Fever is one of the most common medical signs. It is characterized by an increase in internal body temperature to levels above normal. Fevers are an important part of the body’s defense mechanism against infection. However, sometimes fevers can become dangerously high. Knowing the different types of fevers and their causes can help determine when medical treatment may be needed.
1. Hyperpyrexia
Hyperpyrexia is the most severe type of fever. It is defined as a core body temperature above 107.6°F (42°C). Temperatures this high can lead to febrile seizures, brain damage, organ failure and even death if not treated immediately. Hyperpyrexia is considered a medical emergency.
Causes of hyperpyrexia can include:
- Heat stroke – Exposure to very high environmental temperatures can overwhelm the body’s temperature regulation
- Neuroleptic malignant syndrome – A rare reaction to some psychiatric medications
- Serotonin syndrome – Caused by simultaneous use of certain antidepressants
- Malignant hyperthermia – An inherited condition triggered by certain anesthesia gases
- Thyrotoxicosis – Overactive thyroid hormone production
- Drug overdose – Recreational drugs like ecstasy can raise body temperature
- Severe infections – Bacterial and viral illnesses like sepsis can drive up fever
Treatment involves aggressively lowering the person’s temperature through methods like ice water immersion, evaporative cooling and antipyretic medications. Identifying and treating the underlying cause is also important.
2. High Fever
High fevers are generally defined as core body temperatures from 103-106°F (39.4-41.1°C). They are not immediately life-threatening like hyperpyrexia but can still be a sign of serious illness.
Causes of high fever include:
- Bacterial infections – Pneumonia, meningitis, urinary tract infections
- Viral infections – Influenza, COVID-19, mononucleosis
- Immune disorders – Lupus, rheumatoid arthritis, Crohn’s disease
- Inflammatory conditions – Appendicitis, abscess, pancreatitis
- Cancers – Leukemia and lymphoma most commonly
In children, high fevers may also be associated with benign viral illnesses. However, a fever above 104°F (40°C) warrants medical evaluation even in children.
Treatment focuses on relieving discomfort and reducing the fever with acetaminophen or ibuprofen. Treating the underlying illness is also important.
3. Low Grade Fever
Low grade fevers are generally defined as 100.4-102.9°F (38-39.3°C). They are relatively common and often not a major concern, especially if the person is otherwise feeling well.
Causes of low grade fever include:
- Viral infections – Common cold, flu, COVID-19, roseola
- Bacterial infections – Ear infections, sinusitis, urinary tract infections
- Inflammation – Arthritis, autoimmune conditions
- Vaccinations – Normal immune response
- Sunburn or overheating – Heat exposure
- Medication side effects – Antibiotics, anticonvulsants
Low grade fevers usually don’t require specific treatment beyond rest and hydration. Over-the-counter fever reducers can provide comfort but are often not necessary. However, fevers over 102°F or lasting more than 3 days warrant medical evaluation.
4. Postoperative Fever
Postoperative fevers are fevers occurring after a surgical procedure. They affect up to half of patients after major surgeries.
Causes include:
- Respiratory infections
- Urinary tract infections
- Wound infections
- Atelectasis – Collapsed lung segments
- Deep vein thrombosis – Blood clots
- Medication reactions
- Inflammation from tissue trauma
Mild postoperative fevers under 101°F usually resolve within a few days and can be managed with acetaminophen. Higher fevers require investigation for infections or complications. Antibiotics may be warranted.
5. Recurrent Fevers
Recurrent fevers are characterized by episodes of fever separated by normal temperature that recur over an extended time. Some common causes include:
- Cyclic neutropenia – Cyclical decreases in neutrophils causing fevers every 21 days
- Familial Mediterranean fever – Hereditary condition causing periodic fevers and inflammation
- Autoimmune disorders – Lupus, adult Still’s disease
- Chronic infections – Abscesses, endocarditis, malaria, TB
Diagnosis involves identifying patterns between fever episodes and looking for underlying causes. Treatments target the specific illness if found. Recurrent fevers themselves can be managed with NSAIDs, steroids or newer biologic medications.
Key Points About Fever Types
- Hyperpyrexia is the most severe type of fever with body temperatures above 107.6°F (42°C). It requires emergency treatment.
- High fevers from 103-106°F (39.4-41.1°C) often indicate serious bacterial or viral illness.
- Low grade fevers from 100.4-102.9°F (38-39.4°C) are relatively common and usually not serious.
- Postoperative fevers are common after major surgery and need evaluation for complications.
- Recurrent fevers recurring periodically suggest an underlying medical condition.
Conclusion
Fevers have a wide range of causes ranging from benign to life-threatening. Mild low grade fevers are usually no cause for alarm, especially if the person is otherwise healthy. High fevers and hyperpyrexia require prompt medical evaluation and treatment. Recurrent fever patterns can provide clues to diagnosis of an underlying illness. Knowing the type of fever and associated symptoms can help determine the best course of action.