Pyrexia (Fever): Causes, Symptoms, and Treatment

What is Pyrexia (Fever)?

Pyrexia, commonly known as fever, is a temporary increase in body temperature, often due to an illness. Having a fever is a sign that something out of the ordinary is happening in your body. For an adult, a fever may be uncomfortable, but it usually isn’t dangerous unless it reaches 103°F (39.4°C) or higher. For infants and toddlers, a slightly elevated temperature may indicate a serious infection.

Normal body temperature varies by person, time of day, and even how it is measured. On average, normal body temperature is considered to be around 98.6°F (37°C), but it can range between 97°F (36.1°C) and 99°F (37.2°C). A fever is generally defined as a temperature of 100.4°F (38°C) or higher.

Source: Mayo Clinic

Common Causes

A fever can be caused by a number of factors, including infections, medications, environmental factors, and certain diseases. Here are some of the most common causes:

• Infections: Most fevers are caused by infections, such as:
  • Viral infections (e.g., colds, flu, COVID-19)
  • Bacterial infections (e.g., urinary tract infections, pneumonia, ear infections)
  • Fungal infections
  • Parasitic infections (e.g., malaria)
• Heat exhaustion or heatstroke: Prolonged exposure to high temperatures can lead to fever.
• Inflammatory conditions: Diseases like rheumatoid arthritis or inflammatory bowel disease can cause fever.
• Medications: Some drugs, such as antibiotics, antihistamines, and seizure medications, may cause fever as a side effect.
• Immunizations: Vaccines can sometimes cause a low-grade fever as the body builds immunity.
• Cancer: Certain cancers, such as leukemia and lymphoma, may cause fever, especially if the cancer or its treatment affects the immune system.
• Autoimmune diseases: Conditions like lupus can result in recurrent fevers.
• Blood clots: Conditions like deep vein thrombosis (DVT) or pulmonary embolism can cause fever.
• Hormonal disorders: Hyperthyroidism can sometimes lead to an elevated body temperature.
• Teething in infants: While not a major cause of high fever, teething can sometimes lead to a slight increase in temperature.

Source: Centers for Disease Control and Prevention (CDC)

Associated Symptoms

Fever is often accompanied by other symptoms, which can vary depending on the underlying cause. Common symptoms that may occur with fever include:

• Sweating
• Chills and shivering
• Headache
• Muscle aches
• Loss of appetite
• Irritability or lethargy
• Dehydration
• General weakness
• Flushed skin
• Increased heart rate

In children, fever may also cause:

• Fussiness or excessive crying
• Difficulty sleeping
• Poor feeding or reduced fluid intake
• Febrile seizures (in some cases, especially with rapid temperature spikes)

Source: National Health Service (NHS)

When to See a Doctor

While most fevers are not serious and can be managed at home, there are times when you should seek medical attention. Contact your healthcare provider if:

• An infant younger than 3 months has a rectal temperature of 100.4°F (38°C) or higher.
• A child between 3 months and 3 years has a fever of 102°F (38.9°C) or higher.
• An adult has a fever of 103°F (39.4°C) or higher.
• The fever lasts longer than 48 hours in adults or children.
• The fever is accompanied by severe symptoms such as:
  • Severe headache
  • Stiff neck
  • Severe throat swelling
  • Rash
  • Confusion or irritability
  • Persistent vomiting or diarrhea
  • Difficulty breathing
  • Chest or abdominal pain
• There are signs of dehydration, such as reduced urination, dry mouth, or dizziness.
• The person has a weakened immune system (e.g., due to chemotherapy, HIV/AIDS, or long-term steroid use).
• The fever does not improve with treatment or worsens over time.

Source: Cleveland Clinic

Diagnosis

To diagnose the cause of a fever, a healthcare provider will typically start with a thorough medical history and physical examination. They may ask about:

• Recent illnesses or exposures
• Travel history
• Medications being taken
• Duration and pattern of the fever
• Associated symptoms

Depending on the findings, the doctor may recommend further tests, such as:

• Blood tests: To check for infections, inflammation, or other abnormalities.
• Urinalysis: To detect urinary tract infections.
• Chest X-ray: To look for pneumonia or other lung infections.
• Throat swab: To test for strep throat or other bacterial infections.
• Imaging tests: Such as CT scans or MRIs, if an abscess or other internal issue is suspected.
• Lumbar puncture (spinal tap): In cases of suspected meningitis or encephalitis.

Source: National Institutes of Health (NIH)

Treatment Options

The treatment for fever depends on its cause and severity. In many cases, fever can be managed at home with rest and fluids. However, if the fever is caused by a bacterial infection, antibiotics may be necessary. Here are some common treatment options:

Medical Treatments

• Over-the-counter (OTC) medications:
  • Acetaminophen (Tylenol) can help reduce fever and relieve discomfort.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin) or naproxen (Aleve) can also be effective.
  • Note: Aspirin should not be given to children or teenagers due to the risk of Reye's syndrome.
• Prescription medications: If the fever is caused by a bacterial infection, your doctor may prescribe antibiotics. Antiviral medications may be used for certain viral infections like influenza.
• Intravenous (IV) fluids: In cases of severe dehydration, IV fluids may be necessary.

Home Remedies

• Stay hydrated: Drink plenty of fluids like water, herbal teas, or broth to prevent dehydration.
• Rest: Adequate rest helps your body fight off infections.
• Cool compresses: Applying a damp, cool washcloth to your forehead or taking a lukewarm bath can help reduce fever.
• Lightweight clothing: Dress in light layers to avoid overheating.
• Stay in a cool environment: Keep the room temperature comfortable and use fans if necessary.

Source: World Health Organization (WHO)

Prevention Tips

While not all fevers can be prevented, you can reduce your risk by taking steps to avoid infections and other triggers:

• Practice good hygiene: Wash your hands frequently with soap and water, especially before eating and after using the restroom.
• Get vaccinated: Stay up to date on recommended vaccines, such as the flu shot, COVID-19 vaccine, and others.
• Avoid close contact with sick individuals: This can help reduce the spread of infectious diseases.
• Cover your mouth and nose: Use a tissue or your elbow when coughing or sneezing.
• Stay hydrated: Drinking plenty of fluids supports overall health and immune function.
• Eat a balanced diet: A healthy diet rich in fruits, vegetables, and lean proteins can boost your immune system.
• Exercise regularly: Physical activity can help maintain a strong immune system.
• Avoid overheating: Dress appropriately for the weather and stay in cool environments during hot days.
• Manage chronic conditions: If you have conditions like diabetes or autoimmune diseases, work with your healthcare provider to keep them under control.

Source: Centers for Disease Control and Prevention (CDC)

Emergency Warning Signs

Seek immediate medical attention if you or someone else experiences any of the following emergency warning signs along with a fever:

• Difficulty breathing or shortness of breath
• Chest pain or pressure
• Severe headache or stiff neck (could indicate meningitis)
• Confusion, seizures, or loss of consciousness
• Severe abdominal pain
• Persistent vomiting or inability to keep fluids down
• Rash that spreads quickly or bruising (could indicate a serious infection like sepsis)
• Extreme lethargy or difficulty waking
• Blue lips or face (sign of low oxygen)
• Fever in a newborn (younger than 3 months) with any temperature of 100.4°F (38°C) or higher

These symptoms can indicate a life-threatening condition that requires immediate medical intervention. Do not wait—call emergency services or go to the nearest emergency room.

Source: Mayo Clinic