Treatment of Infectious Bacterial Diarrhea
Begin immediate oral rehydration with reduced-osmolarity ORS (65–70 mEq/L sodium, 75–90 mmol/L glucose) for all patients with bacterial diarrhea, regardless of severity—this is the cornerstone of therapy and prevents morbidity and mortality far more effectively than any antibiotic. 1, 2
Rehydration: The First and Most Critical Step
Fluid replacement supersedes all other interventions, including antibiotics, because dehydration—not the diarrhea itself—drives morbidity and mortality in bacterial diarrheal illness. 1, 2
Oral Rehydration Protocol by Severity
Mild dehydration (3–5% fluid deficit, slight thirst, mildly dry mucous membranes): Administer 50 mL/kg of ORS over 2–4 hours. 1
Moderate dehydration (6–9% deficit, loss of skin turgor, skin tenting on pinch, dry mucous membranes): Administer 100 mL/kg of ORS over 2–4 hours. 1
Severe dehydration (≥10% deficit, altered mental status, prolonged skin tenting >2 seconds, cool extremities, decreased capillary refill, rapid deep breathing): Switch immediately to isotonic IV fluids (lactated Ringer's or normal saline) until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit replacement. 1, 2
Prescribe total fluid intake of 2,200–4,000 mL/day, with the rate exceeding ongoing losses (urine output + 30–50 mL/hour insensible losses + stool losses). 1
Continue ORS until clinical dehydration resolves and diarrhea stops. 1, 2
When to Use Antibiotics: A Restrictive Approach
Do not prescribe empiric antibiotics for uncomplicated acute watery diarrhea in stable, immunocompetent adults without recent international travel—this is a strong recommendation from the IDSA. 1, 2
Specific Indications for Antibiotic Therapy
Antibiotics are reserved for these specific scenarios only:
Fever (≥38.5°C) with bloody diarrhea (suggesting invasive pathogens like Shigella or Campylobacter). 1, 2
Recent international travel with severe symptoms (fever, signs of sepsis, or moderate-severe illness). 1, 2
Immunocompromised patients with bloody diarrhea or severe illness. 2
Ill-appearing infants <3 months with suspected bacterial etiology. 2
Suspected enteric fever with sepsis features (requires immediate broad-spectrum IV antibiotics after obtaining blood, stool, and urine cultures). 2
Antibiotic Selection When Indicated
Azithromycin 500 mg single dose for watery diarrhea; 1,000 mg for dysentery is the preferred agent. 1
Ciprofloxacin 750 mg single dose or levofloxacin 500 mg single dose are alternatives based on local resistance patterns. 1, 3
Ciprofloxacin is FDA-approved for infectious diarrhea caused by enterotoxigenic E. coli, Campylobacter jejuni, Shigella species, and Salmonella typhi. 3
Rifaximin 200 mg three times daily for 3 days is FDA-approved for travelers' diarrhea caused by noninvasive E. coli in patients ≥12 years. 4
Modify or discontinue antibiotics when a specific pathogen is identified. 2
Critical Contraindication: STEC Infections
Never use antibiotics in patients with STEC O157 or other Shiga toxin 2-producing E. coli infections—antibiotics increase the risk of hemolytic uremic syndrome (HUS) by up to 50% through bacteriophage induction and increased Shiga toxin release. 5
Monitor patients with confirmed STEC and severe bloody diarrhea closely for HUS development (thrombocytopenia, elevated creatinine/BUN, hemolysis, decreased urine output). 5
Aggressive IV fluid resuscitation with isotonic crystalloids is the mainstay of STEC management to maintain renal perfusion. 5
Symptomatic Management with Loperamide
Loperamide may be used after adequate rehydration in immunocompetent adults with watery diarrhea, but it is absolutely contraindicated in children <18 years and in any patient with fever or bloody stools. 1, 2
Start with 4 mg initially, then 2 mg every 2–4 hours or after each unformed stool (maximum 16 mg daily). 1
Loperamide in inflammatory or febrile diarrhea risks toxic megacolon. 1, 2
Dietary Management
Resume a normal, age-appropriate diet immediately or as soon as rehydration is complete—do not withhold food during diarrheal episodes. 1, 2
Continue human milk feeding in infants throughout the illness. 2
Small, light meals are preferable initially, avoiding fatty, heavy, spicy foods and caffeine. 1
Adjunctive Therapies
Probiotics may be offered to reduce symptom severity and duration in immunocompetent patients (weak recommendation, moderate evidence). 1, 2
Antiemetic agents (e.g., ondansetron) may be given to children >4 years and adults after adequate rehydration to facilitate oral intake when vomiting is present. 1, 2
Oral zinc supplementation reduces diarrhea duration in children 6 months to 5 years in countries with high zinc deficiency prevalence or in malnourished children. 2
Common Pitfalls to Avoid
Never prioritize antimotility agents or antibiotics over rehydration—dehydration, not diarrhea, drives morbidity and mortality. 1, 2
Never use loperamide when fever or bloody stools are present. 1, 2, 5
Never use antibiotics routinely in acute watery diarrhea—they do not shorten illness duration in uncomplicated cases and promote antimicrobial resistance. 1, 2
Never use rifaximin if diarrhea is complicated by fever or blood in stool, or if Campylobacter jejuni, Shigella, or Salmonella are suspected. 4
Discontinue rifaximin if diarrhea worsens or persists beyond 24–48 hours and consider alternative therapy. 4
Be vigilant for Clostridioides difficile-associated diarrhea (CDAD) following any antibiotic use—CDAD can occur up to 2 months after antibacterial therapy and requires discontinuation of non-C. difficile-directed antibiotics. 4
Special Populations
Asymptomatic carriers generally do not need treatment except Salmonella Typhi carriers, who may be treated to reduce transmission. 2
Persistent diarrhea beyond 5–6 days requires consideration of non-infectious causes including inflammatory bowel disease and irritable bowel syndrome. 2, 6
In patients with severe hepatic impairment (Child-Pugh Class C), exercise caution with rifaximin due to increased systemic exposure. 4