When do you start antibiotics in bacterial diarrhea?

When to Start Antibiotics in Bacterial Diarrhea

In most cases of acute diarrhea, antibiotics should NOT be started empirically—the key exceptions are infants under 3 months with suspected bacterial infection, patients with bacillary dysentery (Shigella), recent international travelers with high fever (≥38.5°C) or sepsis, and immunocompromised patients with severe bloody diarrhea. 1

General Principle: Antibiotics Are Usually NOT Indicated

For immunocompetent children and adults with bloody or watery diarrhea, empiric antimicrobial therapy while awaiting diagnostic results is not recommended 1. Most infectious diarrhea is self-limiting and resolves within 5 days without antibiotics 2, 3. The overuse of antibiotics contributes to antimicrobial resistance and can cause harm in certain infections 1, 3.

Specific Situations Where Antibiotics ARE Indicated

1. Infants Under 3 Months

• Start empiric antibiotics if bacterial etiology is suspected 1, 4
• Use a third-generation cephalosporin 1, 4

2. Bacillary Dysentery (Presumed Shigella)

• Treat if patient has documented fever in a medical setting, abdominal pain, bloody diarrhea, and classic dysentery symptoms (frequent scant bloody stools, fever, abdominal cramps, tenesmus) 1, 4
• First-line: Azithromycin or fluoroquinolone (ciprofloxacin), depending on local resistance patterns 1, 4
• Azithromycin is increasingly preferred due to rising fluoroquinolone resistance 4, 2

3. Recent International Travelers

• Start antibiotics if temperature ≥38.5°C and/or signs of sepsis 1, 4
• Azithromycin is preferred first-line for dysentery or febrile diarrhea, particularly from Southeast Asia and India where fluoroquinolone-resistant Campylobacter is prevalent 4
• Dosing options:
  • Azithromycin: 1000 mg single dose for dysentery, or 500 mg single dose for watery diarrhea 4, 2
  • Ciprofloxacin: 750 mg single dose or 500 mg twice daily for 3 days 4, 2

4. Immunocompromised Patients

• Empiric antibacterial treatment should be considered in those with severe illness and bloody diarrhea 1, 4
• Use fluoroquinolone or azithromycin based on local susceptibility 1

5. Suspected Enteric Fever (Typhoid)

• Patients with clinical features of sepsis should be treated empirically with broad-spectrum antimicrobials after collecting blood, stool, and urine cultures 1, 4
• Narrow therapy once susceptibility results are available 1, 4

6. Children with Neurologic Involvement

• Use third-generation cephalosporin 1, 4
• Otherwise, azithromycin based on local patterns 1, 4

Critical Contraindications: When to AVOID Antibiotics

STEC/Shiga Toxin-Producing E. coli

• Antimicrobial therapy should be avoided for STEC O157 and other STEC producing Shiga toxin 2 (or unknown toxin genotype) 1, 4
• Antibiotics may increase risk of hemolytic uremic syndrome 4
• This is a strong recommendation despite moderate evidence 1

Asymptomatic Contacts

• Do NOT offer empiric treatment to asymptomatic contacts of people with bloody or watery diarrhea 1, 4
• Advise appropriate infection prevention measures instead 1

Non-typhoidal Salmonella

• Antibiotics are not routinely recommended 4
• Only treat in severe infection, patients <6 months or >50 years, or those with prosthetics, valvular heart disease, severe atherosclerosis, malignancy, or uremia 4

Antibiotic Selection Algorithm

For Adults:

• First-line: Azithromycin (preferred in most settings due to resistance patterns) or fluoroquinolone (ciprofloxacin) 1, 4
• Consider local susceptibility patterns and travel history 1, 4
• Geographic resistance matters: fluoroquinolone resistance exceeds 90% in some regions like Thailand 4

For Children:

• Infants <3 months or neurologic involvement: Third-generation cephalosporin 1, 4
• Other children: Azithromycin based on local patterns 1, 4

Management Principles Beyond Antibiotics

Rehydration is Cornerstone

• Reduced osmolarity oral rehydration solution (ORS) is first-line for mild to moderate dehydration 1, 4, 5
• Intravenous isotonic fluids (lactated Ringer's or normal saline) for severe dehydration, shock, altered mental status, or ileus 1, 5

Modify Treatment Based on Culture Results

• Discontinue or modify antibiotics when a specific pathogen is identified 1, 4, 5
• This prevents unnecessary antibiotic exposure 5

Reassess Non-Responders

• Consider non-infectious conditions (lactose intolerance, IBD, IBS) in patients with symptoms lasting ≥14 days 1, 5
• Reassess fluid/electrolyte balance, nutritional status, and antibiotic dose/duration in persistent cases 1, 5

Common Pitfalls to Avoid

• Do not use antibiotics routinely in uncomplicated diarrhea—this drives resistance 4, 3
• Never neglect rehydration while focusing on antibiotics 4, 5
• Recognize STEC early to avoid antibiotics that increase HUS risk 1, 4
• Account for geographic resistance patterns—fluoroquinolones are increasingly ineffective against Campylobacter in many regions 4, 2
• Avoid rifaximin if invasive pathogens (Campylobacter, Salmonella, Shigella) are suspected 4, 2