What is the most likely cause of vomiting in an infant with a recent viral upper respiratory infection (URI)?

Common Cause of Vomiting in an Infant with Recent Viral URI

The most common cause of vomiting in an infant following a viral upper respiratory infection is viral gastroenteritis, often with rotavirus being the predominant pathogen, though the viral URI itself can directly trigger vomiting through post-nasal drainage and increased nasal mucosa responsiveness. 1, 2

Primary Mechanisms

Direct viral gastroenteritis is the leading cause, with rotavirus being the single most important pathogen causing severe, dehydrating gastroenteritis in infants and young children. 1 The characteristic presentation includes:

• Vomiting is particularly prominent in rotavirus gastroenteritis, often more so than diarrhea 1
• Fever typically accompanies the vomiting 1
• Diarrhea follows, with dehydration being a frequent complication due to combined fluid losses 1
• Virtually all children are infected with rotavirus by age 3 years 1

Post-viral nasal inflammation can also trigger vomiting through increased responsiveness of the nasal mucosa to irritants after a viral URI, as noted by the American Academy of Allergy, Asthma & Immunology. 2

Critical Complications to Exclude

While viral gastroenteritis is most common, acute otitis media (AOM) complicating the URI occurs in approximately 37% of viral URI episodes in young children and can present with vomiting. 3 The overall incidence of otitis media complications following URI reaches 61% in infants. 3

Acute bacterial sinusitis should be considered if symptoms persist beyond 10 days without improvement or worsen after initial improvement, though vomiting is not the primary presenting symptom. 2

Red Flags Requiring Urgent Evaluation

Projectile vomiting is a red flag symptom requiring thorough evaluation for serious conditions including hypertrophic pyloric stenosis (most common surgical cause in 2-8 week-old infants) or malrotation with volvulus. 4

Bilious (green) vomiting indicates obstruction distal to the ampulla of Vater and requires immediate imaging with upper GI contrast series, as this suggests malrotation with potential volvulus—a surgical emergency. 4, 5

Other concerning features include:

• Blood in vomit or stool 4
• Abdominal distension 4
• Poor weight gain or weight loss 4
• Lethargy or ill appearance 4

Practical Clinical Approach

For typical non-bilious, non-projectile vomiting after viral URI:

• Assess hydration status by evaluating capillary refill, urine output (should have ≥4 wet diapers per 24 hours), and clinical signs of dehydration 4
• Continue breastfeeding on demand if breast-fed 4
• Administer oral rehydration solution in small, frequent volumes (5 mL every minute initially) for any dehydration 4
• Replace each vomiting episode with 10 mL/kg of oral rehydration solution 4

Antiemetics are generally NOT indicated for routine viral gastroenteritis in infants, though ondansetron (0.2 mg/kg oral, maximum 4 mg) may be considered only if persistent vomiting completely prevents oral intake. 4

Common Pitfall

Parents often cannot differentiate between viral URI and allergic rhinitis in young children, particularly those attending daycare with recurrent symptoms. 2 However, the presence of fever and acute onset strongly favors viral infection over allergic causes. 2 The key distinguishing feature is that viral URI symptoms typically peak by days 3-6 and then improve, whereas persistent symptoms beyond 10 days suggest bacterial sinusitis rather than uncomplicated viral illness. 2