From the Guidelines
Fever is defined as a body temperature greater than 38°C, according to the most recent guidelines from the Society of Critical Care Medicine and the Infectious Diseases Society of America 1.
Definition of Fever
The definition of fever can vary depending on the context and population, but generally, it is considered as a temperature above the normal range of 97-99°F (36.1-37.2°C).
- The normal body temperature range is subject to various factors such as age, gender, diurnal variation, and sampling site.
- The United States Centers for Disease Control and Prevention defines fever in the diagnosis of hospital-acquired infections as a measured temperature of greater than 38°C.
Causes and Symptoms of Fever
Fever occurs as part of the body's immune response to infection, inflammation, or other medical conditions.
- When the body detects pathogens like bacteria or viruses, the immune system releases chemicals called pyrogens that travel to the brain's hypothalamus, which acts as the body's thermostat.
- These pyrogens reset the body's temperature to a higher level, causing the body to generate and retain more heat.
- Common accompanying symptoms may include sweating, chills, headache, muscle aches, and fatigue.
Management of Fever
For adults, fevers can be managed with over-the-counter medications like acetaminophen (325-650mg every 4-6 hours, not exceeding 3000mg daily) or ibuprofen (200-400mg every 4-6 hours with food) 1.
- Staying hydrated, resting, and using light clothing and bedding can also help manage fever symptoms.
- While most fevers resolve on their own, medical attention should be sought for very high fevers (above 103°F/39.4°C), fevers lasting more than three days, or when accompanied by severe symptoms like difficulty breathing, confusion, or stiff neck.
Special Considerations
Not all patients with infection manifest fever, and the absence of fever in patients with infection is associated with worse outcomes 1.
- The recommendations for managing fever may generally apply to patients with suspected infection regardless of the presence of temperature elevation.
- It is essential to consider the individual's overall clinical presentation, medical history, and other factors when evaluating and managing fever.
From the Research
Definition of Fever
- Fever is a complex physiological response involving the innate immune system and should not be characterized merely as a temperature above the normal threshold of 37.0°C (98.6°F) 2.
- It is a cardinal symptom of most infectious diseases, but can also be caused by non-infectious conditions 3.
- Fever is part of a systemic inflammatory response by the immune system to infection, and is characterized by a regulated rise in body temperature that is defended by fully functional thermoregulatory mechanisms 4.
Characteristics of Fever
- The normal daily variation in body temperature is typically around 37.0°C (98.6°F), but fever can cause the body temperature to rise above this threshold 2.
- Fever can be measured in different ways, including rectal, tympanic, oral, or axillary temperatures, with different normal ranges for each method 5.
- The elevation in body temperature during fever is a regulated rise that is defended by fully functional thermoregulatory mechanisms, and can be treated with aspirin-like drugs 4.
Distinction from Hyperthermia
- Fever differs from other forms of hyperthermia, such as exercise hyperthermia or hyperthermias due to inadequate means of heat dissipation, in that it is a regulated rise in body temperature that is defended by fully functional thermoregulatory mechanisms 4.
- Fever is the only form of hyperthermia that can be attributed to an upward displacement of the "set point" for body temperature regulation, and is the only form that can be effectively treated with aspirin-like drugs 4.
Clinical Significance
- Fever is a common symptom of many infectious diseases, and can be a challenge for physicians to diagnose and treat 2, 3.
- The clinical approach to diagnosis and management of fever is changing, with new concepts and imaging techniques emerging 2.
- Fever research has provided new insights into temperature and energy homeostasis, and into treatment of infection and inflammation 6.