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A body temperature of more than 37.2C or 98.9F in the morning or a temperature of more than 37.7 or 99.9F in the evening indicates fever.

Fever is a symptom that has plagued each of us at some time or the other. Often, people try to treat fever at home. A better understanding about fever will no doubt help in managing fever better at home; it will also ensure that a doctor is consulted at the right time.

Man is a warm-blooded animal, that is, body temperature is maintained regardless of the environmental temperature. The normal temperature of the body is maintained at 37C or 98.6F by the hypothalamus, a small but important part situated just below the brain. A slight variation of 0.5C or 0.9F occurs during the day.

Fever is defined as a before-noon temperature of more than 37.2C or 98.9F or an after-noon temperature of more than 37.7C or 99.9F. Fever is an elevation in normal body temperature that occurs in connection with a raised hypothalamic set point.

Body temperature is measured using a thermometer. The reading is obtained either by placing a thermometer in the mouth, in the rectum (especially in children), from the ear near the ear drum or in the armpit. Rectal temperatures are usually 0.5C or 0.7F higher than oral temperatures. Temperatures taken in the armpit are usually not very reliable.

Very high temperature of more than 41.5C or 106.7F is called hyperpyrexia. It occurs due to brain hemorrhage or severe infections.

Some causes of fever are listed below:

► Infections: Viral, bacterial, fungal or protozoal infections often cause fever. Some additional features that can help in the diagnosis of fever due to infections are:

► Fever of short duration without specific symptoms may be due to influenza

► Fever with throat pain and difficulty in swallowing could be due to sore throat infection, diphtheria or infectious mononucleosis (infection by a virus called Epstein-Barr virus)

► Fever with cough, chest pain and rusty sputum may be due to pneumonia

► Fever with rigors and burning while passing urine indicates a urinary tract infection

► An alternate day fever with rigors indicates malarial infection

► Fever with swelling of feet with rigors and a raised eosinophil count may indicate filariasis

► An increasing fever with pain in abdomen, small red spots on the skin and a slow heart rate could be due to typhoid

► Fever with neck stiffness, headache and vomiting may be due to meningeal infection (infection of the covering of the brain)

► Fever with cough over a long duration and weight loss may indicate tuberculosis

► Fever with rashes may be due to a viral infection

► Short-duration fever with progressive weight loss and a high-risk behavior could possibly be due to HIV infection

► Drugs and Biological Agents: Drugs like beta-lactam antibiotics, procainamide, isoniazid, alpha-methyldopa, quinidine and diphenylhydantoin are associated with fever. Biological agents like interferons and interleukins used in therapy could also cause fever. Vaccines could also result a temporary rise in temperature. Fever caused by drugs is often associated with a rash.

► Tissue injury: Heart attack, burns, trauma and injections into muscles damage tissues and can cause fever.

► Cancers: Blood cancers like leukemia and lymphoma, and liver cancer can cause fever. The liver, spleen and lymph nodes may be enlarged and easily felt in these conditions.

► Inflammatory diseases: Rheumatoid arthritis, systemic lupus erythematosus and inflammatory bowel disease are some inflammatory diseases that could cause a rise in body temperature.

► Hormonal diseases: Thyrotoxicosis (a condition in which the thyroid gland is hyperactive) and pheochromocytoma (a condition in which the adrenal gland is affected) can cause fever.

Metabolic diseases: Gout and increase in blood urea can sometimes raise the body temperature.

► Genetic diseases: Familial Mediterranean fever is a genetic disease with fever as one of its symptoms.


The cause of fever can be diagnosed from the pattern and associated features.

The pattern of fever may vary in different conditions and could assist in the diagnosis of the cause of the fever. Some of the types of fever are listed below:

Continuous fever: Fever that does not fluctuate more than 1C in 24 hours is called continuous fever. It is seen in conditions like pneumonia, typhoid, urinary tract infections and infective endocarditis.

Remittent fever: Fever that fluctuates more than 1C in 24 hours is referred to as remittent fever. Causes include typhoid and infectious mononucleosis.

Intermittent fever: Fever that is present only for some time in the day is called intermittent fever. Malaria caused by Plasmodium vivax results in fever every third day and that caused by Plasmodium malariae results in fever every fourth day.

Hectic or septic fever: Fever variation between the highest and lowest temperatures is very large and more than 5C. This type of fever is seen in septicemia or infection of the blood

Pel Ebstein fever: The febrile and afebrile periods alternate and follow a definite pattern. For example, in Hodgkins disease and other lymphomas, fever for 3 to 10 days is followed by a fever-free period of 3 to 10 days, with the same cycle repeating.

Low-grade fever: The fever does not exceed 37.8C and is present daily especially in the evenings. Tuberculosis causes low-grade fever.

Fever with rigors: Rigor is the shaking or excessive shivering that accompanies fever. Fever accompanied with rigors are seen in conditions like malaria, kala azar, filariasis, urinary tract infections, inflammation of gall bladder, septicemia, infective endocarditis or inflammation of the inner layer of the heart, abscesses and pneumonia.

Fever with herpes labialis: Fever sometimes results in activation of herpes simplex virus. This results in small fluid-filled boils at the angles of the mouth. Fever with herpes labialis is seen in pneumonia, malaria, meningitis and severe infection with streptococci.

Fever with rash: Fever with rash is often seen in viral infections like chicken pox, small pox, measles and rubella or German measles. Other conditions like typhus and allergy also result in fever with rash.

Fever with membrane in throat: Febrile conditions that could result in the formation of a membrane in the throat include diphtheria, infectious mononucleosis, agranulocytosis (a condition where white blood cell count is low), fungal infection and Vincents angina or trench mouth.

Fever with delirium or altered consciousness: Delirium with fever could occur in conditions like encephalitis or infection of the brain, typhoid, meningitis, pneumonia or severe liver disease.

Frequently Asked Questions

1. Which doctor should I visit for fever?

You should visit your family doctor in case of fever. He may refer you to a specialist if required.

2. How is fever treated?

Fever is a symptom and not a disease by itself. Thus, the most important approach in the treatment of fever is to identify the underlying cause and treat it. In some cases like some viral infections, the fever may be self-limiting, that is, the fever will disappear once the infection is cleared.

Fever may be brought down using drugs belonging to the group antipyretics. Among these, acetaminophen (or paracetamol as it is referred to in some countries) is a safe and effective treatment for fever. Aspirin may be used in adults but should be avoided in children. Other drugs like ibuprofen and diclofenac can also be used instead of acetaminophen.

3. What is fever of unknown origin (FUO)?

Fever of unknown origin (FUO) was defined as fever with a temperature of more 101F on several occasions, lasting more than 3 weeks, which includes a hospital stay of more than 1 week with a failure to diagnose the cause by Petersdorf and Beeson in 1961.

Durack and Street proposed a revised system of classification of FUO. Accordingly, FUO includes:

1) Classic FUO

2) Nosocomial FUO

3) Neutropenic FUO

4) FUO associated with HIV infection

The earlier definition corresponds closely to the current definition of classic FUO.

Some of the causes include conditions like lymphoma, tuberculosis, viral infections, hospital acquired conditions, fungal infections and infections in HIV patients.

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