What are the differential diagnoses for fever and vomiting in a pediatric patient?

Differential Diagnosis for Fever and Vomiting in Pediatric Patients

The differential diagnosis for fever and vomiting in pediatric patients must be approached systematically by age, with infants ≤90 days requiring immediate consideration of serious bacterial infections (bacteremia, meningitis, urinary tract infection), while older children warrant evaluation for gastroenteritis, pneumonia, appendicitis, intussusception, and less commonly, food protein-induced enterocolitis syndrome (FPIES).

Age-Stratified Approach

Infants ≤3 Months (High-Risk Group)

This age group demands urgent attention as 8-13% have bacterial infections despite well appearance 1. The most critical diagnoses to exclude are:

Life-Threatening Infections

• Bacteremia and bacterial meningitis - Infants <28 days are at highest risk 1
• Urinary tract infections - The predominant bacterial infection in this age group 1
• Pneumonia - Present in only 1-3% of febrile young infants, but must be considered 1

Key clinical point: Fever is often the only sign of serious illness in young infants, making clinical differentiation from benign viral illness extremely difficult 1. Delayed diagnosis increases morbidity and mortality 1.

Viral Gastroenteritis

• Approximately 75% of well-appearing febrile children without identified source have self-limited viral infections 1
• Characterized by diarrhea with accompanying nausea, vomiting, fever, and abdominal pain 2

Non-Infectious Causes to Consider

• Food protein-induced enterocolitis syndrome (FPIES) - Often missed because allergy is not considered in sepsis-like presentations 3
  • Presents with profuse vomiting and severely altered consciousness
  • Can mimic sepsis, requiring high clinical suspicion 3

Children 3 Months to 2 Years

Gastrointestinal Causes

• Acute gastroenteritis - Most common cause 2

• Intussusception - Critical diagnosis not to miss 4

  • Classic triad (abdominal pain, hematochezia, palpable mass) seen in only a minority
  • Presents with wide variety: vomiting, fever, lethargy, abdominal pain 4
  • Ultrasound is safe, sensitive, and specific; should be performed early with any clinical suspicion 4
  • Plain radiography lacks sensitivity to exclude intussusception 4

• Appendicitis - Consider in appropriate clinical context 1

Respiratory Causes

• Pneumonia - Evaluate per localizing respiratory symptoms 1

Urinary Tract Infection

• Remains important consideration across all pediatric ages

Older Children (>2 Years)

Recurrent/Chronic Presentations

• Syndrome of undifferentiated recurrent fever (SURF) 5

  • Distinguished from PFAPA by prominent GI symptoms: nausea, vomiting, abdominal pain
  • Inconsistent response to steroids
  • IL-1 mediated inflammation

• Fever of unknown origin (FUO) - Fever >3 weeks without identified source 1

  • Represents 1-2% of young febrile infants with invasive bacterial infection

Critical Evaluation Steps

Immediate Risk Stratification

For infants ≤60 days: Evaluation must include 6:

• Urinalysis
• Blood culture
• Inflammatory markers
• Consider lumbar puncture based on risk stratification
• Hospital admission with empiric antibiotics in most cases

Dehydration Assessment

The three most useful predictors of ≥5% dehydration are 2:

1. Abnormal capillary refill
2. Abnormal skin turgor
3. Abnormal respiratory pattern

Low serum bicarbonate combined with clinical parameters predicts dehydration, though BUN/creatinine ratio evidence is conflicting 2.

Common Pitfalls to Avoid

1. Assuming all fever/vomiting is viral gastroenteritis in young infants - 8-13% have serious bacterial infections 1

2. Relying on plain radiography to exclude intussusception - Ultrasound is required 4

3. Missing FPIES - Consider in infants with sepsis-like presentation and profuse vomiting, especially if allergy history present 3

4. Overlooking special populations:

   • Neonates and neutropenic patients are at higher risk for serious bacterial infection 1
   • Infants <28 days have highest risk 1

5. Inadequate follow-up - Even low-risk infants managed at home have 1-2% subsequent admission rate 6

Management Considerations

For gastroenteritis with dehydration: Oral rehydration therapy is equally efficacious as IV rehydration for mild-moderate dehydration 2. Ondansetron decreases vomiting, improves oral intake success, reduces IV rehydration need, and shortens ED stay with minimal side effects 2.

For young febrile infants: Even well-appearing infants with difficulty feeding, vomiting, and decreased urine output may require parenteral therapy if bacterial infection cannot be excluded 6.