What is the workup for viral gastritis?

Workup for Viral Gastroenteritis

In most clinical scenarios, viral gastroenteritis is a clinical diagnosis that requires no laboratory workup, as testing rarely changes management and the condition is self-limited. 1, 2

When Laboratory Testing Is NOT Indicated

For typical presentations in immunocompetent patients, no diagnostic workup is necessary. The diagnosis is clinical, based on:

• Acute onset of nausea and vomiting 3
• Watery, non-bloody diarrhea (may develop 24-48 hours after vomiting) 1
• Low-grade fever (high fever >39°C occurs in only one-third of cases) 1
• Duration of 12-60 hours for Norovirus or 3-8 days for rotavirus 1
• Absence of severe abdominal pain, peritoneal signs, or bloody diarrhea 1

Serum electrolytes, creatinine, and glucose measurements are unnecessary in most cases and should only be considered in children with severe dehydration requiring hospitalization and IV therapy. 4

When Diagnostic Testing IS Indicated

Individual Patient Testing

Testing should be pursued when:

• Bloody diarrhea is present - this is atypical for viral gastroenteritis and requires investigation for bacterial or other causes 2
• Immunocompromised patients with severe symptoms require endoscopic biopsy to diagnose CMV gastroenteritis, as peripheral blood or stool testing is insufficient 2
• Severe or localized abdominal pain that raises concern for surgical pathology (appendicitis, obstruction) requires CBC, basic metabolic panel, and urinalysis 1

Outbreak Investigation

Specimen collection is only indicated during outbreak investigations and must be done within the first 48 hours of illness onset. 3

Stool Specimens for Outbreak Investigation

• Collect within first 48 hours - viral shedding drops below detectable levels (1 million particles/ml) after 2-3 days 3, 5
• Bulk specimens from at least 10 ill persons - specimens must be loose enough to assume the shape of their containers; formed stools have low diagnostic yield 3
• Rectal swabs have no diagnostic value 2
• Store at +4°C, never freeze - freezing destroys viral morphology needed for electron microscopy diagnosis 3, 5

Paired Serum Specimens (Essential for Outbreak Diagnosis)

• Acute phase: Collect during first week of symptoms 3
• Convalescent phase: Collect during third to sixth week 3
• Quantity needed: 10 pairs from ill persons (same persons who submitted stool), 10 pairs from well persons 3
• Volume: Adults 10 ml, children 3 ml 3
• Collection: Use tubes without anticoagulant (red top tubes), spin off and freeze sera 3

Critical Pitfalls to Avoid

• Do not delay oral rehydration therapy waiting for laboratory results - begin rehydration immediately based on clinical assessment 2
• Do not collect specimens after 48 hours of illness - diagnostic yield becomes negligible as viral shedding decreases 3, 5
• Do not test vomitus, water, food, or environmental samples - viruses causing gastroenteritis cannot normally be detected in these specimens 3
• Do not assume viral etiology if bloody diarrhea is present - this requires investigation for bacterial causes 2

Red Flags Requiring Alternative Workup

Pursue alternative diagnoses with appropriate testing if:

• Prominent epigastric pain with focal tenderness - less typical for viral gastroenteritis which causes diffuse cramping 1
• Constipation rather than diarrhea - not typical of viral gastroenteritis and may indicate obstruction 1
• Fever >39°C or persisting beyond 48 hours 1
• Bilious vomiting - requires immediate imaging to rule out malrotation with volvulus 1
• Peritoneal signs (rebound, guarding, rigidity) - indicates surgical pathology requiring imaging 1