What is the diagnosis for a patient who developed nausea, vomiting, diarrhea, low-grade fever, and bone and joint pain 3 days after visiting a location?

Diagnosis: Traveler's Diarrhea with Possible Invasive Bacterial Infection

The most likely diagnosis is traveler's diarrhea caused by invasive bacterial pathogens (Shigella, Salmonella, or Campylobacter), and this patient requires immediate malaria exclusion, stool culture, blood cultures, and empiric antibiotic therapy with azithromycin. 1, 2

Critical First Step: Exclude Malaria

• Malaria testing must be performed immediately with three daily blood films, even though diarrhea is the presenting complaint. 1, 2
• Malaria represents 22.2% of all febrile illness in returning travelers and can present with gastrointestinal symptoms. 1, 2
• Never assume simple traveler's diarrhea when fever is present—this constellation demands broader evaluation for invasive pathogens and tropical diseases. 2

Diagnostic Workup

Immediate testing should include: 1, 2

• Three daily blood films for malaria (priority)
• Stool culture for Salmonella, Shigella, Campylobacter, and Yersinia
• Blood cultures (given fever with diarrhea suggesting possible enteric fever)
• Complete blood count with differential
• Assess hydration status carefully, as volume depletion is a frequently identified risk factor for diarrhea-related deaths 2

Most Likely Pathogens

The combination of fever with diarrhea 3 days post-travel strongly suggests invasive bacterial disease: 3, 2

• Campylobacter, Salmonella, or Shigella are the most common bacterial causes of traveler's diarrhea with fever. 3
• Enteric fever (typhoid) accounts for 2.3% of febrile returning travelers and typically presents with fever, headache, and abdominal pain (though diarrhea is actually uncommon). 2
• Norovirus or rotavirus are less likely given the presence of fever and bone/joint pain. 3

Key Distinguishing Features

This presentation has several red flags for invasive disease: 3, 2

• Fever with diarrhea indicates invasive bacterial infection rather than simple non-inflammatory traveler's diarrhea. 3
• Bone and joint pain (myalgia/arthralgia) can be part of the systemic inflammatory response to invasive bacterial infection. 3
• The 3-day incubation period is consistent with bacterial gastroenteritis (typical onset 4-14 days for most traveler's diarrhea, but can be as short as 6-72 hours for bacterial causes). 3

Empiric Treatment Recommendation

Start azithromycin 500 mg daily for 3 days (or 1-gram single dose) immediately after obtaining cultures: 3, 1, 2

• Azithromycin is preferred first-line for severe traveler's diarrhea with systemic symptoms (fever, significant illness). 1, 2
• Do NOT use fluoroquinolones empirically if travel was to Southeast Asia, where fluoroquinolone resistance in Campylobacter exceeds 85%. 3, 1
• For infants <3 months or if neurologic involvement develops, use a third-generation cephalosporin instead. 3
• Loperamide should be avoided in the presence of fever and should be discontinued immediately if fever or severe symptoms develop. 1

Alternative Diagnoses to Consider

If symptoms persist beyond 14 days or if specific features develop: 2, 4

• Amoebic dysentery (Entamoeba histolytica): Consider if bloody diarrhea develops with severe abdominal pain but minimal fever (fever occurs in only 8% of amoebic cases). 4
• Wet preparation of fresh stool (within 15-30 minutes) can identify motile trophozoites. 3, 4
• Treat with tinidazole or metronidazole if amoebic dysentery is confirmed. 3

Critical Pitfalls to Avoid

• Never delay malaria testing—even one episode of diarrhea with fever requires malaria exclusion, as malaria can be fatal if untreated. 1, 2
• Do not assume viral gastroenteritis when fever is present—this demands investigation for invasive bacterial disease. 3, 2
• Avoid empiric fluoroquinolones without knowing travel location, as resistance is widespread in Asia. 3, 1
• Monitor hydration status closely—volume depletion is a major risk factor for poor outcomes in traveler's diarrhea. 3, 2