Evaluation of Acute Diarrhea in Adults
The evaluation of acute diarrhea in adults should be risk-stratified based on clinical severity, with most uncomplicated cases requiring only clinical assessment and supportive care, while reserving diagnostic testing for patients with bloody/mucoid stools, fever ≥38.5°C, signs of severe dehydration or sepsis, immunocompromise, recent hospitalization, or international travel 1.
Initial Clinical Assessment
Key History Elements to Obtain
- Onset and duration of symptoms (acute <14 days vs persistent ≥14 days)
- Stool characteristics: watery vs bloody/mucoid (inflammatory vs noninflammatory)
- Fever presence and temperature (≥38.5°C is significant)
- Travel history: recent international travel, particularly to developing countries
- Exposures: recent antibiotics, hospitalization, food handlers, outbreak settings
- Immune status: HIV, immunosuppressive medications, transplant recipients
- Frequency of bowel movements and associated symptoms (nausea, vomiting, abdominal pain) 2, 3
Physical Examination Priorities
Assess for:
- Dehydration severity: vital signs (pulse, blood pressure, mental status), skin turgor, mucous membranes, capillary refill
- Signs of sepsis: fever, tachycardia, hypotension, altered mental status
- Acute abdomen: peritoneal signs suggesting surgical pathology (ischemia, perforation) 2, 4
Diagnostic Testing Algorithm
When to Order Stool Studies
Diagnostic evaluation is indicated when:
- Bloody or mucoid diarrhea (dysentery)
- Fever ≥38.5°C
- Signs of sepsis or severe dehydration
- Immunocompromised state
- Recent hospitalization (consider C. difficile)
- Recent international travel
- Suspected outbreak
- Persistent symptoms >7 days
- Occupational risk (food handlers, healthcare workers) 1, 2
Most patients with uncomplicated acute watery diarrhea without these features do NOT require stool testing 1.
Recommended Diagnostic Tests
When testing is indicated:
- Molecular studies (PCR panels) are preferred over traditional stool cultures unless outbreak investigation is needed 2
- Complete blood count with differential
- Serum creatinine and electrolytes to assess dehydration severity
- Stool lactoferrin or fecal leukocytes for inflammatory diarrhea
- C. difficile testing if recent antibiotics or hospitalization
- Ova and parasites if persistent diarrhea or travel to endemic areas
- Blood cultures if sepsis suspected 1, 3
Severity Stratification
Risk Factors for Severe Disease
Patients at higher risk requiring closer monitoring:
- Age >65 years
- Immunocompromise
- Chronic kidney or liver disease
- Severe dehydration (altered mental status, hypotension)
- High fever (≥38.5°C)
- Bloody diarrhea
- Elevated white blood cell count
- Elevated serum creatinine 5, 6
Common Pitfall to Avoid
Do not routinely order stool studies in immunocompetent adults with mild, acute watery diarrhea and no alarm features—this leads to unnecessary testing, cost, and potential inappropriate antibiotic use 1, 2. The vast majority of these cases are viral and self-limited.
Management Priorities During Evaluation
While completing the evaluation:
Assess and correct dehydration immediately:
Avoid empiric antibiotics in most cases of acute watery diarrhea without travel history 1
Consider empiric antibiotics ONLY for:
- Bloody diarrhea with fever ≥38.5°C or signs of sepsis
- Recent international travel with moderate-severe symptoms
- Suspected enteric fever (after cultures obtained)
- Immunocompromised patients with severe illness 1
Avoid antibiotics in suspected STEC O157 or Shiga toxin-producing E. coli (increases hemolytic uremic syndrome risk) 1
The evaluation should be streamlined and cost-effective, reserving extensive workup for those with clear risk factors or severe presentations that impact morbidity and mortality.