What should be tested in a patient presenting with gastrointestinal symptoms, including nausea, diarrhea, and vomiting, along with systemic symptoms like cold chills, tiredness, and weakness?

Diagnostic Testing for Acute Gastroenteritis with Systemic Symptoms

For a patient presenting with nausea, diarrhea, cold chills, tiredness, and weakness, obtain a detailed history focusing on fever presence, travel exposure, recent antibiotic use, and symptom duration—then proceed with targeted stool testing only if specific high-risk features are present. 1

Initial Clinical Assessment

Critical History Elements to Obtain Immediately

• Fever documentation: Measure temperature objectively, as fever with chills significantly increases likelihood of invasive bacterial pathogens 1
• Travel history within past 3 weeks: Any travel to endemic areas (especially sub-Saharan Africa, Southeast Asia, Latin America) mandates immediate malaria testing with thick and thin blood films 2
• Antibiotic exposure within past 3 months: This requires Clostridioides difficile testing regardless of other symptoms 1, 3
• Symptom duration: If <7 days with mild symptoms, microbial studies are unnecessary 4, 3
• COVID-19 exposure or associated symptoms: In high-prevalence settings, test for COVID-19 as GI symptoms may precede respiratory symptoms by several days 1
• Stool characteristics: Presence of blood, mucus, or frequency >3 watery stools per 24 hours 1

Physical Examination Priorities

• Vital signs for hemodynamic stability: Hypotension, tachycardia, or oxygen saturation <92% indicates need for immediate hospitalization and empiric antibiotics 1, 2
• Volume status assessment: Signs of dehydration (dry mucous membranes, decreased skin turgor, orthostatic changes) guide rehydration strategy 1
• Abdominal examination: Severe tenderness, guarding, or rigidity suggests complicated intra-abdominal infection requiring imaging 1

Laboratory Testing Algorithm

When to Test (High-Risk Features Present)

Order stool testing if ANY of the following apply:

• Fever ≥38°C (100.4°F) with diarrhea 1, 3
• Bloody or mucoid stools 1, 5
• Symptoms persisting >7 days 4, 3
• Recent antibiotic use (within 3 months) 1, 3
• Severe dehydration or inability to tolerate oral fluids 1, 4
• Immunocompromised state (chemotherapy, HIV, transplant, chronic steroids) 1
• Age >65 years or significant comorbidities 1
• Outbreak setting or food poisoning exposure 1

When NOT to Test

Avoid stool testing if:

• Mild symptoms with duration <7 days 4, 3
• No fever, no blood in stool, and patient tolerating oral fluids 4
• Immunocompetent patient with self-limited symptoms 3

Specific Tests to Order

For patients meeting testing criteria, obtain ONE stool sample for:

1. Multiplex PCR panel (preferred first-line test over traditional culture) including: 4, 3

   • Salmonella species
   • Shigella species
   • Campylobacter species
   • Norovirus
   • E. coli O157:H7 (if bloody diarrhea)

2. C. difficile toxin assay if antibiotic exposure within 3 months OR healthcare-associated diarrhea 1, 3

   • Submit single cup specimen of diarrheal stool
   • If first test negative but fever/abdominal pain persists, submit 1-2 additional specimens 1

3. Ova and parasite examination ONLY if: 1

   • Travel to endemic areas
   • Symptoms >7 days despite negative bacterial testing
   • Exposure to untreated water sources
   • Daycare exposure

Additional Laboratory Studies

Obtain blood work if fever present or severe illness:

• Complete blood count: Look for leukocytosis (bacterial infection) or thrombocytopenia <150,000/μL (suggests malaria if travel history present) 2
• Blood cultures (two sets from separate sites): Obtain BEFORE any antibiotics if fever ≥38°C, as bacteremia occurs in 5-15% of Salmonella cases 1, 2
• Basic metabolic panel: Assess for electrolyte abnormalities and renal function in dehydrated patients 1

For travelers with fever and chills:

• Malaria testing (thick and thin blood films): Mandatory for any febrile traveler from endemic area, as fever with chills has likelihood ratio of 5.1 for malaria 2

COVID-19 testing in appropriate settings:

• SARS-CoV-2 PCR or antigen test: Consider in high-prevalence areas, especially if associated symptoms include cough, shortness of breath, myalgias, headache, sore throat, or loss of taste/smell 1

Common Pitfalls to Avoid

• Do not order stool cultures as first-line test: Multiplex PCR has replaced traditional culture as the preferred diagnostic modality 4, 3
• Do not test for fecal leukocytes: Sensitivity is only 60-75% for C. difficile and lacks discriminatory value 1
• Do not perform stool testing for COVID-19: Inadequate evidence supports this practice despite viral shedding in stool 1
• Do not delay blood cultures waiting for stool results: Obtain blood cultures immediately if fever present, before any antibiotics 2
• Do not test after recent antibiotic use without considering false negatives: Antibiotic use correlates with negative PCR results even in true infections 6
• Do not order extensive testing in mild, self-limited illness: This increases costs without changing management 4, 3

Immediate Management Considerations

While awaiting test results:

• Start oral rehydration immediately for all patients tolerating oral intake 1, 4

• Initiate empiric antibiotics within 1 hour ONLY if: 1

  • Septic shock or hemodynamic instability
  • Severe immunocompromise
  • Suspected invasive bacterial infection with fever and bloody diarrhea
  • After obtaining stool and blood cultures

• Preferred empiric regimen for febrile bloody diarrhea: Fluoroquinolone (ciprofloxacin 500 mg PO twice daily) or azithromycin 500 mg daily if quinolone resistance suspected 1

Disposition decision:

• Hospitalize if: Oxygen saturation <92%, persistent hypotension, severe dehydration, altered mental status, age >65 with comorbidities, or immunocompromised 1, 2
• Discharge with close follow-up if: Stable vital signs, tolerating oral fluids, no high-risk features, and reliable for return precautions 7