What is the most likely diagnosis of a 62-year-old male with 5 days of fever, diarrhea, and vomiting after traveling, with no apparent blood in vomit or stool?

Most Likely Diagnosis: Acute Viral Gastroenteritis (Norovirus)

The most likely diagnosis is acute viral gastroenteritis, most commonly caused by norovirus, given the 5-day duration of fever, vomiting, and nonbloody diarrhea in a patient with no sick contacts and domestic travel only. 1

Clinical Reasoning

Why Viral Gastroenteritis is Most Likely

• Norovirus is the primary diagnosis for acute viral gastroenteritis characterized by violent vomiting and nonbloody diarrhea lasting 2-3 days or less, though symptoms can extend to 5 days. 1
• Low-grade fever is present in approximately 40% of norovirus infections during the first 24 hours, which fits this patient's presentation. 1
• The absence of sick contacts does not exclude viral gastroenteritis, as transmission can occur through contaminated food or surfaces during travel. 2
• Viral gastroenteritis is the most common etiology of acute diarrhea in adults and is typically self-limited. 2

Why Bacterial Causes are Less Likely

• Bacterial gastroenteritis (Salmonella, Shigella, Campylobacter) is less likely due to the absence of bloody stools, which are characteristic of invasive bacterial disease. 1
• The majority of traveler's diarrhea is bacterial and lasts less than 7 days, but this patient traveled domestically (not internationally to a developing country), making bacterial causes less probable. 3
• Fever with diarrhea does suggest possible invasive bacterial disease, but the absence of blood in stool and the domestic travel history make this less concerning. 4

Why Parasitic Causes are Unlikely at This Stage

• Parasitic infections like Giardia typically cause persistent diarrhea lasting weeks to months, not 5 days. 3
• Evaluation for parasites should only be considered if diarrhea persists ≥14 days. 3, 1

Critical Exclusions Required

This Patient Does NOT Require Malaria Testing

• Malaria testing is only indicated for febrile illness after tropical travel to endemic areas. 4, 5
• Domestic car travel between locations (not specified as tropical/endemic) does not warrant malaria exclusion. 4

Recommended Management Approach

When Testing is NOT Indicated

• Stool testing should NOT be pursued in this case, as the patient has uncomplicated diarrhea without bloody stools, severe dehydration, or immunosuppression. 1
• Most cases of acute gastroenteritis do not require laboratory workup, and routine stool cultures are not recommended. 2

When Testing WOULD Be Indicated

• Pursue stool testing only if: 1
  • Diarrhea persists ≥14 days
  • Bloody stools appear
  • High fever (>38.5°C) persists beyond 24-48 hours
  • Severe dehydration develops
  • Patient is immunosuppressed

Appropriate Treatment

• Oral rehydration therapy with early refeeding is the mainstay of treatment. 1, 2
• Assess hydration status carefully, as volume depletion is a frequently identified risk factor for diarrhea-related deaths. 4, 5
• Antimotility agents like loperamide may be used for symptomatic relief in watery diarrhea, but should be avoided if bloody diarrhea develops. 2
• Probiotics may shorten the duration of illness. 2
• Antibiotics are NOT indicated for uncomplicated viral gastroenteritis. 1, 2

Common Pitfalls to Avoid

• Do not order stool cultures reflexively—this patient's presentation does not meet criteria for testing. 1
• Do not prescribe antibiotics empirically without evidence of invasive bacterial disease (bloody stools, severe systemic symptoms). 1
• Do not assume malaria risk from domestic travel—this only applies to tropical/endemic region travel. 4
• Signs of severe dehydration (altered mental status, decreased urine output, orthostatic hypotension) require immediate evaluation and aggressive rehydration. 1