1 Fever Summary

Fever or high body temperature is not a disease in itself, but a symptom of an underlying condition like an infection. Body temperature above 98.6˚F, the normal temperature, is usually considered as fever.

It is significant only when it goes above 100.4 ˚F. Fever normally causes physical discomfort that affects the daily activities to a certain extent. Treatment depends on the underlying cause, age, and physical condition of the person.

It is generally considered that fever is a defense system of the body against infection. But, fever may be caused by some non-infectious reasons also.

The body may respond to foreign objects like viruses, bacteria, toxins and drugs by increasing the body temperature. But, normal body temperature may vary slightly in different individuals.

It may also vary according to the time of the day. It is generally higher during the late afternoon. Body temperature is also affected by menstrual cycle in women and intense physical activity.

Symptoms of fever depend on the underlying cause of the increase in temperature. Other symptoms usually associated with fever include sweating, headache, muscle pain, shivering or chills, lack of appetite, dehydration, and weakness.

Higher temperatures like 103 ˚F - 106˚F cause other symptoms including hallucinations, irritability, confusion, dehydration, and convulsions.

An increase in body temperature is of concern in infants and children when: 

  • Rectal temperature is higher than 100.4˚F in infants
  • The temperature goes above 102˚F and the child becomes irritable or uncomfortable
  • High fever (temperature >102˚F) persists for more than a day without any other symptoms.
  • High fever with associated symptoms like cold, cough or diarrhea

In children above 2 years of age, fever is of concern if the child is listless and does not respond to your expressions. It requires immediate attention if high fever is accompanied by repeated vomiting and poor eye contact.

In adults, fever is of concern if the temperature goes above 103˚F and persists for more than three days at a stretch.

Medical attention is required if the fever is accompanied by certain signs and symptoms like:

  • Swelling in throat
  • Skin rashes that worsens over time
  • Sensitivity to bright light
  • Stiffness of neck
  • Confusion
  • Vomiting
  • Breathlessness
  • Chest pain
  • Irritability
  • Abdominal pain
  • Pain during urination
  • Muscle weakness
  • Seizure

Fever is caused by a number of factors including infection, sunburn, heat exhaustion, inflammatory conditions, some medications and certain immunizations. If not treated, fever may lead to complications like dehydration, hallucinations, and seizures.

Diagnosis of fever and the underlying cause is based on signs and symptoms and physical examination. Tests and examinations are recommended based on the probable cause of the increase in temperature.

No specific treatment is required for a low-grade fever. Over-the-counter medications and prescription medications are suggested for bringing down the body temperature.

Hospitalization is usually recommended for infants younger than a month, particularly for tests and treatment. This will help in continuous monitoring and to give intravenous medications.

Drinking plenty of fluid is one of the most popular home remedies for controlling fever. A person with a high fever needs adequate rest. Many types of fever can be prevented by following good hygienic practices.

2 Causes

The hypothalamus, also known as the thermostat of the body, plays an important role in regulating body temperature. During fever, the set point of the body temperature at a higher scale.

This often results in chills and shivers, both of which help in increasing the temperature. Foreign substances like bacteria, virus, fungus or toxins are considered to be pyrogens or fever-producing substances.

Pyrogens trigger the immune response for launching an appropriate defense mechanism against the invaders. It is these pyrogens that signal the hypothalamus to set the body temperature high so as to fight the infection.

Under normal conditions, the body temperature is set at 98.6˚F, which may vary slightly in different people. It may range from 97˚F to 99˚F.

Number of factors are known to trigger fever, like:

  • Infections like flu, pneumonia, chicken pox or common cold
  • Teething in infants
  • Some inflammatory conditions like rheumatoid arthritis and Crohn’s disease
  • Sunburn by over exposure to sunlight
  • Heat exhaustion caused by exposure to high temperature or prolonged intense physical activity like exercise. Both the conditions overheat the body and result in hyperthermia. It is a medical emergency and the affected person must be cooled as soon as possible.
  • Blood clots developed in the leg sometimes break off and move towards heart and lungs. Inflammation of the blood vessels, in this case, results in fever.
  • Food poisoning
  • Silicosis caused by long-term exposure to silica dust
  • Some medications like anti-seizure medications, antibiotics. Drug fever often starts suddenly after the start of a new medication and usually resolves once the drug is stopped. Immediate fever after the start may be caused by an allergic reaction to the drug or a preservative in the medication.
  • Malignant tumors also make pyrogens which cause fever by triggering the hypothalamus. Some medications used in the treatment of cancer also cause fever. Further, cancer patients have a weakened immune system that increases the risk of infections and thus fever.
  • Some immunizations like DTaP or pneumococcal vaccine
  • Alcohol withdrawal and heavy alcohol use also cause fever
  • Amphetamine abuse
  • Hormone disorders like hyperthyroidism
  • Autoimmune diseases like lupus in which the immune system fails to function properly make the body prone to infections.

In some cases, the actual cause of fever cannot be identified without an extensive evaluation. Fever in which the cause is unknown is referred to as fever of unknown origin (FUO).

Fever is not contagious in most of the cases, except in viral or bacterial infection. The major risk factor for fever is the exposure to infectious agents.

People who travel extensively may get exposed to new foods, insects, and toxins that lead to traveler’s fever. Contaminated water, raw food, and unpasteurized dairy foods are some of the common causes of infection.

Insect bites may also spread infection in many countries. Working with certain animals may expose a person to some bacteria that cause fever, a condition called animal exposure fever.

3 Diagnosis and Treatment

The increase in temperature during fever is easy to measure, while the underlying cause of fever is hard to identify.

A person is said to have fever if: 

  • The temperature is over 99.9˚F in the mouth
  • The temperature in the anus is over 100˚F
  • The temperature under the arm is over 99.9˚F

Information on the onset of fever, other symptoms, immunization status of the patient, travel details, exposure to infections, medications was taken, exposure to animals, medical history, and allergies can provide important clues about the cause of the fever.

A thorough physical examination is also conducted to find the cause of the fever. In most of the cases, medical history and physical examination may help in identifying the underlying condition that causes fever. Other tests and investigations are suggested either to confirm the diagnosis or to identify the cause, if not clear.

Some common tests suggested in the diagnosis of underlying cause are: 

More investigations are suggested if the above-mentioned tests do not reveal the cause of the fever. For FUO, doctors may suggest other tests like endoscopy, PET scan, or echocardiography.

Treatment depends on the actual cause of the fever. In most of the cases, medications like acetaminophen and ibuprofen are used to reduce body temperature.

Viral infection often resolves without any specific treatment. Medications are given to control certain symptoms like fever, congestion, or a sore throat. IV fluids and medications are suggested if the infection cause vomiting and diarrhea. Antiviral medications are used in some viral infections like influenza and herpes.

Bacterial infections that cause fever are controlled by antibiotics. Hospitalization may be required based on the physical condition of the patient. Fungal infections are treated with antifungal medications.
Drug fever is controlled by stopping the drug that induces fever. Blood clots that cause fever are controlled using blood thinning medications.

Patients with the weak immune system may require close monitoring and hospitalization to prevent infections. Fever caused by heat exhaustion is a medical emergency and the person needs to be cooled immediately.

Follow-up is needed to ensure that the underlying condition is treated completely. If fever persists for more than three days even after the start of treatment, it is important to see the doctor.

Since most fever starts with an infection, preventing infection is the best way to prevent fever: 

  • Washing hands frequently and avoiding touching face and mouth
  • Avoiding contact with infected people
  • Avoiding sharing of cups, clothes, and utensils to prevent spread of infection
  • Avoiding substance abuse
  • Having plenty of water during strenuous exercise

Fever often resolves without any specific medication or with minimum medications. Appropriate treatment of the underlying condition helps in controlling fever. As the condition is treated, body temperature also comes back to normal.

Fever is potentially life-threatening only in certain conditions, like weakened immune system and meningitis. In elderly people pneumonia with fever is serious. Severe hyperthermia may lead to complications and hence quick diagnosis and treatment are important.

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