Common Viruses Causing Prolonged Fever (>5 Days) in Children Under 5
When a child under 5 presents with fever lasting more than 5 days, the primary concern should shift from common viral infections to Kawasaki Disease, as this is the most critical diagnosis to identify given its potential for permanent cardiac complications if treatment is delayed. 1, 2
Critical Diagnostic Consideration: Kawasaki Disease
Kawasaki Disease must be at the top of your differential for any child with fever ≥5 days, as this inflammatory condition—not a typical viral infection—carries significant morbidity risk. 1, 2
Fever for ≥5 days is the hallmark feature of Kawasaki Disease, with diagnosis requiring 4 of 5 additional criteria: bilateral conjunctival injection, oral mucosal changes, polymorphous rash, extremity changes, or cervical lymphadenopathy ≥1.5 cm. 1, 2
Incomplete Kawasaki Disease is most common in infants under 1 year, who paradoxically have the highest rate of coronary artery aneurysms if untreated, and may present with prolonged fever as the sole or primary finding. 1, 2
Treatment must be initiated within 10 days of fever onset to reduce coronary artery aneurysm risk from 15-25% down to approximately 5%, with IVIG (2 g/kg) and high-dose aspirin. 1, 2
Obtain ESR and CRP levels, which are typically markedly elevated (ESR often >100 mm/hr, CRP ≥3 mg/dL) to a degree not seen in common viral infections. 1
Urgent echocardiography is required for any child with suspected Kawasaki Disease. 1, 2
Common Viral Infections (Typically <5 Days Duration)
While the question asks about viruses causing prolonged fever, most viral infections in children under 5 cause fever lasting less than 1 week by definition of "fever without source." 1
The majority of febrile children have benign, self-limited viral infections that resolve within days. 1, 3
Herpes simplex virus is the notable exception among viral infections, as it can cause devastating consequences in young infants and requires specific consideration. 1, 2
The presence of one viral infection does not preclude coexisting bacterial infection, which is why prolonged fever warrants thorough evaluation. 1, 2
Age-Specific Risk Stratification for Prolonged Fever
Neonates (0-28 days) with any fever ≥38.0°C require comprehensive evaluation including lumbar puncture for CSF analysis, as they have a 13% incidence of serious bacterial infection. 2, 4
Young infants (29-90 days) have a 9% incidence of serious bacterial infection and may be risk-stratified using validated criteria. 2
Children 2 months to 2 years with prolonged fever require:
- Urinalysis and urine culture (catheterized specimen, NOT bag specimen), as UTI is now the most common serious bacterial infection (5-7% prevalence, up to 20% in uncircumcised male infants). 1, 2, 4
- Complete blood count with differential, blood culture, inflammatory markers (CRP, ESR, procalcitonin), and comprehensive metabolic panel including liver function tests. 2, 4
Other Causes of Prolonged Fever to Consider
Multisystem Inflammatory Syndrome in Children (MIS-C) occurs 2-6 weeks post-SARS-CoV-2 exposure, with children presenting with significantly higher temperatures and longer fever duration than routine pediatric illnesses. 2
Urinary tract infections account for 17.9% of serious bacterial infections in the post-vaccine era, with E. coli causing 87.4% of cases. 1
Bacterial meningitis now has an incidence of 0.9% in febrile infants, with E. coli causing 43.7% of cases in the post-pneumococcal vaccine era. 1
Common Pitfalls to Avoid
- Do not assume normal WBC count rules out bacterial infection, especially in neonates. 4
- Do not obtain bag urine specimens, as they are unreliable for UTI diagnosis. 4
- Do not administer antibiotics before obtaining cultures, as this may obscure diagnosis. 4
- Do not dismiss prolonged fever as "just a virus" without considering Kawasaki Disease, especially in children under 1 year who may have incomplete presentations. 1, 2