Gastroenteritis refers to inflammation of the stomach and intestines, most commonly manifesting with abdominal pain, diarrhea, nausea, vomiting, and sometimes fever. It’s a very common condition worldwide and is typically self-limited, but can cause significant dehydration—particularly in young children, older adults, and immunocompromised individuals. Etiologies include a wide range of pathogens (viruses, bacteria, parasites), as well as noninfectious causes (toxic ingestions, medications).
1. Etiologic Agents
1.1 Viral Causes (Most Common)
1.2
Norovirus
Single-stranded RNA virus of the Caliciviridae family.
Leading cause of acute gastroenteritis outbreaks in all age groups (cruise ships, schools, nursing homes).
Incubation: 12–48 hours; illness lasts 24–72 hours.
Rotavirus
Reovirus family, double-stranded RNA.
Historically the most common cause of severe diarrhea in infants and young children; vaccine programs have greatly reduced incidence.
Incubation: ~2 days; illness lasts 3–8 days.
Adenovirus (serotypes 40/41)
Often causes diarrhea in young children; sometimes associated with concurrent respiratory symptoms.
Incubation: 8–10 days; diarrhea may persist longer (up to 2 weeks).
Astrovirus
Affects primarily infants and young children; tends to cause mild, self-limited diarrhea.
Sapovirus
Similar to norovirus but less common; can affect all ages.
1.3 Bacterial Causes
1.4
Enterotoxigenic Escherichia coli (ETEC)
Common cause of “traveler’s diarrhea” in developing regions.
Produces heat-labile and/or heat-stable toxins → secretory diarrhea.
Campylobacter jejuni
Frequent cause of bacterial foodborne gastroenteritis (undercooked poultry, unpasteurized milk).
Fever, crampy abdominal pain (often right lower quadrant), and often bloody diarrhea.
Salmonella spp. (non-typhoidal)
Often linked to poultry, eggs, and reptiles.
Presents with fever, abdominal cramps, and diarrhea (sometimes bloody).
Shigella spp.
Highly contagious; low infective dose.
Presents with high fever, abdominal cramping, and frequent small-volume bloody, mucoid stools.
Shiga-toxin–producing E. coli (STEC), particularly O157:H7
Undercooked ground beef, unpasteurized dairy.
Bloody diarrhea; risk of hemolytic uremic syndrome (HUS), especially in children.
Vibrio cholerae
Toxin-mediated secretory diarrhea (“rice-water stools”).
Endemic in areas with poor sanitation; can cause profuse diarrhea and rapid dehydration.
Clostridioides difficile
Often follows broad-spectrum antibiotic use.
Presents with watery diarrhea, abdominal pain, leukocytosis; severe cases can lead to pseudomembranous colitis.
1.3 Parasitic Causes
Giardia lamblia
Foul-smelling, greasy stools; often from contaminated water sources.
Subacute onset, prolonged illness (weeks).
Entamoeba histolytica
Dysentery with blood and mucus; risk of liver abscess.
Endemic in areas with poor sanitation.
Cryptosporidium parvum
Watery diarrhea; particularly severe and prolonged in immunocompromised hosts (e.g., AIDS).
Often waterborne outbreaks.
Cyclospora cayetanensis
Prolonged, relapsing diarrhea; associated with fresh produce (berries, basil).
Isospora belli
Causes chronic diarrhea in immunocompromised individuals.
1.5 Noninfectious Causes
1.6
Medications:
Antibiotics (e.g., causing C. difficile overgrowth)
NSAIDs, antineoplastics, chemotherapy agents
Toxins:
Scombroid poisoning (histamine in spoiled fish)
Staphylococcal enterotoxin (rapid-onset vomiting from contaminated foods)
Bacillus cereus (two types: emetic [rice], diarrheal [meats/vegetables])
Inflammatory conditions:
Inflammatory bowel disease flares (e.g., Crohn’s disease, ulcerative colitis)
Ischemic colitis
Radiation enteritis
Malabsorption syndromes (e.g., lactose intolerance, celiac disease)
2. Epidemiology & Risk Factors
Global burden: Acute diarrheal diseases remain a leading cause of morbidity and mortality worldwide, particularly in children under 5.
Seasonality: Viral gastroenteritis (e.g., norovirus, rotavirus) often peaks in cooler months; bacterial causes more frequent in warmer months when food spoilage risk is higher.
Settings of outbreaks:
Closed or semi-closed communities (cruise ships, nursing homes, daycare centers).
Institutions: schools, hospitals.
Community clusters after contaminated food or water supplies.
High-risk populations:
Infants and young children (immature immunity, greater dehydration risk)
Elderly (reduced physiological reserve)
Immunocompromised (e.g., HIV/AIDS, chemotherapy, transplant recipients)
Travelers to endemic regions (“traveler’s diarrhea”)
Transmission:
1. Fecal–oral route: Person-to-person spread by inadequate handwashing.
2. Contaminated food or water: Improperly cooked meats, eggs, dairy, untreated water sources.
3. Environmental surfaces: Shared utensils, toys, restroom surfaces—especially for viruses like norovirus.
4. Pathophysiology
1. Disruption of intestinal lining: Pathogens adhere to, invade, or release toxins that affect enterocytes or the lamina propria.
2. Altered ion transport:
Toxin-mediated (secretory) diarrhea: e.g., cholera toxin, ETEC heat-labile toxin, norovirus → toxin binds to enterocyte receptors → upregulates cyclic AMP or cyclic GMP → chloride and water secretion into the lumen.
Inflammatory (exudative) diarrhea: e.g., Shigella, Salmonella, Campylobacter → invade mucosa, elicit neutrophilic response → damage to villous architecture, blood and pus in stool.
3. Malabsorption: Damage to villi (often viral) → decreased surface area for absorption → osmotic diarrhea.
4. Motility changes: Some infections (e.g., enteroinvasive organisms) can increase peristalsis, reducing contact time for absorption.
5. Clinical Presentation
4.1 Common Symptoms
4.2
Diarrhea:
Watery/secretory: Large volume, nonbloody; no reduction with fasting (e.g., cholera, ETEC, viral).
Inflammatory/exudative: Smaller volume, often with blood, mucus, or pus; associated with fever and tenesmus (e.g., Shigella, EHEC, Campylobacter).
Nausea and vomiting: Particularly prominent with viral causes (norovirus, rotavirus) or preformed toxins (Staph aureus, Bacillus cereus emetic type).
Abdominal pain and cramping: Diffuse or localized; may mimic appendicitis in Campylobacter (right lower quadrant).
Fever: Common with invasive bacterial causes (e.g., Salmonella, Shigella, Campylobacter); less so with purely toxin-mediated illnesses.
Systemic symptoms: Headache, myalgias, malaise—especially with viral gastroenteritis.
4.3 Red Flags (Require Immediate Attention)
4.4
Signs of severe dehydration:
Tachycardia, hypotension, dry mucous membranes, sunken eyes, decreased skin turgor, oliguria (urine output <0.5 mL/kg/hr).
Bloody diarrhea with high fever: Suggestive of invasive bacterial infection or EHEC (risk of HUS).
Evidence of sepsis: Altered mental status, significant hypotension, high or very low white blood cell count.
Persistent vomiting: Inability to tolerate oral rehydration → risk of rapid dehydration.
Prolonged illness (>7–10 days): Raises suspicion for parasitic infection (Giardia, Cryptosporidium) or inflammatory bowel disease.
Neurologic findings (confusion, lethargy): Possible electrolyte disturbances or severe systemic infection.
5. Diagnostic Evaluation
5.1 Initial Assessment
5.2
History:
Onset and duration of symptoms; progression of diarrhea (watery vs. bloody).
Recent travel or known outbreaks.
Food history: raw or undercooked meats, shellfish, unpasteurized dairy, recent picnics/restaurant meals.
Exposure to sick contacts (family, daycare, institutional).
Medication history: antibiotics, immunosuppressants.
Underlying medical conditions: immunodeficiency, chronic liver disease, inflammatory bowel disease.
Physical Exam:
Assess hydration status (mucous membranes, skin turgor, capillary refill, orthostatic vital signs).
Abdominal examination: tenderness, guarding (rule out perforation), rebound.
Check for signs of systemic infection (fever, tachycardia).
5.3 Laboratory and Microbiological Testing
5.4
When to obtain stool studies:
Severe diarrhea (≥6 unformed stools/24 hours).
Bloody stools, high fever, signs of sepsis.
Recent antibiotic use (suspect C. difficile).
Persistent symptoms >7 days.
Immunocompromised hosts.
Stool Studies:
1. Routine stool culture: Detects Salmonella, Shigella, Campylobacter, Shiga-toxin E. coli.
2. PCR-based multiplex panels: Simultaneously identify viruses, bacteria, and parasites with high sensitivity.
3. Ova and parasite examination: Especially if diarrhea is prolonged (>10 days) or travel to endemic regions.
4. Clostridioides difficile toxin assay: When there is history of antibiotic use or healthcare exposure.
5. Fecal leukocytes or fecal lactoferrin: Indicate inflammatory diarrhea; not specific but help triage.
Blood Tests:
CBC: Leukocytosis suggests bacterial invasion; leukopenia may occur in severe viral infections.
Electrolytes and renal function: Assess dehydration severity (e.g., elevated BUN, creatinine).
Serologies: Rarely used for acute diagnosis; sometimes used for special pathogens (e.g., Entamoeba).
Imaging (if indicated):
Abdominal ultrasound: Evaluate for complications (intussusception in infants, biliary pathology).
Abdominal X-ray: Rule out toxic megacolon if suspect fulminant C. difficile or IBD flare.
CT abdomen: Evaluate for complications (abscess, obstruction, ischemia) when clinical suspicion is high.
6. Management
6.1 General Principles
6.2
1. Fluid and Electrolyte Replacement (cornerstone)
Oral Rehydration Therapy (ORT): Oral rehydration solutions (ORS) containing balanced glucose and electrolytes should be first-line for mild to moderate dehydration.
Intravenous Fluids: Indicated for moderate to severe dehydration, persistent vomiting, or inability to tolerate ORT. Common regimens include isotonic crystalloids (e.g., normal saline) with careful monitoring of electrolytes and urine output.
2. Nutritional Support
Early refeeding is encouraged once vomiting subsides; bland, easily digestible foods (e.g., rice, bananas, toast) can be reintroduced.
BRAT diet (Bananas, Rice, Applesauce, Toast) is sometimes recommended temporarily, but avoidance of full-fat dairy and high-fiber foods is often advised until symptoms improve.
Breastfeeding or formula feeding should continue in infants; consider temporary switching from lactose-containing formula if lactose intolerance develops.
3. Symptomatic Relief
Antiemetics: Ondansetron is commonly used to control nausea/vomiting, especially in children, to ensure successful ORT.
Antipyretics/Analgesics: Acetaminophen or ibuprofen for fever and cramps (ensure adequate hydration).
Antidiarrheals (use with caution):
Loperamide: Can reduce stool frequency in mild, non-bloody diarrhea; contraindicated if fever >38.5 °C or bloody stools (risk of prolonging invasive infection).
Bismuth subsalicylate: May reduce stool frequency and duration if used early in uncomplicated cases; avoid in children (Reye’s syndrome risk).
6.3 Targeted Antimicrobial Therapy
6.4
Viral Gastroenteritis
No specific antivirals for most agents (e.g., norovirus, rotavirus). Treatment remains supportive.
In immunocompromised patients with chronic norovirus, nitazoxanide has been used off-label in select cases.
Rotavirus vaccination in infancy is the main preventive strategy.
Bacterial Gastroenteritis
Empiric Antibiotics: Often not indicated unless severe disease, risk for invasive infection, or specific pathogens suspected.
Preferred Agents (guided by local resistance):
Campylobacter: Azithromycin 500 mg once daily for 3 days (children: 10 mg/kg once daily); fluoroquinolones if susceptible.
Shigella: Azithromycin or trimethoprim-sulfamethoxazole (depending on sensitivity).
Salmonella (non-typhoidal): Usually self-limited; treat only if high-risk (infants <3 months, elderly, immunocompromised) with fluoroquinolones or third-generation cephalosporins.
ETEC (traveler’s diarrhea): A single dose of azithromycin (1 g) or a fluoroquinolone for adults; rifaximin (550 mg twice daily for 3 days) in certain regions.
Vibrio cholerae: Doxycycline 300 mg single dose; alternatives: azithromycin, tetracycline.
C. difficile: First-line therapy is oral vancomycin (125 mg four times daily for 10 days) or fidaxomicin. Metronidazole is no longer preferred except if neither is available.
Parasitic Infections
Giardia lamblia: Metronidazole 250 mg three times daily for 5–7 days (children: 15 mg/kg/day in divided doses). Tinidazole single dose is an alternative.
Entamoeba histolytica: Metronidazole 750 mg three times daily for 5–10 days, followed by a luminal agent (e.g., paromomycin) to eradicate cysts.
Cryptosporidium: Nitazoxanide 500 mg twice daily for 3 days in immunocompetent hosts; supportive care is mainstay in immunocompromised.
Cyclospora: Trimethoprim-sulfamethoxazole (160/800 mg) twice daily for 7–10 days.
7. Prevention
7.1 Hand Hygiene
7.2
Proper Handwashing: Wash with soap and water for at least 20 seconds after toilet use, diaper changes, and before preparing or eating food.
Alcohol-Based Hand Sanitizers: Effective against many pathogens but less so against norovirus and C. difficile spores—soap and water preferred when diarrhea is present.
7.3 Food and Water Safety
7.4
Cook Foods Thoroughly: Ensure poultry reaches an internal temperature of ≥74 °C; ground beef ≥71 °C.
Avoid Raw or Undercooked Foods: Eggs, seafood (especially shellfish), unpasteurized dairy products.
Wash Fruits and Vegetables: Rinse under running water; consider peeling if safety is uncertain.
Separate Raw and Cooked Foods: Use different cutting boards and utensils to prevent cross-contamination.
Safe Water Practices:
Drink treated or boiled water in areas with questionable water quality.
Avoid ice cubes made from untested sources.
Use bottled or boiled water for brushing teeth when traveling in high-risk regions.
7.3 Vaccination
Rotavirus Vaccines (RV1, RV5): Oral live attenuated vaccines given in infancy to prevent severe rotavirus diarrhea.
Cholera Vaccines: Oral inactivated vaccines (e.g., Dukoral, Shanchol) for travelers to endemic areas, or in outbreak settings.
Typhoid Vaccines: For prevention of typhoid fever (Salmonella Typhi) in high-risk travelers; do not prevent non-typhoidal Salmonella gastroenteritis.
Norovirus Vaccines: Currently under development; not yet widely available.
7.5 Infection Control in Institutional Settings
7.6
Isolation Precautions: Use contact precautions (gowns, gloves) for patients with suspected or confirmed infectious diarrhea.
Environmental Cleaning: Disinfect surfaces with bleach-based solutions (effective against norovirus and C. difficile spores).
Cohorting and Staffing: Group infected patients together; restrict ill staff from food handling or patient care until symptom-free for at least 48 hours.
Outbreak Management: Prompt identification of source, halting communal activities (e.g., daycare, cruise services), notifying public health authorities.
8. Special Populations
Infants and Young Children
Rapidly progress to dehydration; may present with irritability, decreased urine output, sunken fontanelle.
Breastfeeding should continue; small, frequent feeds; consider lactose-free formula if risk of transient lactose intolerance.
Avoid antidiarrheals; focus on ORT and monitoring.
Elderly
May have blunted fever response and atypical presentations (e.g., confusion, weakness rather than prominent gastrointestinal symptoms).
Higher risk of severe dehydration and complications (e.g., acute kidney injury).
Pregnant Women
Certain pathogens (Listeria monocytogenes, Salmonella) can cross the placenta; higher risk of preterm labor or fetal loss.
Avoid high-risk foods (unpasteurized dairy, deli meats unless heated).
Use pregnancy-safe antibiotics when indicated (e.g., azithromycin rather than fluoroquinolones).
Immunocompromised Individuals
More prone to prolonged or severe infections (e.g., chronic Cryptosporidium in AIDS).
Lower threshold for diagnostic testing and empiric therapy.
May require hospitalization for IV fluids and targeted antimicrobials.
9. Complications
1. Dehydration
Can progress rapidly, leading to hypotension, tachycardia, electrolyte imbalances (hyponatremia, metabolic acidosis), acute kidney injury.
2. Electrolyte Disturbances
Hypokalemia (due to GI losses) can cause muscle weakness, arrhythmias.
Hyponatremia from free water losses; monitor sodium closely if high-volume diarrhea.
3. Hemolytic Uremic Syndrome (HUS)
Classically follows STEC (O157:H7) infection—triad of microangiopathic hemolytic anemia, thrombocytopenia, acute kidney injury.
Management is supportive; avoid antibiotics and antimotility agents in suspected STEC.
4. Reactive Arthritis
Can develop 1–4 weeks after infection with Campylobacter, Salmonella, Shigella, or Yersinia.
Presents with asymmetric oligoarthritis, conjunctivitis, urethritis; associated with HLA-B27 positivity.
5. Severe Systemic Infection
Invasive Salmonella (bacteremia), Shigella (sepsis), or Yersinia (mesenteric adenitis) can lead to focal infections (abscesses, osteomyelitis).
6. Pseudomembranous Colitis
From C. difficile overgrowth → severe diarrhea, abdominal pain, fever, leukocytosis; risk of toxic megacolon.
7. Malabsorption Syndromes
Postinfectious lactose intolerance (transient) due to brush border enzyme loss—usually resolves in a few weeks.
10. Prognosis
Acute viral gastroenteritis: Most individuals recover completely within 2–7 days with supportive care. Mortality is rare in healthy hosts.
Bacterial gastroenteritis: Most noninvasive bacterial causes also resolve within 5–7 days, though antibiotic-treated cases typically shorten duration by 1–2 days. Mortality remains low except in vulnerable populations or severe sepsis.
Parasitic infections: Duration can be weeks to months without targeted therapy; prompt treatment generally leads to full recovery.
Complications: With appropriate management—early rehydration, correct antimicrobial use, and monitoring—serious complications (HUS, sepsis, organ failure) remain uncommon in most settings.
11. Key Takeaways
Hydration is Crucial: Early and adequate fluid and electrolyte replacement underpins all management.
Hand Hygiene and Food Safety: Simple measures (handwashing, proper cooking, safe water) prevent most cases.
Judicious Use of Antibiotics: Empiric antibiotics are not indicated for mild, uncomplicated diarrhea—use them only when risk factors for invasive bacterial disease exist or specific pathogens are identified.
Be Alert for Red Flags: Persistent high fever, bloody stools, severe dehydration, or signs of systemic toxicity warrant prompt evaluation and, often, hospitalization.
Vaccine Prevention: Rotavirus vaccination in infancy has substantially reduced severe pediatric gastroenteritis; cholera and typhoid vaccines play roles in endemic or outbreak settings.
Tailor Management to the Patient: Consider age, comorbidities, travel history, and local resistance patterns when selecting diagnostic tests and therapies.
By recognizing the common causes, clinical patterns, and management principles—especially early rehydration—most ep
