Fever is one of the most common problems in pediatrics. Differentiating between bacterial infections, that require antibiotic therapy, and viral infections that resolve on their own is an important challenge for physicians.

C-reactive protein (CRP) is a protein that increases in response to inflammation and its level is generally higher in bacterial infections compared to viral infections. it can be measured by a simple blood test, however its utility as a sole marker for bacterial infection is limited.

The hypothesis of the study is that measuring CRP velocity, e.g the value of CRP divided by the hours since the fever started will improve the utility of CRP for the diagnosis of bacterial infections in children.

Inclusion Criteria:

• children less than 5 years of age,
• children with no comorbidities and fever > 38 for at least 24 hours, and
• children with no previous antibiotic therapy.

Exclusion Criteria:

• HIV,
• immunosuppressive conditions,
• antibiotic therapy.

children < 5 years of age presenting to the Emergency Department with fever