In an otherwise healthy adult with sudden onset vomiting and watery diarrhea lasting less than seven days, is the likely diagnosis acute gastroenteritis rather than gastritis?

Gastritis vs Gastroenteritis: Clinical Distinction

In an otherwise healthy adult presenting with sudden onset vomiting and watery diarrhea lasting less than seven days, the diagnosis is acute gastroenteritis, not gastritis. Gastritis refers to inflammation of the stomach lining and typically presents with epigastric pain, nausea, and sometimes vomiting—but not diarrhea. The combination of vomiting and watery diarrhea is the hallmark of acute gastroenteritis. 1

Key Distinguishing Features

Acute Gastroenteritis Presentation

• Acute gastroenteritis is defined by the passage of 3 or more loose or liquid stools per 24 hours, often accompanied by vomiting, and lasting less than 7 days in the acute phase. 1
• The clinical syndrome includes both upper GI symptoms (nausea, vomiting) and lower GI symptoms (watery diarrhea), reflecting involvement of the entire gastrointestinal tract. 1
• Constitutional symptoms such as fatigue, low-grade fever, abdominal cramping, and urgency are common. 1
• Viral pathogens (particularly norovirus in adults) account for the majority of cases, making this a self-limited illness in immunocompetent patients. 1

Gastritis Presentation (What This Is NOT)

• Gastritis presents primarily with epigastric pain or discomfort, nausea, and sometimes vomiting, but diarrhea is not a feature. 2
• Symptoms are localized to the upper abdomen and reflect stomach inflammation rather than small bowel or colonic involvement. 2
• When diarrhea is present alongside upper GI symptoms, the diagnosis shifts to gastroenteritis (inflammation extending beyond the stomach). 1

Diagnostic Approach

Clinical Assessment Priorities

• Evaluate hydration status through skin turgor, mucous membrane moisture, mental status, capillary refill time, and urine output to categorize dehydration as mild (3-5%), moderate (6-9%), or severe (≥10%). 3, 4
• Assess for red-flag features that would alter management: bloody stools with fever (suggesting bacterial dysentery), severe dehydration requiring IV therapy, or immunocompromised status. 1
• Most cases of acute watery diarrhea with vomiting in immunocompetent adults do not require stool cultures or laboratory workup. 5

When to Pursue Diagnostic Testing

• Reserve stool cultures and laboratory evaluation for patients with bloody diarrhea, high fever (>38.5°C), severe dehydration, symptoms persisting beyond 7 days, recent international travel, or immunosuppression. 1, 5
• Routine diagnostic testing in typical viral gastroenteritis is unrevealing and wastes resources. 2

Management Algorithm

Rehydration as First-Line Therapy

• Oral rehydration solution (ORS) is the cornerstone of treatment for mild-to-moderate dehydration, with success rates exceeding 90% when administered correctly. 3
• Administer 2-4 liters of low-osmolarity ORS over 3-4 hours for adults with moderate dehydration, using small frequent volumes (5-10 mL every 1-2 minutes initially) to avoid triggering vomiting. 3, 4
• Replace ongoing losses with approximately 200-400 mL ORS after each watery stool. 3

Severe Dehydration Requiring IV Therapy

• Administer isotonic IV fluids (lactated Ringer's or normal saline) at 20 mL/kg boluses when severe dehydration, shock, altered mental status, or failure of oral rehydration occurs. 1, 4
• Continue IV rehydration until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit replacement. 1

Nutritional Management

• Resume a normal, age-appropriate diet immediately during or after rehydration—do not withhold food or enforce fasting. 1, 3
• Avoid high-sugar beverages (soft drinks, undiluted fruit juice, sports drinks) and caffeinated drinks, as these worsen diarrhea through osmotic effects and increased motility. 3, 6

Pharmacological Adjuncts

• Loperamide may be used in immunocompetent adults with watery diarrhea once adequately hydrated: 4 mg initially, then 2 mg after each loose stool (maximum 16 mg/day). 4, 6
• Avoid loperamide in bloody diarrhea, high fever, or suspected inflammatory/invasive infection due to risk of toxic megacolon. 4
• Ondansetron (4-8 mg single dose) can facilitate oral rehydration when vomiting is prominent. 4
• Probiotics may modestly reduce symptom duration but are not routinely necessary. 3

Antibiotic Therapy (Rarely Indicated)

• Empiric antibiotics are not recommended for typical acute watery gastroenteritis because viral etiologies predominate. 1
• Consider antibiotics only for bloody diarrhea with high fever and systemic toxicity (suggesting Shigella, Salmonella, Campylobacter), persistent symptoms beyond 5-7 days, or immunocompromised hosts. 1, 4
• Avoid antibiotics if Shiga toxin-producing E. coli (STEC) is suspected due to increased risk of hemolytic uremic syndrome. 1

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic test results—begin ORS immediately based on clinical assessment. 3
• Do not use sports drinks or apple juice as primary rehydration fluids; they lack appropriate electrolyte balance and may worsen osmotic diarrhea. 3
• Do not withhold food during or after rehydration; early refeeding shortens illness duration and improves outcomes. 1, 3
• Do not prescribe antimotility agents for bloody diarrhea, high fever, or children under 18 years. 1, 4
• Do not order routine stool cultures in immunocompetent adults with typical watery diarrhea—reserve testing for red-flag presentations. 1, 5

Hospitalization Criteria

Admit patients with any of the following: 3, 4

• Severe dehydration (≥10% fluid deficit) or clinical shock
• Failure of oral rehydration therapy despite proper technique
• Altered mental status or severe lethargy
• Bloody diarrhea with fever and systemic toxicity (monitor for hemolytic uremic syndrome)
• Significant comorbidities or immunocompromised state
• Elderly patients (≥65 years) with lower threshold due to higher mortality risk