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Fever and Signs of Infection

What is a fever?

A fever is an increase in body temperature. The most common cause of fever is an infection caused by germs such as bacteria or viruses. Other causes of fever may include heat exposure, cancer, autoimmune disorders, certain medicines, or immunizations.

Body temperature can vary slightly from person to person and may depend on factors such as time of day and physical activity. The method used to take a temperature can also affect the results.

Read more about how to take a temperature.

Fever guidelines

In general, a fever is considered to be a temperature of 100.4°F (38.0°C). But the guidelines can vary by:

  • Age
  • How temperature is measured
  • Your child’s medical condition
  • Your care team’s instructions

For children over 3 months of age, fever can be defined as:

  1. An oral (by mouth) temperature of 100.9°F (38.3°C) or higher
  2. An oral temperature of 100.4°F (38.0°C) or higher that persists for 1 hour
  3. An under the arm (axillary) temperature of 99.9°F (37.7°C)
  4. An under the arm temperature of 99.4°F (37.4°C) or higher that persists for 1 hour

In a child younger than 3 months, a fever is an under the arm temperature of 99.4°F (37.4°C) or higher.

Always follow your care team's guidelines for fever.

Signs of fever are chills, headache and body aches, low energy, not feeling well, skin that feels hot to the touch, and flushed cheeks

Symptoms of infection

Fever is a common sign of infection. Sometimes, it is the only sign. Other signs and symptoms of infection may include:

  • Chills
  • Sweats
  • Sores or pain in any area
  • Runny nose, congestion
  • Coughing unlike before
  • Sore throat
  • Shortness of breath
  • Stiffness in neck
  • Stomach pain
  • Vomiting
  • Pain with peeing
  • Peeing more often
  • Vaginal discharge or irritation
  • Sores or pain around the rectum
  • Diarrhea

Fever in patients with neutropenia

An infection can be life threatening in children with cancer or another illness that causes neutropenia. Neutropenia is a condition that happens when the number of infection-fighting white blood cells (neutrophils) is low.

Patients with neutropenia cannot fight infections well. They can become very ill quickly. If your child has neutropenia, it is important to watch for fever or other signs of an infection. Fever or infection in a patient with neutropenia is a medical emergency.

What to do if your child has a fever or signs of infection

Contact your health care provider or go to the Emergency Room right away if you notice fever or other signs of infection in your child.

  • If it is during the day and you are close to your child’s hospital, call your child’s care team or primary clinic.
  • If it is after hours or the weekend, follow your hospital’s procedure for after-hours emergencies. Tell your primary clinic or the doctor on call as soon as you are aware that your child has a fever.
  • If you are not close to your child’s hospital, call your child’s local care provider or go to the emergency room at your local hospital.

If you go to a doctor or hospital at home, contact your child’s primary clinic or care team to give them an update on your child’s condition as soon as you can.

Be sure to tell the care providers about your child’s medical condition and where your child is being treated. They also need to know if your child has a central venous catheter (central line) and if your child has been getting chemotherapy or other drugs that weaken the immune system.

How to prevent infection

Simple steps can help to prevent infections:

  • Wash hands often with soap and water or use hand sanitizer.
  • Avoid contact with people who are sick.
  • Practice good personal hygiene, including bathing and keeping wounds clean.
  • Stay up to date on vaccinations as recommended by your doctor.
  • Wear a face mask and practice physical distancing as recommended.
  • Perform daily oral (mouth) care as instructed by your medical team. This can help prevent sores that could lead to more severe infections.
  • Keep patient living areas clean.
  • Be aware of infection sources such as flowers, animals, and dirt.
  • Wear disposable gloves and take care to prevent germs when doing care tasks such as changing diapers, line care, dressing changes, or wound care.

Questions to ask your care team

  • How often should I check my child’s temperature?
  • When should I call the care team?
  • What symptoms should I be most concerned about?
  • What are the best ways to prevent infection?
  • When is it safe to return to normal activities after a fever?

Key points about fever and signs of infection

  • Fever is an increase in body temperature often caused by infection.
  • In children 3 months and older, fever is an oral (by mouth) temperature of 100.9°F (38.3°C) or higher, or an oral temperature of 100.4°F (38.0°C) or higher that persists for 1 hour.
  • Infection can be life-threatening in children with neutropenia, or low white blood cells.
  • Watch for signs of infection.
  • Prevent infection by washing hands and keeping areas clean.
  • If you think your child has an infection, call your care team.

Related Factsheets

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Reviewed: February 2024

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