Bacterial gastroenteritis accounts for a significant proportion of the estimated 179 million outpatient visits for acute diarrheal disease annually in the United States, with approximately 5.2 million cases of bacterial diarrhea per year, leading to ~46,000 hospitalizations and ~1,500 deaths. [1-2] The most commonly identified bacterial pathogens in North America are Salmonella, Campylobacter, Shigella, and Shiga toxin–producing E. coli (STEC). [1] Most cases are self-limited, but recognizing alarm features and high-risk populations is critical for appropriate escalation.
The following algorithm from the AAFP provides a practical framework for evaluation and management:
1. History
- Onset, frequency, volume, and duration of diarrhea (≥3 loose/watery stools per day defines acute diarrhea) [1]
- Stool character: watery vs. bloody/mucoid — bloody stools suggest invasive or toxin-producing organisms (Shigella, Salmonella, Campylobacter, STEC) [1][3]
- Timing and incubation period: nausea/vomiting within 1–6 hours suggests preformed toxin (S. aureus, B. cereus); 8–16 hours suggests C. perfringens; 16–72 hours suggests invasive bacterial pathogens [3]
- Associated symptoms: fever, tenesmus, abdominal cramping, vomiting, myalgias
- Exposures: recent travel (especially to low-income countries), undercooked meat/poultry/eggs, raw shellfish, unpasteurized dairy, contaminated water, restaurant/buffet meals [3]
- Contacts: sick household members, daycare/institutional exposure, outbreak setting
- Recent antibiotics (raises concern for C. difficile), PPI use, hospitalization [4]
- Sexual history: MSM at higher risk for Shigella, enteric pathogens [3]
- Important negatives: absence of fever with bloody diarrhea raises concern for STEC [3]
2. Alarm Features
- Grossly bloody stools (dysentery) [4]
- High fever ≥38.5°C (101.3°F) — warning sign of complicated illness or bacteremia [4]
- Signs of sepsis: tachycardia, hypotension, altered mental status [1]
- Severe dehydration: decreased urine output, syncope, confusion, poor skin turgor [3]
- Severe abdominal pain or peritoneal signs (consider surgical abdomen, toxic megacolon, perforation) [4]
- Age ≥65 years — increased risk of severe disease and death [1]
- Immunocompromised state [1]
- Symptoms >7 days without improvement [1]
- Suspected STEC — risk of hemolytic uremic syndrome (HUS), especially with Shiga toxin 2 [3]
3. Medications
Relevant contributors
- PPIs increase susceptibility to enteric infections [4]
- Recent antibiotics raise concern for C. difficile [1]
- Chemotherapy/immunosuppressants increase risk of severe or invasive disease [1]
Common treatments
- Loperamide 4 mg initial dose, then 2 mg after each unformed stool (max 8 mg/day for 48 hours) — for acute watery, non-bloody, non-febrile diarrhea only [4]
- Bismuth subsalicylate — safe alternative in inflammatory diarrhea with fever; mildly effective [1][3]
- Loperamide + simethicone combination provides faster relief of watery diarrhea and gas-related discomfort [1]
- Ondansetron for significant vomiting impairing oral rehydration [3]
Contraindicated/avoid
- Loperamide in bloody or febrile diarrhea — risk of toxic megacolon and prolonged illness [1][4]
- Antibiotics in suspected STEC (fluoroquinolones, β-lactams, TMP-SMX, metronidazole) — evidence of harm, increased HUS risk [3]
- Avoid empiric antibiotics in most uncomplicated cases [1][3]
Empiric antibiotic regimens (when indicated)
- Fluoroquinolone: ciprofloxacin 750 mg × 1 dose or 500 mg BID × 3 days; levofloxacin 500 mg × 1 dose [5-6]
- Azithromycin: 1,000 mg × 1 dose or 500 mg daily × 3 days — preferred for travel to Southeast Asia/India (fluoroquinolone-resistant Campylobacter) and as first-line for Campylobacter [3][5-6]
- Rifaximin: option for moderate, non-invasive traveler's diarrhea [7]
- Single-dose therapy is usually sufficient; 3-day course for fever or dysentery [6]
4. Diet
- Oral rehydration is the cornerstone — low-osmolarity ORS preferred (200–250 mOsm/L) [1][8]
- Early refeeding as tolerated decreases intestinal permeability and shortens illness; no specific diet required — age-appropriate regular diet is recommended [1]
- Avoid excessive sugary drinks (osmotic diarrhea worsening)
- Avoid dairy only if lactose intolerance is suspected post-infection
- Hydration with electrolyte-containing fluids; homemade ORS recipes are acceptable [1]
- Long-term: identify and avoid implicated food sources; food safety education
5. Review of Systems
- GI: nausea, vomiting, abdominal pain/cramping, tenesmus, bloating, stool frequency/character
- Constitutional: fever, chills, malaise, myalgias, weight loss
- GU: decreased urine output, dark urine (dehydration markers)
- Neuro: dizziness, lightheadedness, syncope, confusion (dehydration/sepsis)
- MSK: reactive arthritis (post-Salmonella, Shigella, Campylobacter, Yersinia)
- Heme: pallor, petechiae (consider HUS with STEC)
- Skin: rash (enteric fever, reactive arthritis)
6. Collateral History and Family History
- Collateral: shared meals or exposures among household/travel companions — suggests common-source outbreak [3]
- Institutional setting (nursing home, daycare, hospital) — norovirus, C. difficile, Shigella [3]
- Occupation: food handler, healthcare worker, childcare worker — public health reporting implications [1]
- Family history: IBD (may mimic or be unmasked by infection), immunodeficiency syndromes
- Social context: recent travel itinerary, water sources, sexual practices [3]
7. Risk Factors
- International travel to low-income countries (80–90% of traveler's diarrhea is bacterial) [2][9]
- Foodborne exposures: undercooked poultry (Campylobacter, Salmonella), ground beef (STEC), raw shellfish (Vibrio), unpasteurized dairy (Salmonella, Campylobacter, Yersinia, Listeria), raw eggs, contaminated produce [3]
- Contaminated water: recreational or drinking water [3]
- Age extremes: infants and elderly ≥65 years [1-2]
- Immunocompromise: HIV/AIDS, transplant, chemotherapy, chronic steroids [1]
- PPI use, recent antibiotic use [4]
- Institutional exposure: hospitals, nursing homes, prisons, daycare [3]
- Animal contact: petting zoos, farms [3]
8. Differential Diagnosis
Cannot-miss diagnoses
- Mesenteric ischemia — severe abdominal pain out of proportion to exam, age >50, atrial fibrillation [4]
- Appendicitis — RLQ pain (Yersinia can mimic) [3]
- Toxic megacolon — especially with C. difficile or IBD
- STEC with HUS — bloody diarrhea, thrombocytopenia, AKI, microangiopathic hemolytic anemia [3]
- Sepsis from any invasive enteric pathogen
Important alternatives
- Viral gastroenteritis (norovirus, rotavirus) — most common cause of acute diarrhea overall; typically vomiting-predominant, self-limited 2–3 days [3][8]
- C. difficile colitis — recent antibiotics, hospitalization [1]
- Inflammatory bowel disease flare — chronic history, extraintestinal manifestations [1]
- Preformed toxin food poisoning (S. aureus, B. cereus) — rapid onset <6 hours, vomiting-predominant, resolves in 24 hours [3]
- Parasitic infection (Giardia, Cryptosporidium, Cyclospora) — consider if >7 days duration [8]
- Medication-induced diarrhea (antibiotics, metformin, colchicine, SSRIs) [1]
- Radiation enteritis, celiac disease, thyroid disease [1]
9. Past Medical History
- Prior episodes of infectious diarrhea or traveler's diarrhea
- IBD (Crohn's, UC) — flares can mimic or coexist with infection
- Immunocompromising conditions: HIV, transplant, malignancy, chronic steroids
- Chronic kidney disease — higher risk from dehydration
- Cardiac disease — electrolyte derangements may be poorly tolerated
- Surgical history: prior bowel resection, bariatric surgery (altered anatomy)
- C. difficile history — recurrence risk
- Autoimmune conditions (reactive arthritis post-infection) [3]
10. Physical Exam
Vital signs
Dehydration assessment
- Dry mucous membranes, decreased skin turgor, sunken eyes, delayed capillary refill [1][10]
- Decreased urine output, altered mental status (severe) [10]
- Orthostatic hypotension — most useful bedside indicator of significant volume depletion [11]
Abdominal exam
- Diffuse tenderness (common), focal tenderness (consider surgical pathology)
- Assess for peritoneal signs (guarding, rigidity, rebound) — if present, consider perforation, appendicitis, ischemia [4]
- Distension and absent bowel sounds (toxic megacolon)
Rectal exam
General
- Rash (enteric fever — rose spots; reactive arthritis)
- Joint swelling (reactive arthritis)
11. Lab Studies
Not routinely needed for uncomplicated, self-limited watery diarrhea in immunocompetent patients [1]
Indicated when alarm features present
- Stool multiplex PCR (NAAT) — preferred over traditional culture; targets Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, Shiga toxin [1][12]
- Stool culture — required if outbreak investigation needed for public health reporting [1]
- C. difficile testing (NAAT or multistep) — if recent hospitalization >3 days or antibiotics within 12 weeks [1]
- BMP/CMP — electrolytes and renal function for dehydrated patients [1]
- CBC — leukocytosis (WBC >10,000 in ~65% of STEC O157 infections); thrombocytopenia if HUS suspected [3]
- Blood cultures — if septic, febrile with systemic toxicity, or suspected bacteremia (Salmonella, enteric fever) [1]
- Lactate — if sepsis suspected
- Peripheral smear — if HUS suspected (schistocytes)
- LDH, haptoglobin, reticulocyte count — if microangiopathic hemolytic anemia suspected
Monitoring for STEC
12. Imaging
- Not routinely indicated for uncomplicated bacterial gastroenteritis
- Abdominal CT with contrast — if concern for surgical pathology (appendicitis, diverticulitis, mesenteric ischemia, perforation, toxic megacolon, abscess) [4]
- Abdominal X-ray (KUB) — if concern for obstruction, ileus, or toxic megacolon (colonic dilation >6 cm)
- CT angiography — if mesenteric ischemia suspected (age >50, pain out of proportion, atrial fibrillation)
13. Special Tests
- Multiplex GI PCR panels (e.g., BioFire FilmArray) — rapid detection of bacterial, viral, and parasitic pathogens from a single stool specimen [12]
- Fecal lactoferrin or calprotectin — markers of intestinal inflammation; can help distinguish inflammatory from non-inflammatory diarrhea
- Ova and parasites — if diarrhea persists >7 days or travel to endemic areas [12]
- Modified acid-fast stain — for Cryptosporidium, Cyclospora, Cystoisospora [3]
- Point-of-care ultrasound (POCUS) — IVC collapsibility for volume status assessment in the ED
14. ECG
- Indicated when significant dehydration, electrolyte abnormalities, or elderly patients
- Hypokalemia findings: flattened T waves, U waves, ST depression, prolonged QT — common with profuse diarrhea
- Hypomagnesemia: prolonged QT, torsades risk
- Hyperkalemia (if AKI/HUS develops): peaked T waves, widened QRS
- Baseline ECG if ondansetron is being considered (QT prolongation risk)
- Rule out cardiac ischemia in elderly patients presenting with tachycardia and hypotension
15. Assessment
Severity stratification
- Mild: tolerable diarrhea, no fever, no blood, maintaining oral intake — supportive care only [7]
- Moderate: distressing symptoms interfering with activities, mild dehydration — consider antidiarrheals ± antibiotics if travel-related [7]
- Severe: incapacitating illness, high fever, bloody stools (dysentery), signs of sepsis, significant dehydration — requires IV fluids, stool studies, empiric antibiotics, possible admission [7]
Typical vs. atypical presentations
- Typical: acute onset watery or bloody diarrhea with cramping, fever, nausea ± vomiting
- Atypical: STEC may present with severe abdominal pain and bloody stools but minimal or no fever; Yersinia may mimic appendicitis; C. perfringens/B. cereus present primarily with vomiting [3]
Complications
- Dehydration, AKI, electrolyte derangements
- HUS (STEC — especially children and elderly)
- Bacteremia/sepsis (Salmonella, especially in extremes of age, sickle cell, immunocompromised)
- Reactive arthritis (Salmonella, Shigella, Campylobacter, Yersinia)
- Guillain-Barré syndrome (post-Campylobacter)
- Post-infectious IBS [3]
- Toxic megacolon (C. difficile, severe colitis)
16. Treatment Plan
Initial stabilization
- oral rehydration preferred[1]
Symptomatic therapy
- Loperamide 4 mg load → 2 mg after each loose stool (max 8 mg/day × 48 hours) — watery, non-bloody, afebrile diarrhea only [4]
- Bismuth subsalicylate 524 mg q30–60 min PRN (max 8 doses/day) — safe in inflammatory diarrhea [1][3]
- Ondansetron 4–8 mg IV/PO for significant vomiting [3]
Empiric antibiotics (indicated for)
- Sepsis or signs of systemic toxicity
- Moderate-to-severe traveler's diarrhea
- Bacillary dysentery (bloody stool + fever + tenesmus) presumptively Shigella
- Immunocompromised with severe illness [3]
Empiric regimens in adults
- Ciprofloxacin 500 mg PO BID × 3 days (or 750 mg × 1 dose)
- Azithromycin 500 mg PO daily × 3 days (or 1,000 mg × 1 dose) — first-line if travel to Southeast Asia/India or suspected Campylobacter [3][6]
- Rifaximin 200 mg TID × 3 days — for moderate, non-invasive traveler's diarrhea only [7]
Critical caution: Avoid antibiotics if STEC is suspected (bloody diarrhea without fever) — increased risk of HUS [3]
Targeted therapy based on culture/PCR results per organism-specific guidelines [1]
17. Disposition
Admission criteria
- Sepsis or hemodynamic instability
- Severe dehydration unresponsive to initial IV resuscitation
- Inability to tolerate oral intake despite antiemetics
- Suspected HUS (thrombocytopenia, AKI, hemolytic anemia)
- Toxic megacolon or peritoneal signs
- Significant comorbidities (elderly, immunocompromised, cardiac disease) with moderate-severe illness
- Concern for surgical abdomen
Observation indications
- Moderate dehydration requiring IV fluids with expected improvement
- Elderly or comorbid patients needing monitoring of electrolytes/renal function
Discharge criteria
- Tolerating oral fluids
- Hemodynamically stable without orthostasis
- No alarm features (no bloody stool, no high fever, no peritoneal signs)
- Reliable follow-up and ability to self-monitor
- Adequate understanding of return precautions
Specialist consultation triggers
- GI: suspected IBD, toxic megacolon, need for endoscopy
- Surgery: peritoneal signs, suspected perforation or appendicitis
- Infectious disease: immunocompromised host, unusual pathogens, treatment failure
- Nephrology: HUS with renal failure
- Public health notification for reportable pathogens (Salmonella, Shigella, STEC, Campylobacter, Listeria) [1]
18. Follow Up / Return Precautions
Follow-up timing
- Uncomplicated cases: PCP follow-up in 2–3 days if not improving, or sooner if worsening
- Patients on empiric antibiotics: reassess in 48–72 hours; adjust based on culture/PCR results
- STEC-positive patients: serial CBC and BMP to monitor for HUS for 7–10 days post-onset [3]
Return immediately for
- Bloody stools (new or worsening)
- High fever (≥38.5°C / 101.3°F)
- Inability to keep fluids down for >24 hours
- Decreased urine output, dizziness, or syncope
- Severe or worsening abdominal pain
- Confusion or altered mental status
- Signs of rash, joint swelling, or dark urine (post-infectious complications)
Patient counseling
- Most bacterial gastroenteritis resolves in 3–7 days with supportive care [1]
- Strict hand hygiene to prevent household transmission
- Food handlers should not return to work until symptom-free (per local public health guidance)
- Avoid preparing food for others while symptomatic
- Continue oral rehydration; resume normal diet as tolerated [1]
- Post-infectious IBS symptoms (bloating, altered bowel habits) may persist for weeks to months [3]
References
1. Acute Diarrhea in Adults. — Meisenheimer ES, Epstein C, Thiel D. American Family Physician. 2022.
2. Bacterial Diarrhea. — DuPont HL. The New England Journal of Medicine. 2009.
3. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. — Shane AL, Mody RK, Crump JA, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2017.
4. Acute Infectious Diarrhea in Immunocompetent Adults. — DuPont HL. The New England Journal of Medicine. 2014.
5. The Pretravel Consultation. — Rupert J, Groh T, Allen R. American Family Physician. 2025.
6. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. — Riddle MS, DuPont HL, Connor BA. The American Journal of Gastroenterology. 2016.
7. Travelers’ Diarrhea. — Bradley A. Connor and Daniel T. Leung CDC Yellow Book. 2025.
8. Viral Gastroenteritis. — Flynn TG, Olortegui MP, Kosek MN. Lancet. 2024.
9. Bacterial Travellers' Diarrhoea: A Narrative Review of Literature Published Over the Past 10 Years. — Lόpez-Vélez R, Lebens M, Bundy L, Barriga J, Steffen R. Travel Medicine and Infectious Disease. 2022.
10. Balanced Crystalloid Solutions Versus 0.9% Saline for Treating Acute Diarrhoea and Severe Dehydration in Children. — Florez ID, Sierra J, Pérez-Gaxiola G. The Cochrane Database of Systematic Reviews. 2023.
11. Is This Patient Hypovolemic?. — McGee S, Abernethy WB, Simel DL. The Journal of the American Medical Association. 1999.
12. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.