Gastroenteritis
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Gastroenteritis
Definition
Gastroenteritis is an acute diarrheal infection of the gastrointestinal tract. It is generally self-limited, with most patients experiencing nausea, vomiting, and diarrhea (diarrhea being the predominant symptom). Diarrhea is defined as passage of 3+ unformed liquid stools per day, or >250 g/day. Dysentery specifically refers to colonic inflammation producing bloody, mucus-containing diarrhea with fever, abdominal pain, and tenesmus.
- Rosen's Emergency Medicine, p. 1300
Epidemiology
-
~180 million cases of acute diarrhea occur annually in the United States; most are self-limited
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Diarrheal diseases are the second leading cause of death worldwide in children outside the neonatal period
-
Norovirus is the most common cause in adults and children (in countries with rotavirus vaccination programs); Rotavirus dominates where vaccination is absent
-
Viruses account for the majority of infectious cases overall
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Incidence is rising due to international travel, mass food production, and increased consumption of raw produce
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In developed countries, deaths occur most often in the elderly; C. difficile and norovirus are most frequently implicated
-
Tintinalli's Emergency Medicine, p. 886; Rosen's Emergency Medicine, p. 1301
Classification by Duration
| Type | Duration | Typical Cause |
|---|---|---|
| Acute | <7 days | Viral, bacterial |
| Prolonged | 7-13 days | Viral, bacterial |
| Persistent | 14-29 days | Protozoan, parasitic |
| Chronic | >30 days | Parasites, non-infectious conditions |
Pathophysiology
Four main mechanisms drive GI fluid loss:
- Ingestion of preformed toxins (e.g., Staph aureus, B. cereus, C. perfringens) - rapid onset 1-6 hours post-ingestion
- Adherence of pathogens to intestinal cell walls
- Mucosal invasion (e.g., Shigella, Salmonella, Campylobacter) - invades large intestine, causes inflammatory diarrhea
- Enterotoxin / cytotoxin production - enterotoxins bind mucosal receptors, increasing cAMP/cGMP, causing secretory diarrhea (e.g., ETEC, V. cholerae)
Each pathway leads to increased fluid secretion or decreased absorption, resulting in diarrhea. Fasting worsens bowel capacity to absorb fluids; continued feeding improves mucosal recovery.
Viral pathogens (rotavirus, adenovirus) invade small intestinal villous epithelium, destroying mature absorptive cells and causing osmotic diarrhea through carbohydrate malabsorption.
- Tintinalli's Emergency Medicine, p. 885; Rosen's Emergency Medicine, p. 1301
Causative Organisms
Viral (most common overall)
- Norovirus - most common cause in all ages in developed countries
- Rotavirus - most common in unvaccinated children
- Adenovirus (enteric types 40/41)
Bacterial
| Organism | Key Features |
|---|---|
| Campylobacter jejuni | #1 or #2 culture-proven bacterial cause in developed countries |
| Salmonella | #1 or #2 culture-proven; avoid antibiotics in non-severe cases (prolongs shedding) |
| Shigella | Dysentery, seizures, HUS; treat if symptoms warrant |
| ETEC | Most common cause of traveler's diarrhea |
| STEC / E. coli O157:H7 | Watery → bloody diarrhea; NO antibiotics (increases HUS risk) |
| Vibrio cholerae | Profuse watery diarrhea; treat with doxycycline |
| C. difficile | Post-antibiotic; treat with vancomycin or fidaxomicin |
| Staph aureus, B. cereus, C. perfringens | Food poisoning; supportive care only |
| Yersinia enterocolitica | Mimics appendicitis (right lower quadrant pain) |
Parasitic
- Giardia - most common parasitic cause; foul-smelling, prolonged diarrhea; treat with metronidazole
- Cryptosporidium, Cyclospora, Isospora - especially in immunocompromised (HIV/CD4 <200)
E. coli groups causing gastroenteritis
| E. coli Type | Site | Disease | Mechanism |
|---|---|---|---|
| ETEC | Small intestine | Traveler's/infant diarrhea; watery | ST/LT enterotoxins - hypersecretion |
| EPEC | Small intestine | Infant diarrhea | Attachment/effacement (A/E) lesions |
| EAEC | Small intestine | Persistent watery diarrhea | Aggregative adherence, microvillus damage |
| STEC | Large intestine | Bloody diarrhea (hemorrhagic colitis) → HUS | Shiga toxins (Stx1, Stx2) |
| EIEC | Large intestine | Dysentery | Plasmid-mediated mucosal invasion |
- Medical Microbiology 9e, p. 298; Rosen's Emergency Medicine, p. 1300-1302
Clinical Features
Typical symptoms: nausea, vomiting, diarrhea (often watery), abdominal cramping, low-grade fever
Red flags suggesting bacterial / serious disease:
- High fever
- Bloody or mucus-containing stool (dysentery)
- Severe dehydration
- Peritoneal signs (consider appendicitis)
- Tenesmus, rectal pain
Duration: Viral gastroenteritis typically lasts <7 days and not longer than 14 days.
Dehydration Assessment (Clinical Dehydration Score):
| Score | Appearance | Eyes | Mucosa | Tears |
|---|---|---|---|---|
| 0 | Normal | Normal | Moist | Normal |
| 1 | Thirsty, restless/irritable | Mildly sunken | Sticky | Decreased |
| 2 | Drowsy/limp/cold/diaphoretic | Very sunken | Dry | Absent |
Score >0 = some dehydration; score >5 = moderate-severe dehydration
Laboratory Testing
- Routine lab testing and stool cultures are NOT indicated for most patients
- Obtain CBC, electrolytes, stool cultures in:
- Ill-appearing patients
- Bloody diarrhea
- Fever + systemic signs
- Suspected C. difficile
- Immunocompromised patients
- Neonates, infants, elderly
- Measure serum glucose in infants (hypoglycemia in up to 9% of pediatric cases)
- WBC and CRP are not reliable for distinguishing viral from bacterial gastroenteritis
- STEC confirmation: sorbitol-MacConkey agar + Shiga toxin immunoassay or PCR
- C. difficile: stool toxin assay or PCR
Treatment
1. Rehydration (cornerstone of treatment)
Oral Rehydration Therapy (ORT) is the first-line treatment recommended by WHO, AAP, and ESPGHAN:
- Works via coupled Na+/glucose co-transport at intestinal brush border (remains intact even in severe diarrhea)
- WHO reduced-osmolarity ORS (2002): Na 75 mmol/L, Glucose 75 mmol/L, K 20 mmol/L, osmolarity 245 mOsm/L
- North American commercial solutions (Pedialyte, Enfalyte): 45-60 mmol/L sodium
- Avoid: fruit juices, sports drinks, tea, soda - excessive sugar worsens losses; insufficient sodium
IV rehydration is indicated for:
- Severe dehydration or hemodynamic compromise
- Altered mental status precluding safe oral intake
A Cochrane review showed no difference between ORT and IV in rehydration failure or weight gain; ORT is associated with shorter hospital stay.
2. Antiemetics
- Ondansetron 0.15 mg/kg (up to 8 mg) PO or IV - safe, cost-effective, helps facilitate ORT
3. Diet
- Early resumption of normal feeding is advised
- Continue breastfeeding in infants
- No need for special diets (BRAT diet is no longer recommended)
- Good nutrition promotes mucosal recovery
4. Antimotility agents
- Use with caution in fever or bloody diarrhea - increases toxin/pathogen contact time
- If used in these settings, combine with antibiotics
5. Antibiotic Therapy (selective)
| Pathogen | Treatment |
|---|---|
| Shigella | Ciprofloxacin 500 mg PO BID x3 days; OR azithromycin 500 mg PO daily x3 days |
| Salmonella typhi | Ciprofloxacin 500 mg PO BID x7d; or azithromycin 500 mg daily x7d; or IV ceftriaxone 1-2 g daily x7d |
| Salmonella nontyphi | No treatment in non-severe cases; levofloxacin 500 mg x7-10d if severe |
| Campylobacter jejuni | Azithromycin 500 mg PO daily x3d; or erythromycin 500 mg BID x5d |
| ETEC (traveler's diarrhea) | Ciprofloxacin 500 mg BID x3d; rifaximin 200 mg TID x3d; or azithromycin 1g PO once |
| STEC / E. coli O157:H7 | NO antibiotics - increases HUS/TTP risk |
| V. cholerae | Doxycycline 4-6 mg/kg up to 300 mg PO daily x3d |
| C. difficile | Vancomycin 125 mg PO QID x10d OR fidaxomicin 200 mg PO BID x10d; alternative: metronidazole 500 mg TID x10d |
| Giardia | Metronidazole + rehydration |
- Rosen's Emergency Medicine, p. 1003-1023; Tintinalli's Emergency Medicine, p. 316-319
Special Populations
Immunocompromised (HIV, CD4 <200): Increased risk from CMV, Cryptosporidium, Cyclospora, Isospora, MAC, and Giardia
Elderly: Highest morbidity and mortality; C. difficile and norovirus are leading causes of fatal diarrheal illness in this group
Infants and neonates: High risk of rapid dehydration; monitor glucose; age <3 months with fever/diarrhea warrants early investigation
Traveler's diarrhea: ETEC is the most common cause (~80% of cases are bacterial); usually self-limited; fluoroquinolones, rifaximin, or azithromycin are options
C. difficile - Special Considerations
- Risk factors: recent antibiotics (1-4 weeks), hospitalization, long-term care, solid organ transplant, proton pump inhibitor use
- Diagnosis: stool toxin assay or PCR
- Treat with vancomycin 125 mg PO QID x10d (first-line) or fidaxomicin
- Obtain abdominal CT for toxic megacolon / pseudomembranous colitis if: older patient, septic appearance, tender distended abdomen, or high leukocytosis
Prevention
- Hand hygiene with soap and water or hand sanitizer
- Rotavirus vaccination in infants (reduces severity and hospitalization)
- Safe food handling and water treatment
- Surveillance reporting to health authorities during outbreaks
Sources:
- Tintinalli's Emergency Medicine: A Comprehensive Study, Chapter 131
- Rosen's Emergency Medicine: Concepts and Clinical Practice, Chapter 80
- Medical Microbiology 9e, Chapter 25
- Goldman-Cecil Medicine
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