Fever
Fever is an elevation of body temperature above normal (37°C). It is usually the body’s response to disease.
Symptoms and Causes
The human body generally maintains a temperature of 37°C. Fever occurs when this temperature rises above 38°C as a result of an immune system response. Therefore, fever is a sign of disease, although it does not always indicate severity.
Although a temperature above 37.5°C is usually considered a low-grade fever, it may also be normal between 4:00 p.m. and 6:00 p.m., since body temperature is not constant and is typically lower early in the morning and higher in the mid-afternoon. Therefore, hyperthermia between 37.5°C and 38°C is not considered indicative of disease, although it should be monitored to assess its progression.
Fever may present in different patterns depending on its characteristics:
- Intermittent fever: occurs only during several hours of the day.
- Undulating fever: consists of periods of fever lasting several days, followed by weeks without fever before recurrence.
- Remittent fever: shows marked daily fluctuations but never returns to normal values.
- Evening fever: low-grade fever that consistently appears in the afternoon or evening over several consecutive days.
- Psychogenic fever: body temperature rises transiently in response to psychological factors.
- Prolonged fever: elevated temperature persists for more than 3 consecutive weeks.
Fever is a physiological ally in fighting disease; therefore, treatment is not recommended unless it causes significant discomfort or is associated with other symptoms. This approach supports recovery. The prognosis of fever depends on the underlying disease, as fever itself is not a pathology.
Symptoms
The main symptoms of fever include:
- Elevated body temperature.
- Drowsiness.
- Chills.
- Generalized muscle pain.
- Joint pain.
- Weakness.
- Loss of appetite.
- Occasionally, headache.
- In older adults, delirium and irritability are common.
- In children, seizures may occur and can last several minutes; although alarming, they are generally harmless.
Causes
The purpose of increased body temperature is to combat microorganisms responsible for various diseases. Therefore, fever has multiple causes, as it can result from numerous conditions. The most common include:
- Infections.
- Inflammatory diseases.
- Immune disorders.
- Blood clots.
- Cancer (tumor-related fever).
- Exposure to excessive heat.
- Certain medications: antibiotics, antihypertensives, anticonvulsants.
- Reactions to specific vaccines: MMR (measles, mumps, rubella), meningococcal B, DTP (diphtheria, tetanus, pertussis), pneumococcal, influenza, COVID-19.
The type of fever may provide clues to its underlying cause. Common associations include:
- Intermittent fever: pharyngitis, tonsillitis, influenza, pneumonia, sepsis.
- Undulating fever: brucellosis (a bacterial infection transmitted from animals to humans).
- Remittent fever: tuberculosis, malaria, typhoid fever, Zika virus, Ebola virus, dengue, bacterial endocarditis, deep abscesses, rheumatoid arthritis, vasculitis, lymphomas, leukemias.
- Evening fever: urinary tract infections, mononucleosis, HIV.
- Psychogenic fever: stress, anxiety, intense emotions.
- Prolonged fever: solid tumors, lymphomas, inflammatory bowel diseases, fungal infections, hyperthyroidism.
Risk Factors
The risk of developing a disease associated with fever increases in the following situations:
- Contact with a source of infection.
- Presence of an intravenous catheter.
- Use of a urinary catheter.
- Mechanical ventilation.
- Travel to endemic areas with high infection prevalence.
- Exposure to insects or animals that may transmit diseases.
- Weakened immune system.
- Use of illicit drugs.
Complications
High fever (≥40°C) may lead to complications, including:
- Febrile seizures: common in children aged 6 months to 5 years. They occur with rapid temperature increases; although alarming and requiring medical attention, they are generally not harmful.
- Dehydration: due to fluid loss from sweating and increased respiratory rate.
- Cardiac or pulmonary impairment in patients with pre-existing conditions, as both heart rate and respiratory rate increase.
- Mental status changes: confusion, delirium, or worsening cognitive function in patients with dementia.
- Temperatures between 41°C and 42°C may affect the central nervous system, cause muscle damage, or lead to organ failure.
- Above 42°C, fever may induce coma.
- Temperatures exceeding 43°C may result in death.
Which specialist treats fever?
In most cases, fever is managed within Family and community medicine, Pediatrics, and Infectious diseases. Other specialists may be involved depending on the underlying cause.
Diagnosis
Fever is usually diagnosed at home using a thermometer. The recommended methods for measuring temperature are:
- Oral: place the sensor under the tongue and close the mouth, using the lips to hold the thermometer in place. Average temperature is 37°C.
- Axillary: place the sensor in the armpit and press the arm against the body. Normal range is 36°C to 37°C, as it is typically lower than oral temperature.
- Rectal: commonly used in infants and young children who cannot maintain other positions. Lubricate the sensor and insert it into the anus with the child lying prone. Do not insert more than 2 cm into the anal canal. Temperature readings are higher than oral and axillary measurements, and values up to 37.5°C may be normal.
In clinical settings, the specialist may perform tests to identify common causes of fever:
- Physical examination:
- Inspection of the nose, throat, and ears.
- Palpation of the neck and axillae.
- Assessment of skin condition.
- Auscultation of the heart and lungs.
- Evaluation of general condition and vitality.
- Sample collection: throat and nasal secretions are obtained for laboratory analysis to detect infectious diseases.
- Blood tests: provide relevant information about the patient’s health status and the presence of inflammatory or infectious processes.
- Chest X-ray: provides imaging of lung condition.
In cases of prolonged fever without an apparent cause, additional tests from other specialties are requested to determine the underlying disease.
Treatment
Mild or moderate fever (up to 39°C) that does not cause discomfort or is not accompanied by other symptoms should generally not be treated, as treatment may mask clinically relevant signs or interfere with the body’s healing process. If treatment is needed, the following measures can be applied at home:
- Rest, as physical activity increases body temperature.
- Adequate fluid intake to reduce temperature and replace fluid loss from sweating.
- Maintain a cool indoor environment.
- Wear lightweight clothing.
- Sleep with minimal covering, typically a light sheet.
- Take over-the-counter medications, usually paracetamol or ibuprofen.
High fever (≥39–40°C) is a warning sign requiring medical attention. After determining the underlying cause, the specialist will prescribe appropriate treatment, such as antibiotics. If fever persists, alternating paracetamol and ibuprofen is often recommended to enhance their antipyretic effect.
In infants and children, treatment considerations differ from adults:
- Under 3 months: medical evaluation is required even in the absence of additional symptoms.
- 3 to 6 months:
- Less than 39°C: rest and fluid intake; if irritability or distress occurs, medical consultation is advised.
- Over 39°C: seek medical care or telephone consultation.
- 6 to 24 months:
- Administer medications prescribed for these cases (paracetamol or ibuprofen). Aspirin should be avoided.
- Ensure adequate hydration.
- Use lightweight clothing.
- If fever persists beyond 24 hours, consult a physician.
- Over 2 years: follow adult recommendations, as the risk of severe infectious disease decreases and the immune system is more developed. Nevertheless, consultation with a pediatrician within the first 24–48 hours is advisable.
Fever during pregnancy also requires immediate medical attention when it exceeds 38°C, as elevated temperature may cause miscarriage or fetal malformations, particularly during the first trimester.
In cases where fever indicates a serious underlying condition, the specialist will determine the most appropriate treatment.
