Fever without localising signs in young children

What it is

A child has a fever and the examination shows no source for it. For children with a fever without localizing signs, management depends on the child's age and findings on examination, and those two things alone move the child between three very different plans.

What the examination has to show

The worked case is what a fever without localizing signs means in practice. A 5-month-old is brought for a fever to 103.1 F over the past 2 days, her immunizations are up to date, and she does not appear ill. Her rectal temperature is 39.0 C (102.2 F), heart rate 90 beats/min, respiratory rate 40/min, and oxygen saturation 98% on room air. She is alert and responsive, appears well hydrated, and has no rash or petechiae. The HEENT examination including the fontanelles is normal, the chest is clear, there are no murmurs, and the abdomen is soft.

Every one of those is a place a source could have been and was not. It is the normal examination, not how high the fever is, that puts the child on this ladder at all.