Provisional Diagnosis: Acute Infectious Gastroenteritis
The provisional diagnosis for an otherwise healthy adult presenting with acute diarrhea and fever is acute infectious gastroenteritis, most likely bacterial in etiology given the presence of fever. 1
Clinical Classification
This presentation falls into the category of acute watery or bloody diarrhea lasting <7 days, which the IDSA defines as acute gastroenteritis—a frequent cause of outpatient visits and hospitalizations in the United States. 1
Most Likely Pathogens Based on Fever
The presence of fever significantly narrows the differential diagnosis toward bacterial pathogens that warrant evaluation for potential antimicrobial therapy:
Primary Bacterial Suspects (in order of likelihood):
Salmonella enterica (35% of hospitalizations from bacterial gastroenteritis)—the leading cause of severe bacterial gastroenteritis requiring hospitalization 2
Campylobacter jejuni (28% of bacterial cases in younger adults)—the second most common bacterial pathogen, often presents with severe abdominal pain 2, 3
Shigella species (21% of bacterial infections)—particularly if the patient develops dysentery (frequent scant bloody stools with fever, abdominal cramps, and tenesmus) 2
Yersinia enterocolitica—especially if fever is prolonged (≥2 weeks) or there is a pseudo-appendicitis presentation 2
Viral Pathogens (Less Likely with Fever):
While norovirus is the most common overall cause of acute gastroenteritis in adults (58% of foodborne illness episodes), it typically causes low-grade fever in only 40% of cases during the first 24 hours and lasts 2-3 days. 1, 2 The presence of persistent fever makes bacterial etiology more probable. 1
Key Diagnostic Discriminators
Red-Flag Features to Assess:
High fever ≥38.5°C with systemic toxicity: Suggests possible enteric (typhoid/paratyphoid) fever requiring blood cultures 2, 1
Bloody diarrhea: Strongly indicates Shigella, Campylobacter, STEC, Salmonella, or Entamoeba histolytica 1, 2
Severe abdominal pain mimicking appendicitis: Consider Campylobacter or Yersinia 2
Duration of symptoms: Most bacterial gastroenteritis presents with mean diarrhea duration of 2.2 days at ED presentation 4
Frequency of stools: Bacterial infections typically produce 9-10 unformed stools per day 4
Important Clinical Pitfalls
Common misconception: Most patients with bacterial gastroenteritis do NOT present with high fever or bloody diarrhea. 4 In one ED study, mean temperature was only 37.5°C, and bloody diarrhea occurred in just 10.8% of culture-positive cases. 4
Dehydration assessment is critical: Fever increases fluid losses, and dehydration is the main complication requiring intervention, particularly in adults >65 years who have higher hospitalization and mortality rates. 1
Diagnostic Testing Indications
Stool testing IS indicated in this patient because fever is present, meeting IDSA criteria for evaluation. 1 Testing should include:
- Stool culture for Salmonella, Shigella, Campylobacter, and Yersinia 1
- Shiga toxin testing (to detect STEC) 1
- Clostridioides difficile testing if recent antibiotic use (within 8-12 weeks) 2
Blood cultures are indicated if: 1
- Temperature ≥38.5°C with signs of sepsis
- Enteric fever is suspected (especially with travel history to endemic areas)
- Patient appears systemically ill
Management Approach Pending Results
Empiric antimicrobial therapy is NOT routinely recommended while awaiting test results in immunocompetent adults with fever and diarrhea, UNLESS: 1
- Body temperature ≥38.5°C with signs of sepsis or recent international travel 1
- Clinical picture suggests bacillary dysentery (frequent scant bloody stools, high fever, severe cramps, tenesmus) presumptively due to Shigella 1
Supportive care priorities: 1
- Assess and correct dehydration with oral rehydration solutions (ORS) if dehydration is present
- Maintain adequate fluid intake guided by thirst
- Resume age-appropriate diet once rehydrated
Antimotility agents (loperamide) should be AVOIDED in the presence of fever, as they risk toxic megacolon and worsening outcomes. 1, 2