Fever and Infectious Syndromes by Organ System
Core concepts
Fever syndromes are approached by age and focus. Infants younger than 3 months with fever of 38.0 degrees C or higher need a full sepsis evaluation and empiric antibiotics. Older children: look for urinary tract infection, pneumonia, meningitis, osteomyelitis, septic arthritis, otitis media, sinusitis, pharyngitis, and lymphadenitis. Kawasaki disease is a clinical diagnosis (fever for 5 days or more plus mucocutaneous criteria); incomplete Kawasaki exists and warrants echocardiography and IVIG when suspected. MIS-C follows SARS-CoV-2 and overlaps with Kawasaki disease but often has shock and elevated inflammatory markers. Periodic fever syndromes (PFAPA) are diagnoses of exclusion.
Traps
- Do not delay antibiotics for a lumbar puncture in suspected bacterial meningitis; obtain blood culture and treat first if the child is unstable.
- Joint fluid culture can be negative in septic arthritis; do not rely on culture alone.
- A normal chest examination does not exclude pneumonia.
- In Kawasaki disease, aspirin is used for inflammation but not for varicella or influenza because of Reye syndrome.
Worked example
A 2-month-old with a temperature of 38.2 degrees C and no source: obtain blood, urine, and CSF cultures, start ampicillin plus gentamicin (add cefotaxime for meningitis), and admit. Age, not appearance alone, drives the threshold for sepsis evaluation.
Rule of thumb: age sets the risk floor, the focus sets the workup, and instability sets the speed.