The Common Cold Slideshow Pictures Natural Cold and Flu Remedies Slideshow Pictures Take the Cold & Flu Quiz

Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

View Full Profile

Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

View Full Profile

Fever in Adults Causes

Viral fever

Illnesses caused by viruses are among the most frequent causes of fever in adults. Symptoms can include a runny nose, sore throat, cough, hoarseness, and muscle aches. Viruses also may cause diarrhea, vomiting, or an upset stomach.

For the most part, these viral illnesses will improve simply with time. Antibiotics will not treat a virus. Symptoms can be treated using decongestants and cough medicine bought over the counter. If diarrhea or vomiting occurs, then the person needs to be encouraged to drink fluids. Gatorade or sports drinks will replace lost electrolytes. If fluids are not staying down, then the doctor should be notified. Viral illnesses can last as long as one to two weeks.

The influenza virus is a major cause of death and serious illness in the elderly. Symptoms include headaches and muscle and joint aches, as well as the other common viral symptoms, including fever. Vaccines against seasonal influenza as well as H1N1 influenza are available. Also, antiviral medications can be administered to fight the influenza virus immediately after the symptoms start. This illness usually occurs during the winter.

Bacterial fever

Bacterial illnesses causing fever can affect almost any organ system in the body. They can be treated with antibiotics.

• Central nervous system (brain and spinal cord) infections can cause fever, headache, neck stiffness, or confusion. A person may feel lethargic and irritable, and light may irritate the eyes. This could represent meningitis or a brain infection, so the person should go immediately to the doctor.



• Lower respiratory system infections include pneumonia and bronchitis can cause fever. Symptoms include coughing, difficulty breathing, thick mucus production, and sometimes chest pain.



• Upper respiratory system infections occur in the throat, ears, nose, and sinuses. A runny nose, headache, cough, or sore throat accompanied by a fever may indicate a bacterial infection, but a viral infection is the most common cause.



• Infection of the genitourinary system may cause a person to have a burning sensation when urinating, blood in the urine, the urge to urinate frequently, and back pain along with a fever. This would indicate an infection in the bladder, kidney, or urinary tract. Antibiotics would treat such an infection.



• If the reproductive system is affected, people often see a discharge from the penis or vagina and have pelvic pain along with the fever. This may represent pelvic inflammatory disease (PID), which can cause significant damage to the reproductive organs. In this case, the person and any sexual partners should see a physician.



• Gastrointestinal system (digestive system) infections are indicated by diarrhea, vomiting, stomach upset, and sometimes blood in the stool. Blood in the stool can indicate a bacterial infection or other serious illness. Abdominal pain may be caused by an infection of the appendix, gallbladder, or liver, and medical care should be accessed.



• The circulatory system (including the heart and lungs) can be invaded by bacteria. There may not be any specific symptoms with the fever. A person may feel body aches, chills, weakness, or confusion. The condition of sepsis exists when bacteria enter the bloodstream. An infection of a heart valve can occur in people who had heart surgery in the past and in people who use IV drugs. This condition requires hospitalization and immediate treatment with IV antibiotics.



• Skin, the largest organ in our body, can also be the source of a bacterial infection. Redness, swelling, warmth, pus, or pain occurs at the site of the infection. An infection may result from trauma to the skin or even a clogged pore that becomes an abscess. Sometimes the infection needs to be drained. Antibiotics are often needed. In addition, skin can react to some toxins by producing a rash; for example, the scarlatina rash that can occur after a Strep throat infection causes scarlet fever (rash is bright red and diffuse, with some skin that develops scaling and desquamation or skin peeling off).

Fungal fever

Fungal infections can affect any organ system. Often a physician can identify these infections through a physical examination. Sometimes further testing is required and in rare instances, fungal fevers may require a biopsy to diagnose the infection. An antifungal medication will usually treat the infection.

Animal exposure fever

Certain people who work with animals can be exposed to rare bacteria that can cause fevers. In addition to the fever, the person may have chills, headache, and muscle and joint aches. These bacteria can exist in livestock, in unpasteurized dairy products, and in the urine of infected animals.

Travelers' fever

Anyone who travels, especially outside the United States, may develop fever after exposure to various new foods, toxins, insects, or vaccine-preventable diseases.

The only vaccines required by law at this time are yellow fever and cholera. Childhood vaccines such as those against measles, mumps, rubella, diphtheria, tetanus, and polio should be current prior to travel. Vaccines against hepatitis A, meningitis, and typhoid can be obtained before people travel to an area where exposure to those diseases is likely. The U.S. Centers for Disease Control and Prevention (CDC) can advise you on the current vaccines recommended for travel to various countries.

When traveling, consumption of contaminated water, uncooked vegetables, or unpasteurized dairy products can cause a low-grade fever and traveler's diarrhea. Bismuth subsalicylate (Pepto-Bismol), loperamide (Imodium), and certain antibiotics can help reduce symptoms but in some people, may prolong the disease. The symptoms of abdominal cramping, nausea, vomiting, headache, and bloating should go away in three to six days. A fever higher than 101 F (38.3 C) or the presence of blood in the stool is an indication to go to a doctor immediately.

Insect bites are a common way that infections are spread in some countries. Malaria is a serious infection that can occur after a mosquito bite. The bitten person may have fevers that come and go every few days. A blood test must be done to make the diagnosis. In certain infected areas, a traveler can take medication to prevent malaria. Lyme disease is spread by the bite of a tick. This is common in areas of the U.S. where the deer tick is found. Any infection caused by an insect bite should be evaluated by a doctor.

Drug fever

A fever that occurs after starting a new medication, without another source, may be a drug fever. The fever can occur at any time after starting the drug and should go away after the drug is stopped. Some drugs that have been associated with fever include beta-lactam antibiotics, procainamide (Procanbid), isoniazid, alpha-methyldopa, quinidine (Quinaglute Dura-Tabs), and diphenylhydantoin.

• An immediate fever may be caused by an allergic response to the medication or a preservative in the medication.

Blood clot fever

Occasionally a blood clot can develop in a person's leg and cause swelling and pain in the calf. Part of this clot may break off and travel to the lungs. This may cause chest pain and trouble breathing. In either case, a person may develop a fever because of inflammation in the blood vessels. A person with any of these symptoms should go to the hospital.

Tumor fever

Cancer can cause fever in a variety of ways. Sometimes the tumor makes pyrogens, chemicals which cause a fever on their own. Some tumors may become infected. Tumors in the brain may prevent the hypothalamus (the body's thermostat) from regulating the body temperature. Many of the medications that a cancer patient takes can cause a fever. Finally, immune systems in cancer patients may be weakened, which makes them prone to various infections.

Environmental fever

Occasionally a very high body temperature can be reached when the body becomes overheated. This condition is called hyperthermia. This often occurs with strenuous exercise or when the body is exposed to hot or humid weather. Certain drugs that alter a person's behavior may prevent that person from taking shelter from the heat. People with hyperthermia may be confused, lethargic, or even comatose. They may have an extremely high temperature and may not be able to sweat. Hyperthermia is treated differently than other causes of fever; it is a medical emergency. The affected person must be cooled immediately.

Special medical conditions

Many people have medical illnesses that prevent their immune system (defense system) from working normally. This may make it easier for a fever-causing infection to invade their body. Depending on the illness, it may be difficult to find the source of the fever. A fever in a person with limited ability to fight off infection can be very dangerous. The collagen vascular diseases and autoimmune diseases (for example, systemic lupus erythematosus, rheumatoid arthritis, and polyarteritis nodosa) may be associated with fever.

Causes of a weakened immune system

• Cancer



• Cancer treatment medication



• Organ transplant medication



• Steroid therapy for a long time



• HIV



• Age older than 65



• No spleen (after surgical removal of the spleen)



• Sarcoidosis



• Lupus



• Malnutrition



• Diabetes



• Heavy alcohol or drug use

Any person with one of these illnesses or conditions and a fever should see a doctor or go to a hospital's emergency department quickly. It is important for the proper treatment to be started right away. Quick action may save the person's life.

Another medical condition that involves fever is unusual as the cause is unknown or unexplained (although the cause may be discovered at a later date). It is termed FUO (fever of unknown origin). FUOs are defined as a temperature greater than 101 F (38.3 C) on several occasions, with more than three weeks' duration of such febrile illness, and failure to reach a diagnosis despite intensive investigation, which some investigators consider to be one week of inpatient investigation. Eventually, FUOs are found to be caused by infections (30%-40%), cancers (20%-30%), collagen vascular diseases (10%-20%), and numerous miscellaneous diseases (15%-20%) such as abscess in organs, obscure parasitic infections, and occult cancers. Unfortunately, about 5%-15% of FUO cases defy diagnosis, despite expert evaluations and many tests.

Another special medical condition involves hypothalamus regulation. Neurotransmitters and hormones (for example, thyroid hormones) work through feedback mechanisms to help the hypothalamus function. If this delicate feedback balance is interrupted, the hypothalamus may malfunction in many ways, one of which is to raise core body temperature to fever levels. Thyroid storm (also termed thyrotoxicosis) is a medical emergency in which fevers reach about 105.8 F (41 C).