Diagnostics

• Clinical diagnosis

  • Perform a thorough history and physical examination.

  • Evaluate for risk factors for specific pathogens.

  • Evaluate for clinical features of dehydration and hypovolemia.

• Diagnostic studies are only recommended for the following:

  • Patients with severe gastroenteritis or risk factors for severe illness

  • And/or if the results may alter management

Suspect Shiga toxin-producing E. coli (STEC) gastroenteritis in patients with abdominal pain or tenderness and bloody diarrhea in the absence of fever.

Viral gastroenteritis may be asymptomatic or manifest with nonbloody watery diarrhea and vomiting, which is sometimes accompanied by abdominal pain or cramps, and fever.

• BMP and serum electrolytes: may show AKI or electrolyte abnormalities

• CBC

  • Leukocytosis with left shift: may indicate an inflammatory bacterial infection

  • Eosinophilia: may indicate a parasitic infection caused by invasive helminths

• Stool analysis (for inflammatory markers): may show leukocytes, occult blood, and/or lactoferrin

• Indications include:

  • Severe gastroenteritis or persistent diarrhea

  • Patients with risk factors for severe illness

  • Consider for patients with leukocytes and/or lactoferrin in the stool.

• Recommended studies

  • Obtain a stool culture to look for Shigella, Salmonella, Campylobacter, Yersinia, and STEC.

  • Alternatively, obtain non-culture-based studies.

• Further studies (in select cases)

  • Clostridioides difficile toxin: Obtain for patients with risk factors for C. difficile infection (CDI), e.g., recent history of antibiotic use.

  • Blood cultures

  • Stool microscopy (e.g., to identify ova and parasites)

  • Endoscopy (colonoscopy or sigmoidoscopy) : may show signs of inflammation (e.g., in infectious colitis)

Microbiological studies should be reserved for patients with fever, mucoid or bloody stools, signs of sepsis, immunosuppression, or severe abdominal cramping, and cases in which the identification of a causative pathogen would modify management.