In milk‑fed infants aged 0–12 months, what are the most common pathogens causing acute gastroenteritis and what is the recommended first‑line management?

Common Pathogens Causing Gastroenteritis in Milk-Fed Infants

Norovirus is now the most common pathogen causing acute gastroenteritis in milk-fed infants aged 0-12 months, accounting for 27% of hospitalized cases and 58% of all gastroenteritis illnesses, followed by rotavirus at 21% in hospitalized children. 1, 2

Viral Pathogens (Most Common Overall)

Viruses account for approximately 70% of acute gastroenteritis episodes in infants, with the following distribution: 3

• Norovirus: The leading cause since rotavirus vaccine introduction, responsible for 27% of hospitalized cases and nearly 1 million ambulatory care visits annually 1, 2
• Rotavirus: Second most common at 21% in hospitalized children, though previously the dominant pathogen before vaccine introduction; 17% of rotavirus hospitalizations occur in the first 6 months of life, increasing to 40% by age 1 year 1, 2
• Enteric adenovirus (types 40 and 41): Accounts for 6% overall, but more frequent in infants under 12 months at 9.4% 4

Clinical Presentation of Viral Gastroenteritis

Viral gastroenteritis typically presents with: 5

• Acute onset of fever and vomiting (occurs in 80-90% of cases)
• Watery diarrhea beginning 24-48 hours after vomiting
• Upper respiratory tract symptoms
• Generally mild disease with 3-8 day duration
• Vomiting usually resolves within 24 hours

Bacterial Pathogens (Less Common but More Severe)

Bacterial pathogens cause more severe disease with bloody stools, abdominal pain, and systemic complications, accounting for approximately 30% of cases: 1, 5

• Salmonella enterica subspecies: 42% of bacterial cases (24% overall in some studies), with 84.9% presenting with dehydration 1, 5, 6
• Campylobacter jejuni: 28% of bacterial cases (3.4-7% overall), more common in children over 5 years 1, 5, 4
• Enterotoxigenic E. coli (ETEC): 9% of cases 5
• Enteropathogenic E. coli (EPEC): 7% of cases 5
• Shigella: 21% of bacterial cases (4% overall), with 74.3% presenting with bloody diarrhea 1, 5, 6
• Yersinia: 5% of bacterial cases, with 61.5% presenting with fever 1, 6

Clinical Presentation of Bacterial Gastroenteritis

Bacterial infections present more severely with: 5, 6

• Bloody stools (especially Shigella)
• Abdominal pain and cramps
• Higher fever rates
• Shock and convulsions in severe cases
• Milk intolerance
• More prolonged dehydration

Age-Specific Vulnerability

Infants under 6 months represent a particularly vulnerable group, with: 4

• 18.7% of rotavirus cases occurring in this age group
• 60% of cases with no identified pathogen (highest proportion of any age group)
• Higher risk of severe dehydration due to higher body surface-to-weight ratio and complete dependence on caregivers 7

Mixed Infections

Mixed infections occur in approximately 12% of patients, most commonly: 5, 6

• Campylobacter + EPEC (88.9% with vomiting, 77.8% with dehydration)
• Rotavirus + Shigella + E. coli
• Rotavirus + Giardia

First-Line Management

Oral rehydration solution (ORS) is the first-line treatment for mild to moderate dehydration, administered as 5-10 mL every 1-2 minutes via spoon or syringe, successfully rehydrating >90% of infants without antiemetic medication. 2, 7

Rehydration Protocol by Severity

• Mild dehydration (3-5% fluid deficit): 50 mL/kg ORS over 2-4 hours 7
• Moderate dehydration (6-9% fluid deficit): 100 mL/kg ORS over 2-4 hours 7
• Severe dehydration (≥10% fluid deficit): Immediate intravenous rehydration required 2, 7

Ongoing Loss Replacement

Replace ongoing losses with: 7

• 10 mL/kg ORS for each watery stool
• 2 mL/kg ORS for each vomiting episode

Nutritional Management

• Continue breastfeeding throughout the illness 7
• Resume age-appropriate diet immediately during or after rehydration 7
• Avoid foods high in simple sugars, high-fat foods, and caffeinated beverages 7

Critical Red Flags Requiring Immediate Attention

Severe dehydration constitutes a medical emergency with the following signs: 2, 7

• Severe lethargy or altered consciousness
• Prolonged skin tenting (>2 seconds)
• Cool, poorly perfused extremities with decreased capillary refill
• Rapid, deep breathing indicating metabolic acidosis
• Absent bowel sounds (absolute contraindication to oral rehydration)

Medications to Avoid

Never administer the following in infants with acute gastroenteritis: 7

• Loperamide or other antimotility agents in children <18 years (serious adverse events including ileus and deaths reported)
• Metoclopramide (counterproductive as it accelerates transit)
• Adsorbents, antisecretory drugs, or toxin binders (no demonstrated effectiveness)

When to Consider Antibiotics

Antibiotics are indicated only for specific bacterial pathogens with fever and bloody diarrhea: 1

• Salmonella (in severe cases)
• Shigella
• Campylobacter

Critical caveat: Rule out STEC (Shiga toxin-producing E. coli) before starting antibiotics, as antimicrobial therapy increases the risk of hemolytic uremic syndrome 8

Hospitalization Criteria

Admit infants with: 2, 7

• Severe dehydration (≥10% fluid deficit)
• Signs of shock
• Failure of oral rehydration therapy
• Altered mental status
• Intractable vomiting despite antiemetics
• Age <3 months (lower threshold due to higher risk)
• Immunocompromised status