What antibiotics are used to treat bacterial gastroenteritis?

Antibiotics for Bacterial Gastroenteritis

For most cases of bacterial gastroenteritis, antibiotics are NOT routinely recommended unless specific high-risk features are present, including bloody diarrhea with fever, severe illness, immunocompromised status, or specific pathogens like Shigella. 1

When to Treat Empirically

Indications for Empiric Antibiotic Therapy

Empiric treatment is indicated ONLY in these specific situations 1:

• Infants < 3 months of age with suspected bacterial etiology 1
• Bloody diarrhea (dysentery) with fever documented in medical setting, abdominal pain, and signs of bacillary dysentery (frequent scant bloody stools, fever, cramps, tenesmus) presumptively due to Shigella 1
• Recent international travel with body temperature ≥38.5°C and/or signs of sepsis 1
• Immunocompromised patients with severe illness and bloody diarrhea 1
• Suspected enteric fever with clinical features of sepsis 1

Empiric Antibiotic Choices

For adults with bloody diarrhea meeting above criteria 1:

• First choice: Ciprofloxacin 500 mg twice daily OR Azithromycin 500 mg daily (depending on local resistance patterns and travel history) 1

For children with bloody diarrhea meeting above criteria 1:

• Infants < 3 months: Third-generation cephalosporin (ceftriaxone or cefotaxime) 1
• Older children: Azithromycin (depending on local resistance and travel history) 1

Critical caveat: Fluoroquinolone resistance in E. coli is increasing globally, so local susceptibility patterns must guide choice 1. If ciprofloxacin resistance exceeds 10-20% locally, azithromycin becomes preferred 1.

Pathogen-Specific Treatment (Once Identified)

Shigella

• First choice: Azithromycin 500 mg daily for 3 days 1, 2
• Alternatives: Ciprofloxacin (if MIC < 0.12 μg/mL), ceftriaxone, or TMP-SMX if susceptible 1
• Important: Avoid fluoroquinolones if ciprofloxacin MIC ≥0.12 μg/mL even if reported as "susceptible" 1

Campylobacter

• First choice: Azithromycin 500 mg daily 1, 3
• Alternative: Ciprofloxacin (but resistance rates approach 19% in some regions) 1, 3
• Note: Treatment most effective if started early in illness 2

Non-typhoidal Salmonella

• Usually NOT treated in uncomplicated cases 1
• Treat if: Age < 3 months, age > 50 years, immunosuppressed, prosthetic devices, valvular heart disease, severe atherosclerosis, malignancy, or uremia 1
• Treatment options: Ciprofloxacin 500 mg twice daily, ceftriaxone, TMP-SMX, or amoxicillin (if susceptible) 1
• Duration: 14 days for gastroenteritis in high-risk patients 1

Salmonella Typhi/Paratyphi (Enteric Fever)

• First choice: Ceftriaxone 2g daily OR Ciprofloxacin 500 mg twice daily 1
• Alternatives: Ampicillin, TMP-SMX, or azithromycin 1
• Critical: Obtain blood, stool, and urine cultures before starting treatment 1

Vibrio cholerae

• First choice: Azithromycin (single 1g dose or 500 mg daily for 3 days) 1
• Alternative: Doxycycline 300 mg single dose 1
• Avoid: TMP-SMX (less effective than doxycycline) 1

Yersinia enterocolitica

• First choice: Fluoroquinolone (ciprofloxacin 500 mg twice daily or levofloxacin 500 mg daily) 1
• Alternative: TMP-SMX or doxycycline 100 mg twice daily 1

STEC/Shiga Toxin-Producing E. coli

• AVOID antibiotics for STEC O157 and other STEC producing Shiga toxin 2 (increases risk of hemolytic uremic syndrome) 1
• Treatment for non-Shiga toxin 2 producing STEC is controversial with insufficient evidence 1

Special Populations

Pregnant Women

• Avoid fluoroquinolones 1, 4
• Options: Ampicillin, cefotaxime, ceftriaxone, or TMP-SMZ (though TMP-SMX has theoretical folate concerns in first trimester) 1

HIV-Infected Patients

• Salmonella gastroenteritis: Consider treatment with ciprofloxacin 750 mg twice daily for 14 days to prevent extraintestinal spread 1
• Traveler's diarrhea prophylaxis: Ciprofloxacin 500 mg daily may be considered depending on immunosuppression level and travel destination 1

Pediatric Considerations

• Avoid fluoroquinolones in children < 18 years (arthropathy risk) unless no alternatives exist 1, 4
• Preferred agents: Third-generation cephalosporins, azithromycin, TMP-SMX, or ampicillin 1

Common Pitfalls

• Do NOT treat watery diarrhea empirically in immunocompetent patients—most cases are self-limited and antibiotics may prolong shedding 1
• Do NOT use antibiotics for STEC O157 or Shiga toxin 2-producing strains—this increases HUS risk 1
• Check local resistance patterns before using fluoroquinolones—resistance in E. coli and Campylobacter is widespread 1, 3
• Modify therapy once pathogen is identified and susceptibilities are available 1
• Asymptomatic contacts should NOT be treated empirically 1