Diagnosis and Treatment of Acute Gastroenteritis
This 22-year-old patient has acute gastroenteritis, and the immediate priority is oral rehydration solution (ORS) administered in small, frequent volumes (50-100 mL/kg over 2-4 hours) to correct dehydration, followed by replacement of ongoing losses and early resumption of normal diet. 1, 2
Diagnosis
The clinical presentation of frequent watery stools with vomiting in a previously healthy young adult is characteristic of acute gastroenteritis. 2
Viral gastroenteritis is the most likely diagnosis, accounting for the majority of cases in immunocompetent adults with watery diarrhea, fever, and vomiting. 2 Common viral pathogens include rotavirus, norovirus, and adenovirus. 3
Key Diagnostic Features to Assess:
- Watery diarrhea without blood suggests viral or enterotoxigenic bacterial etiology rather than invasive bacterial infection. 2
- Presence of vomiting with diarrhea strongly supports viral gastroenteritis or toxin-mediated food poisoning. 2, 4
- Absence of high fever (>38.5°C) or bloody stools makes bacterial dysentery (Shigella, Campylobacter, enterohemorrhagic E. coli) less likely. 2
When to Consider Alternative Diagnoses:
- Bloody diarrhea with high fever would suggest invasive bacterial pathogens requiring stool culture. 2
- Rapid onset within 1-6 hours of eating suggests preformed toxin from Staphylococcus aureus or Bacillus cereus. 2
- Watery diarrhea mistaken for gastroenteritis can occur with incomplete small bowel obstruction—however, the presence of vomiting with watery stools does not exclude gastroenteritis. 5
Diagnostic Testing:
Stool cultures and laboratory testing are not routinely needed for immunocompetent adults with acute watery diarrhea and vomiting. 2 Testing should be reserved for bloody diarrhea, symptoms lasting >5 days, immunocompromise, or severe dehydration requiring hospitalization. 2
Treatment
Immediate Rehydration (First Priority)
Assess dehydration severity through clinical examination:
- Mild dehydration (3-5% deficit): Slightly dry mucous membranes, normal vital signs, thirst. 1
- Moderate dehydration (6-9% deficit): Dry mucous membranes, decreased skin turgor, orthostatic changes, reduced urine output. 1, 4
- Severe dehydration (≥10% deficit): Altered mental status, prolonged capillary refill (>2 seconds), cool extremities, rapid deep breathing, signs of shock. 1, 4
For mild to moderate dehydration, administer low-osmolarity ORS:
- Initial rehydration: 50-100 mL/kg (approximately 3,700 mL for a 70 kg adult) over 2-4 hours. 1, 4
- Start with small volumes (5-10 mL every 1-2 minutes) if vomiting is prominent, gradually increasing as tolerated. 1
- Replace ongoing losses continuously: 10 mL/kg for each watery stool and 2 mL/kg for each vomiting episode. 1, 4
- Reassess after 2-4 hours: If still dehydrated, re-estimate deficit and continue rehydration. 1
ORS is superior to sports drinks or juices, which contain excessive simple sugars that can worsen diarrhea through osmotic effects. 5, 1
Intravenous Rehydration (When Oral Fails)
Reserve IV fluids for:
- Severe dehydration with shock. 1, 4
- Persistent vomiting despite small-volume ORS administration. 1
- Altered mental status. 1
- Failure of oral rehydration after appropriate trial. 1
Use isotonic fluids (normal saline or lactated Ringer's) in 20 mL/kg boluses until perfusion normalizes, then transition to ORS. 1, 4
Antiemetic Therapy
Ondansetron may be considered to facilitate oral rehydration if vomiting is significant and preventing adequate ORS intake. 1, 4 Typical adult dosing is 4-8 mg orally or IV. This can reduce the need for IV fluids and hospitalization. 6
Nutritional Management
Resume normal, age-appropriate diet immediately during or after rehydration—do not fast or restrict diet. 5, 1 Early refeeding reduces illness severity and duration. 1
Avoid these foods during acute illness:
- High simple sugar foods (soft drinks, undiluted fruit juices) that worsen diarrhea through osmotic effects. 1
- Fatty or heavy meals that may be poorly tolerated. 5
- Caffeinated beverages (coffee, tea, energy drinks, cola) that stimulate intestinal motility and worsen diarrhea. 1
Small, light meals guided by appetite are appropriate. 5
Pharmacological Management
Loperamide (2 mg after each loose stool, maximum 16 mg/day) may be used in immunocompetent adults with watery diarrhea once adequately hydrated. 5, 1 However, it should never be used if bloody diarrhea or high fever is present. 1
Antimicrobials are NOT indicated for typical viral gastroenteritis with watery diarrhea. 5, 1, 2 Antibiotics should only be considered for bloody diarrhea, high fever, immunocompromise, or symptoms persisting >5 days. 2
Probiotics may reduce symptom severity and duration in both adults and children, though evidence is mixed. 1
Avoid antimotility agents, adsorbents, antisecretory drugs, and toxin binders as they lack demonstrated effectiveness. 1
Infection Control
Implement strict hygiene measures:
- Hand hygiene after toilet use, before eating, and after handling soiled items. 1
- Clean and disinfect contaminated surfaces promptly. 1
- Isolate from others until at least 2 days after symptom resolution. 1
Common Pitfalls to Avoid
- Do not delay rehydration while awaiting diagnostic tests—begin ORS immediately. 1, 2
- Do not use sports drinks or apple juice as primary rehydration for moderate dehydration—use proper ORS. 1
- Do not prescribe empiric antibiotics for uncomplicated watery diarrhea without specific indications. 2
- Do not restrict diet unnecessarily—early refeeding is beneficial. 5, 1
- Do not give loperamide if bloody diarrhea or high fever is present, as this may worsen outcomes in invasive bacterial infections. 1
When to Seek Urgent Medical Care
Immediate evaluation is needed for: