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medical fever thermometer test prods universal & rectal

Image: “Medical fever thermometer test prods (universal & rectal).” by Gelegenheitsautor2015 – Own work. License: CC BY-SA 4.0

Definition of the Febrile Child

Before we discuss the different causes of fever in children and how to approach a febrile child, we need to define three important terms: fever in children, fever without an identifiable cause and fever of unknown origin.

A child is said to have developed a fever when his or her core temperature, measured rectally, is 38° C or more. While the cause of the fever can be identified in some cases, others remain without a clear etiology. Fever without an identifiable cause is defined as a fever in a child that has a duration equal to or less than one week. When the cause of the fever is not known and the fever lasts more than one week, the term fever of unknown origin is used.

Measurement of the Temperature in a Febrile Child

Fever in a child is a bodily response and not a diagnosis per se. The best way to measure the core temperature is via the rectal route. The rectal measurement may be cumbersome and time-consuming thus easier routes are considered which include:

  • Measurement using the ear thermometry, the sensitivity of this route is inferior to rectal measurement.
  • Axillary measurement.
  • Skin measurements from the forehead.

Systemic Approach to the Febrile Child

When a child presents to the emergency department or to your office complaining of a fever, it is advisable to follow a systemic approach in order to not miss any possible obscure causes of the fever.

A three-step approach was suggested in a recent study for the evaluation of children with fever. The first step is to check for a possible cause of the fever. The second step is about determining the seriousness of the condition and whether the child needs to be admitted to hospital. The final third step is about re-evaluation and ordering specific supportive tests to confirm a diagnosis or exclude one.

Step 1: Determination of the cause of fever

A physical examination and history taking are essential to determine the most likely cause of fever in the child. The duration of fever, maximum documented fever, fever variation during the day and fever persistence are the most important points to check in this step.

Possible associated symptoms such as diarrhea, rash, cough or localized pain can point towards a possible diagnosis. For example, gastroenteritis can present with fever that is associated with diarrhea. A child with upper respiratory tract infections or pneumonia can present with fever and cough. Septic arthritis is presented with fever and localized painful swelling to a single or multiple joints.

red blood cells in sickle cell disease

Image: “Photomicrograph of normal-shaped and sickle-shape red blood cells from a patient with sickle cell disease.” by Gregory Kato – Own work. License: CC BY-SA 4.0

Another important checkpoint in this step is to establish whether the child might have a severe bacterial infection. Children who are on immunosuppressive therapy, who have primary immunodeficiencies, or who have been previously diagnosed with sickle-cell anemia are at risk of having a serious infectious etiology behind their fever. Children with a malignant disease or congenital heart defects are also at risk of having a severe bacterial infection as the cause of their fever.

Finally, it is vital to perform a complete physical examination of the child to identify a possible source of the fever. Chest auscultation, cardiovascular examination and throat, and ear examinations should be carried out in any child who presents with a fever.

Organisms causing UTI, bacteremia, or meningitis

  • E. coli (vast majority)
  • Group B strep (in GBS positive undertreated mothers)
  • Strep. pneumoniae
  • Neisseria meningitidis
  • Enterococcus
  • Klebsiella
  • Staph. aureus (osteomyelitis of the newborn)

Step 2: Hospitalization versus outpatient care

Determination of the cause of the fever can provide clues about the severity of the condition and whether inpatient treatment is needed. Some clues that indicate a child needs hospital admission include:

  • The unstable child that needs multiple repeated physical examinations due to the condition’s instability.
  • Septic shock patients.
  • High-risk patients, such as immunosuppressed and chronic disease patients.
  • Choice of empiric treatment requires admission.

According to a recent meta-analysis, if the child looks ill, the physical examination is grossly abnormal, or has a previous history of a medical condition; hospitalization is preferred to outpatient treatment. Another important point in favor of hospitalization is your judgment as a physician. If you really have a feeling that something is seriously wrong with the child, this can be considered as a strong red flag and the child should be admitted.

Children, who are cyanotic, have petechiae, have high-grade fever > 40° C and are hypoxic need to be hospitalized for inpatient care. Additionally, children who have an abnormal urinalysis, leukocytosis or leukopenia, and an elevated C-reactive protein are more likely to have a severe bacterial infection and should be provided with inpatient care rather than outpatient care.

Interpreting the UA

Result on UA Sensitivity Specificity
WBC count 0.74 0.86
Bacteria present 0.88 0.92
Leuko esterase 0.79 0.87
Nitrite 0.46 0.98
Entire UA 0.97 0.70

Step 3: Re-evaluation and ordering more specific tests

The last step in this suggested approach is about the re-evaluation of the feverish child. If the fever persists despite adequate treatment, i.e. antibiotics for an infectious etiology, the child should be re-evaluated. More specific tests such as a differential blood count, C-reactive protein testing and a repeat urinalysis should be performed.

Neonates who are possibly septic should have their interleukin-6 concentration measured to assess the condition’s severity and confirm the diagnosis.

Fever of an Infectious Etiology Without an Identifiable Source

Another important entity to the discussion of fever in children is the diagnosis and management of fever in a child who is likely to have an infectious etiology, but a source of the infection is not possible to identify.

The table summarizes the most likely causative organisms of fever of an infectious etiology in children according to age and provides some comments about the treatment of choice.

Child’s Age Causative Organisms Treatment Options
Neonates Group B streptococci, Staphylococcus aureus, and Listeria monocytogenes Hospitalization

IV Ampicillin + Cefotaxime

Up to 3 months Viral: Respiratory syncytial virus, influenzae viruses.

Bacterial: Enterobacter, Salmonella, E. coli

Use step 2 to determine if hospitalization is needed

If hospitalized: IV Cefotaxime

3 months to 6 years Viral: Respiratory syncytial virus, influenzae viruses, adenoviruses.

Bacterial: Streptococcus pneumonia, haemophilus influenzae b

Use step 2 to determine if hospitalization is needed

Fever of Unknown Origin

When the cause of the fever is not identified, and the fever persists for more than one week, the term fever of unknown origin is used. More careful examination and ordering of more specific tests might shed some light on the cause of fever in this group of patients.

The causes can be classified into:


  • OsteomyelitisEpstein-Barr virus infections, and urinary tract infections are common causes of fever of unknown origin.


  • Include causes such as fever following inflammatory bowel disease and fever as a side-effect to a drug.


  • Febrile episodes are seen with tumors such as leukemia, lymphoma, or Wilms tumors and renal-cell carcinoma that can present with fever and night sweats.

Idiopathic/no cause

  • Factitious fever is a possible cause of fever in children and can be identified when the fever seems to improve while at the hospital, recur once at home, be normal when measured by a healthcare provider, and be abnormal when measured by the caretaker of the child.

Juvenile idiopathic arthritis, systemic lupus erythematosus, and other collagen disorders can also present with fever of unknown origin before the onset of more specific symptoms that point towards the diagnosis.

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