blue discolouration of the skin. A mottled or ashen skin colour also warrants further evaluation. Other symptoms and signs of concern are lack of response to social cues, does not wake or if roused does not stay awake, weak or high-pitched or continuous crying, grunting, very rapid breathing, and neck stiffness. Poor feeding in infants and reduced urine output in adults and children are also indicative of a need for medical attention.

How long has the person been sick?

The longer a fever lasts, the greater the likelihood that there is a serious underlying problem. Most self-limiting illnesses last fewer than 5 days.

Treatment

A mild fever with no other symptoms generally does not require treatment^6,7.

Fever is not dangerous in itself and fever will not damage a child’s brain or harm a child’s development⁶.

It is generally recommended that parents administered a fever-lowering medication (i.e., an antipyretic) when a child with fever appears distressed. The aim should be on comforting the child rather than on achieving a normal temperature. Recommended antipyretics for children include paracetamol and ibuprofen⁸. The dose of the medicine should be based on the child’s weight rather than age⁹. If uncertain, it is best to consult with your pharmacist.

Physical treatment of fever includes rest in a well-ventilated room. Additional measures include:

Fluids

To avoid dehydration, it is important to keep in mind that there is a 12 % increase in fluid requirements for every 1 degree rise in body temperature⁴.

Body sponging

This should be done with a lukewarm, water-soaked towel, if required⁴, although newer guidelines in the United Kingdom no longer recommend tepid sponging⁸.

Light clothing

The person should not be underdressed or over-wrapped⁸.

The don’ts when someone has a fever:

• Do not sponge them with alcohol. It can be absorbed through the skin⁴.
• Do not put a fan on them¹⁰.
• Do not administer aspirin to children because of the risk of Reye’s syndrome (a rare, but potentially life-threatening condition)⁴.
• Do not combine or alternate antipyretic medicines in children⁹ unless it is to address symptoms other than fever (for example, pain or swelling resulting from inflammation).

Fever complications

Febrile seizures

Some children between the ages of six months and six years old get seizures triggered by fever.  Such febrile seizures are the most common type of convulsions in children. While they may be nerve-racking, these seizures usually only last a few minutes and are generally harmless^11,12. They occur in healthy children who have normal development and who did not have neurological symptoms previously¹².

Typical signs and symptoms of febrile seizures include¹¹:

• Loss of consciousness
• Difficulty breathing
• Looking pale or turning blue
• Foaming at the mouth
• Eyes rolling to the back of the head or a fixed gaze
• Generalised (whole-body) or focal (localised) twitching
• Jerking of the arms and legs.

Children usually recover completely from a febrile seizure after approximately 30 minutes; however, they may be irritable, confused, or drowsy in the immediate aftermath. Approximately 70 % of febrile seizures are so-called simple febrile seizures which generally have no long-term consequences. These seizures are characterised by whole-body tonic-clonic seizures that last less than 10 minutes, and which resolve spontaneously. There is no recurrence within 24 hours. The other 30 % is made up of complex febrile seizures.

These seizures have focal/localised features in which, for example, only one side of the body is involved, last more than 10 minutes, and may recur within a 24-hour period. Full recovery is not observed after one hour and there may be neurological consequences following the seizure. Some children may experience a short period of paralysis (defined as Todd’s paralysis). A further possible complication of complex febrile seizures is the development of Febrile Status Epilepticus where the seizure lasts for more than 20 minutes and where the use of anticonvulsant medication is required to interrupt it^11,13.

If your child has a febrile seizure:

• Gently place your child on the floor or ground^14.
• Remove any nearby objects¹⁴.
• Place your child on his/her side to prevent choking¹⁴.
• Loosen any clothing around the head or neck¹⁴.
• Follow the ABC protocol: Make sure the airway is clear, that the child is breathing and feel the pulse to check circulation^13,14.
• Call the ambulance if the seizure is accompanied by vomiting, a stiff neck, breathing problems or extreme sleepiness¹².
• Call the ambulance if the seizure lasts longer than 5 minutes or your child turns blue^13,14.

It is important to remember that most febrile seizures produce no lasting effects.

Simple febrile seizures will not lead to brain damage, intellectual disability, or learning disabilities. They are also not indicative of a more serious underlying disorder¹².

The most common complication of a febrile seizure is recurring seizures. Your child’s risk of developing recurring seizures is higher if:

• The first seizure resulted from a low-grade fever.
• The febrile seizure was the first sign of illness.
• An immediate family has a history of febrile seizures.
• Your child was younger than 18 months at the time of the first febrile seizure¹².

Unlike epilepsy, prescription anticonvulsant medicines are rarely used to prevent febrile seizures¹² and their routine use is not recommended¹³. These seizures have an excellent prognosis¹³.