What is the appropriate initial management and antibiotic therapy for a patient with acute bacterial gastroenteritis, including indications for antibiotics, preferred agents for common pathogens, and contraindications such as Shiga toxin‑producing Escherichia coli?

Management of Bacterial Gastroenteritis

Primary Treatment: Rehydration is the Cornerstone

The primary treatment for bacterial gastroenteritis is oral rehydration therapy (ORT) with reduced osmolarity oral rehydration solution (ORS), which should be initiated immediately regardless of whether antibiotics will be used. 1

Rehydration Protocol

For mild to moderate dehydration:

• Administer ORS 50-100 mL/kg over 3-4 hours in infants and children, or 2-4 L in adolescents and adults 1
• Children <10 kg: give 60-120 mL ORS after each diarrheal stool (maximum ~500 mL/day) 1
• Children >10 kg: give 120-240 mL ORS after each diarrheal stool (maximum ~1 L/day) 1
• Adults: ad libitum ORS up to ~2 L/day 1

For severe dehydration (shock, altered mental status, ileus):

• Administer isotonic IV fluids (lactated Ringer's or normal saline) in 20 mL/kg boluses until pulse, perfusion, and mental status normalize 1
• Switch to ORS once the patient can tolerate oral intake 1

Resume age-appropriate diet immediately after rehydration is completed—there is no benefit to delaying solid food 1

Antibiotic Therapy: Reserved for Specific Indications

When Antibiotics Are NOT Recommended

Empiric antibiotics are generally NOT indicated for most cases of bacterial gastroenteritis. 1 The majority of cases are self-limited and resolve with supportive care alone.

Critical Contraindication: Shiga Toxin-Producing E. coli (STEC)

Antibiotics are absolutely contraindicated in suspected or confirmed STEC/E. coli O157 infections because they significantly increase the risk of hemolytic uremic syndrome (HUS). 1, 2 This is one of the most important pitfalls to avoid—meta-analyses of low-risk-of-bias studies demonstrate a clear association between antibiotic use and HUS development 2.

When Antibiotics ARE Indicated

Antibiotics should be considered in these specific situations: 1

1. Infants <3 months of age with suspected bacterial etiology
2. Immunocompromised patients with severe illness and bloody diarrhea
3. Patients with fever, abdominal pain, bloody diarrhea, and bacillary dysentery (suggesting Shigella)
4. Severe dehydration with sepsis or neutropenia 3

Pathogen-Specific Antibiotic Recommendations

When antibiotics are indicated, choice should be guided by local resistance patterns and travel history: 1

For adults:

• Shigella: Ciprofloxacin 500 mg PO twice daily or azithromycin 500 mg PO once daily 1, 4
• Campylobacter: Azithromycin 500 mg PO once daily (preferred over fluoroquinolones due to resistance) 1
• Non-typhoidal Salmonella: Generally avoid antibiotics unless bacteremia suspected or high-risk patient (immunocompromised, infants <3 months, adults >50 with atherosclerosis); if needed, use ciprofloxacin or TMP-SMX 1, 4
• Typhoid fever (S. typhi): Ciprofloxacin or azithromycin 4

For children:

• Third-generation cephalosporin (e.g., ceftriaxone) or azithromycin 1
• Note: Fluoroquinolones are not first-choice in pediatrics due to increased adverse events related to joints and surrounding tissues 4

For complicated cases with neutropenia or sepsis:

• Broad-spectrum coverage: piperacillin-tazobactam, imipenem-cilastatin, or cefepime/ceftazidime plus metronidazole 3
• Cover gram-negative aerobes, gram-positives, and anaerobes 3

Symptomatic Management

Antimotility Agents (Loperamide)

Loperamide is contraindicated in children <18 years of age with acute diarrhea. 1, 5 This is an FDA-mandated contraindication due to risks of respiratory depression and cardiac adverse reactions in children <2 years, and general safety concerns in all pediatric patients 5.

For immunocompetent adults with non-bloody, watery diarrhea:

• Initial dose: 4 mg PO 3, 1
• Maintenance: 2 mg after each loose stool (maximum 16 mg/day) 3, 1

Loperamide is absolutely contraindicated in: 5

• Bloody diarrhea or dysentery
• Fever suggesting invasive bacterial infection
• Suspected Salmonella, Shigella, or Campylobacter infection
• Pseudomembranous colitis (C. difficile)
• Children <2 years (FDA black box)

Antiemetics

Ondansetron may be given to children >4 years and adolescents with vomiting to facilitate oral rehydration. 1, 6 Recent evidence shows ondansetron enhances ORS compliance and decreases hospitalization rates 6.

Adjunctive Therapies

• Probiotics: May reduce symptom severity and duration in immunocompetent patients 1
• Zinc supplementation: Reduces diarrhea duration in children 6 months to 5 years in areas with high zinc deficiency or malnutrition 1

Monitoring and Red Flags

Patients require immediate medical re-evaluation if: 1

• No improvement within 48 hours
• Worsening symptoms or clinical deterioration
• Severe vomiting preventing oral intake
• Persistent fever
• Frank blood in stools
• Abdominal distension

Continue monitoring hydration status until symptoms resolve. 1 Serial CRP levels can guide treatment response in complicated cases 7.

Infection Control

Essential measures to prevent transmission: 1

• Hand hygiene after toilet use, diaper changes, before food preparation and eating
• Use gloves and gowns when caring for patients with diarrhea
• Asymptomatic contacts do not need treatment but should follow infection prevention measures

Common Pitfalls to Avoid

1. Never give antibiotics empirically without considering STEC—wait for stool culture or PCR results if STEC is in the differential 2
2. Never delay rehydration while waiting for diagnostic results 1
3. Never use loperamide in children or in adults with bloody diarrhea/fever 1, 5
4. Never treat non-typhoidal Salmonella with antibiotics unless bacteremia or high-risk features present—antibiotics may prolong carrier state 1
5. Never combine immunosuppressive therapy without addressing infection risk in complicated cases 7