Fever of unknown origin in children: what to know

Fever is a sign of the immune system responding to something, not a diagnosis by itself. Causes can include an infection that is difficult to locate, inflammation, or less common conditions. The child’s age, energy, hydration, breathing, weight change, travel, animal contact, medicines, and vaccination history help guide the assessment. A routine viral illness may become clearer with time, while ongoing fever deserves review even if the child seems comfortable between episodes.

Measure temperature with the same reliable method and record the time, reading, medicines, fluid intake, urine, new symptoms, and periods of normal activity. Offer frequent fluids and light clothing; do not use cold baths or force food. Use fever medicine only as directed for the child’s age and weight, and do not alternate medicines unless a clinician advises it. Arrange a paediatric or primary-care review when fever persists, returns repeatedly, or has no clear explanation.

Seek urgent medical help if the child is struggling to breathe, unusually drowsy, difficult to wake, confused, dehydrated, having a seizure, or has a stiff neck. Urgent assessment is also needed for a purple or bruise-like rash that does not fade with pressure, severe pain, repeated vomiting, or a baby with fever. Bring the temperature record and medicine packaging to the visit.

Ask what examination findings might explain the fever, which tests are appropriate, how to monitor hydration, and when results or a follow-up review are expected. Mention any exposure to someone ill, recent travel, new medicines, pets, and changes in the child’s sleep, appetite, urine, or movement.