Prolonged Fever in Children: When to Worry and Seek Immediate Medical Evaluation

Fever ≥100.4°F (38°C) lasting >3 days in a child warrants medical evaluation. Fever persisting >20 days is not common and suggests serious underlying pathology requiring urgent investigation.

Common Causes of Prolonged Fever

• Infectious: Occult UTI, tuberculosis, endocarditis, osteomyelitis, EBV/CMV, malaria (travel).
• Autoinflammatory/autoimmune: SJIA, PFAPA, Kawasaki disease, SLE, vasculitis.
• Malignancy: Leukemia, lymphoma, neuroblastoma.
• Drug fever: Antibiotics, anticonvulsants.
• Factitious / Munchausen by proxy.

Workup (Fever of Unknown Origin - FUO)

1. Detailed history/exam (travel, exposures, pets, medications).
2. CBC, differential, CRP, ESR, blood culture ×2–3, urinalysis/culture.
3. Chest X-ray, abdominal ultrasound.
4. Targeted serologies, ANA, ferritin, LDH, immunoglobulins.
5. Advanced imaging (CT/MRI/PET) and biopsy as directed.

Early specialist referral (pediatric ID, rheumatology, oncology) improves diagnostic yield.