Are You Sick?

Fever

Causes of Fever

Infection

  • Most fevers are caused by a new infection. Viruses cause 10 times more infections than bacteria. The number of germs that cause an infection are in the hundreds. Only a few common ones will be listed below.
  • Viral Infections. Colds, flu and other viral infections are the most common cause. Fever may be the only symptom for the first 24 hours. The start of other viral symptoms (runny nose, cough, loose stools) is often delayed. Viral infections can range from mild (goes away on its own after a day or two) to serious and sometimes life threatening. Antibiotics are not helpful for viral infections. They will not kill viruses.
  • Bacterial Infections.
    • Common bacterial infections include:
      • bladder and kidney infection
      • ear, sinus and throat infections
      • some chest infections (pneumonia)
      • some gastrointestinal infections
      • wound and other skin infections and
      • some types of meningitis.
    • Bacterial infections can occur on their own or can follow a viral infection. If a fever has not gone away within 3 days, it could be that there is a bacterial infection. Your doctor may want to run some tests before ordering antibiotics, such as a urine test or throat swab. Like viral infections, bacterial infections can be mild or can also be serious and life threatening. Seek care if you are feeling worse or not getting better within 72 hours.
  • Travel to high-risk areas. If you have travelled to a different region or country and developed a fever, contact a doctor. Infections from other areas can cause fever and may be serious and require specific medicines. These include malaria, tuberculosis, hepatitis A and B and Lyme disease.

Other Causes of Fever

  • Blood Clots (serious). These can occur in the legs (deep vein thrombosis) or in the lung (pulmonary embolism) and may happen along with fever. You may have swelling and/or pain in your legs, chest pain or trouble breathing along with the fever.
  • Inflammatory Problems. There are many health problems which cause inflammation in the body and a rise in temperature. Examples are rheumatoid arthritis and other joint problems.
  • Immune System Problems, such as lupus, can cause fever. If you have a weakened immune system, your body will be less able to defend itself against viral or bacterial infections. Contact your doctor if you get a fever. Examples of a weakened immune system include diabetes, sickle cell disease, HIV, cancer, organ transplant, taking oral steroids, kidney problems.
  • Heat Exhaustion. Long exposure to high temps indoors or outdoors can cause a rise in body temperature. It is worse if you're doing strenuous activity and not keeping well hydrated.
  • Immunizations. Fever may follow some immunizations such as diphtheria, tetanus, pertussis or pneumococcal vaccine.
  • Medicines. Some meds, such as antibiotics and those that treat high blood pressure or seizures, can cause fever.
  • Cancer. Some types of malignant cancer can cause fever.

Normal Temperature Range

  • Rectal. A reading of 98.6° F (37° C) is just the average rectal temp. A normal low can be 96.8° F (36° C) in the morning. It can change to a high of 100.3° F (37.9° C) late in the day. This is a normal range.
  • Oral. A reading of 97.6° F (36.5° C) is just the average mouth temp. A normal low can be 95.8° F (35.5° C) in the morning. It can change to a high of 99.9° F (37.7° C) late in the day. This is a normal range.