Causes of fever
There are several causes for fever including infectious causes, autoimmune conditions, medications, environmental conditions, and some more serious conditions like cancer.
Common infectious causes of fever include:
- Upper respiratory tract infections: Respiratory tract infections are by far the commonest causes of fever in adults. Common cold and influenza are usually the culprits, especially in winter. Patients can have other symptoms like coughing, sneezing, muscle aches, and sometimes gastrointestinal manifestations like vomiting and diarrhea. Most upper respiratory infections are viral and cause a low-grade fever. If an upper respiratory infection is associated with a high-grade fever, it is likely to be of bacterial origin or a bacterial infection superimposed on a viral one.
- Gastrointestinal infections: Bacterial and viral gastrointestinal infections are common, especially in children and infants. They are unlikely to cause a fever in adults and tend to be of a milder course. In infants, viral diarrhea can be severe and cause life-threatening dehydration. That is why rapid oral rehydration is needed in such cases. Doctors avoid using antibiotics unless there is a clear bacterial origin to diarrhea -evidenced by high fever, bloody diarrhea, or stool analysis- since antibiotics can worsen the condition is misused.
- Tuberculosis: Tuberculosis is a bacterial infection that can cause night sweating and fever. It also presents by expectoration which can be bloody, loss of weight, and weakness.
- Abscesses: An abscess anywhere in the body can trigger fever and cause severe manifestations depending on its size and location.
- Meningitis: Meningitis is one of the most serious infections. Bacterial meningitis can cause a sharp rise in body temperature and rapid deterioration of the general condition that the patient can die within a few days. Other symptoms include severe headache, neck stiffness and pain, blurred vision, and photosensitivity.
- Parasitic infestations: Parasites do not commonly trigger fever except if they migrate through the body like ascaris or infest the blood like malaria. Malaria has a special type of fever that comes in episodes every three or four days. It is also associated with profuse sweating.
- Rheumatic fever: Rheumatic fever is a reaction to a special bacterial infection of the tonsils called streptococci. It is commonly seen in children and includes other symptoms like rash, joint pain, and chest pain if the heart is involved. It is an immunological reaction to the bacteria that can develop lifelong heart conditions unless treated.
- Bacterial endocarditis: Bacterial endocarditis is the infection of the inner lining of the heart and heart valves by special bacteria. The condition is common among patients who had previous valve damage by rheumatic fever, those with prosthetic valves, and drug addicts. It can be life-threatening.
Autoimmune conditions: Autoimmune conditions cause systemic inflammation which stimulates white blood cells to secrete excessive amount of chemicals that raise body temperature. It can be used to detect flares of the condition. Common autoimmune diseases that may cause fever include rheumatoid arthritis, systemic lupus, systemic sclerosis, and dermatomyositis.
Drugs: Several drugs can cause fever due to hypersensitivity reactions towards the drug itself as in penicillin, anticonvulsants and some antigout drugs like allopurinol. Other drugs can cause fever through its action as chemotherapy, while others can cause fever by altering the body metabolism as thyroid drugs.
Prolonged exposure to the sun and heatstroke: Severe dehydration and loss of mineral-rich sweat in excess can cause a rapid rise of body temperature.