Fever is a condition where the body temperature goes above the normal range. The normal range is 36–37° Centigrade or 98–100° Fahrenheit).
Fever is a very common symptom occurring due to infection, inflammation or other body conditions releasing pyrogens.
Pyrexia is another term for it.
Body’s core temperature is controlled by anterior hypothalamus. Pyrogens released in the body set this core temperature to a higher level and cause body temperature to rise [similar to raising the temperature on the thermostat.]
This is in contrast to hyperthermia where the body temperature rises without a change in the heat control centers.
The rise in temperature of the body causes an unpleasant sensation.
How does Fever Occur?
The body temperature refers to the temperature of the viscera and tissues of the body. It is kept within the normal level by maintaining a balance between the heat gain and heat loss, which is regulated by the hypothalamus.
Normal body temperature is affected by various factors like diet, exercise, and sleep.
There is a diurnal variation of the temperature too. The temperature is highest in the evening and lowest in late night/early morning hours.
A rise in body temperature is body’s defence against infections and other insults carried out by release of pyrogens which act on the temperature regulation centers. It helps in curbing bacteriae or virus.
But a very high rise in temperature can be dangerous and lead to complications.
In fact, it is not recommended to bring mild fevers down in case of infections. But a high fever needs to be controlled with antipyretic drugs and other measures.
Fever or pyrexia is an increase of more than 1 degree Celsius or any rise above the maximal normal temperature.
Fever makes you feel sick. Fever itself is a symptom but when it occurs, there are other symptoms which one may feel.
Not all the patients feel all the symptoms.
- feeling cold with or without shivering
- decrease in appetite
A high fever can cause irritability, confusion, delirium, and seizures.
Classification of Fever
A fever can be:
- low grade, from or 38.1–39°C
- moderate, from or 39.1–40°C
- high, from to or 40.1-41.1°C
- hyperpyrexia, above 106.0°F or 41.1°C
A fever lasting less than 7 days is called acute, <14 days subacute and chronic if occurs for more than 14 days.
How to Measure Temperature
Fever can be measured by thermometer. There are various types of thermometers that can be used for measurement of temperature. Oral and armpits are the places where most of thermometers are used.
The body temperature is best recorded with a mercury thermometer which should be kept in position for about a minute. Usually, the temperature is recorded in the axilla.
What are Different Types of Fever
It must be noted that the following types of fever association are generally noted as classic associations and overlap might occur.
The temperature remains above normal throughout the day and does not fluctuate more than 1 degree Celsius in 24 hours. This type of fever occurs in lobar pneumonia, typhoid, urinary tract infection, infective endocarditis, brucellosis, typhus etc.
The temperature remains above normal throughout the day and fluctuates more than 2 degree Celsius in 24 hours. This type of fever is usually seen in patients of typhoid infection and infective endocarditis. This type of fever is most commonly seen.
The high temperature is present only for some hours in a day and returns to normal for the remaining hours. When the spike occurs daily, it is quotidian; when every alternate day, it is tertian; and when every third day, it is quartan. Intermittent fever is seen in malaria, kala-azar, pyemia, septicemia, etc.
Hectic or Septic Fever
The temperature variation between peak and nadir is very large and exceeds 5 degree Celsius. This type of fever occurs in septicemia.
Pel Ebstein Fever
In this type, there is a regular alternation of recurrent bouts of fever and afebrile periods. The temperature may take 3 days to rise, remains high for 3 days and remits in 3 days, followed by apyrexia for 9 days.
Temperature is present daily especially in the evening for several days but does not exceed 37.8 degree Celsius at any time. Usually, it does not indicate disease, but it is commonly associated with tuberculosis.
Step – Ladder Fever
The stepladder is the one where the temperature rises gradually to a higher level with every spike so that new plateau is higher than preceding one, just like steps of the ladder.
Febrile episodes are separated by intervals of normal temperature. Fever, when occurs, may last for 2-9 days and then temperature gets normal. The fever may relapse after a period of few days repeating the same cycle.
It is typically seen in Borrelia infections.
Fever occurs once in 3 days or 48 hours (malaria).
Fever occurs once in four days or 72 hours (malaria due to Plasmodium malariae).
The patient gets two spikes of fever every day, generally once in the morning and once in the evening. Double quotidian may be a feature of miliary tuberculosis.
The temperature rises in the early hours of the morning rather than in the evening. It is also seen in some cases of miliary tuberculosis.
A rise in body temperature is evident in the evening hours or the patient may be woken up at night with sweating. Tuberculosis, leukemias, autoimmune disorders may have this fever.
Causes of Fever
Fever may occur whenever pyrogens are released into the body.
Any infection whether bacterial, viral, rickettsial, fungal or parasitic can give rise to fever.
Hypernephroma, lymphoproliferative malignancies, carcinoma of pancreas, lung and bone and hepatoma may cause fever.
Acute myocardial infarction, pulmonary embolism, pontine hemorrhage may also cause fever.
A massive crush injury may lead to pyrexia.
Diseases like collagen disorders, systemic lupus erythematosus, rheumatoid arthritis, etc can lead to an increase in body temperature. Drug fever and serum sickness are can also cause fever.
Thyrotoxicosis and Addison’s disease may raise body temperature.
Fever may occur in metabolic diseases like Gout, porphyria, acidosis, dehydration, hematological conditions like an acute hemolytic crisis. Heat stroke and radiation sickness can be accompanied by fever.
Special Types of Fever
Fever with Rigors
This occurs in:
- Kala azar
- Urinary tract infection
- Infective endocarditis
Fever with Herpes Labialis
Elevated body temperature may activate the herpes simplex virus and cause small vesicles around the angle of the mouth (herpes labialis). It occurs with:
- Streptococcal infection
Fever with Rash
This is seen in:
- Chicken pox
- Small pox
Fever with Throat Membrane
- Infectious mononucleosis
- Vincent’s angina
Fever with Delirium
This is common in:
- Typhoid state
- Pneumonia (especially in alcoholics and elderly people with senility)
Non-steroidal anti-inflammatory drugs are the medications given to bring the temperature down.
Paracetamol is the most common antipyretic drug used. But it should be used with restraint especially in children.
In fact, mild fever need not be brought down as it is beneficial for the body.
In the case of bacterial infections, antibiotics may be prescribed.
Plenty of fluid should be consumed as fever is a state of high temperature and the body loses a lot of water.
Complications of Fever
Fever usually responds to medications or follows a self-limiting course. It induces a state of catabolism which is detrimental to the body. It may also lead to fluid and electrolyte imbalance-due to sweating and loss of minerals. High-grade fevers can lead to convulsions, brain damage, circulatory overload, and arrhythmia.
A high temperature in children can lead to seizures.
Hyperpyrexia is said to occur when body temperature is more than 105 degrees Fahrenheit. It usually occurs in the following conditions
- Heat Stroke
- Pontine hemorrhage