What is the most likely diagnosis and recommended management for a 68‑year‑old man who immigrated from the United States to the Philippines one month ago, presenting with a one‑month history of watery, crampy diarrhea (2–5 stools per day), vomiting, moderate fecal fat, negative stool ova‑and‑parasite exam, numerous leukocytes in urine, and normal electrolytes?

Diagnosis and Management

This patient most likely has chronic infectious diarrhea with steatorrhea (malabsorption), and the priority is to pursue additional stool testing for parasites—particularly Giardia and Cryptosporidium—along with repeat bacterial cultures, followed by empiric antibiotic therapy if testing remains negative, while also considering tropical sprue as a key differential diagnosis given the travel history and steatorrhea.

Most Likely Diagnosis

Giardiasis or other parasitic infection causing malabsorption is the leading diagnosis based on:

• One-month duration of watery diarrhea with steatorrhea (moderate fecal fat globules) in a recent immigrant from the US to the Philippines strongly suggests parasitic infection, particularly Giardia lamblia 1, 2
• The Philippines is endemic for parasitic infections, and approximately 10% of traveler's diarrhea is caused by parasitic infections that persist for weeks to months, with giardiasis being the most common 2
• Giardiasis is a classic infectious example of malabsorptive diarrhea characterized by excess gas, steatorrhea, or weight loss 3
• The negative initial ova and parasite exam does not exclude parasites, as the sensitivity of a single stool examination for parasites is low and repeated stool examinations are often needed 1

Key Alternative Diagnoses to Consider:

Tropical sprue must be strongly considered because:

• Tropical sprue presents with moderately severe malabsorption (steatorrhea), weight loss, and diarrhea in individuals from non-endemic areas who reside in tropical regions like Southeast Asia 4, 5
• Tropical sprue is associated with aerobic bacterial contamination of the small bowel and responds to antibiotics (tetracycline) and folic acid 6
• This diagnosis is often delayed because clinicians fail to consider it in the differential of diarrhea and weight loss in returning travelers 4

Celiac disease unmasked by infection is another consideration:

• Persistent travelers' diarrhea may unmask chronic gastrointestinal disorders such as celiac sprue, which presents with malabsorptive syndrome and steatorrhea 5
• However, this is less likely given the acute onset coinciding with immigration

Immediate Diagnostic Workup

Priority Testing:

1. Repeat stool examination with specific requests:

   • Test specifically for Giardia using antigen test or PCR, as these have sensitivity and specificity >95% 1
   • Specifically request testing for Cryptosporidium and Cyclospora, as microscopic examination of stool for ova and parasites is unlikely to include these organisms 2
   • Repeat bacterial stool culture for enteric pathogens 1
   • Consider immunofluorescence or enzyme immunoassay for specific parasites (Giardia lamblia, Cryptosporidium, Entamoeba histolytica) to increase sensitivity 1

2. Complete blood count to identify eosinophilia:

   • Returning travelers with diarrhea should have a complete blood count to identify eosinophilia, which suggests parasitic infection 1
   • Eosinophilia would support strongyloidiasis, though this typically presents differently

3. Serologic testing for strongyloidiasis:

   • For long-term travelers returning from countries highly endemic for strongyloidiasis (including the Philippines), serological blood test should be considered even in the absence of symptoms or eosinophilia 1
   • This is critical because Strongyloides stercoralis can produce overwhelming infection in immunocompromised persons and can persist indefinitely 1

4. Consider celiac disease testing:

   • Test for celiac disease with IgA tissue transglutaminase and a second test to detect celiac disease in the setting of IgA deficiency 1
   • This is important given the steatorrhea, though the acute onset makes this less likely

Additional Investigations if Initial Testing Negative:

• Microbiologic testing is recommended in returning travelers with persistent symptoms or those who fail empiric therapy 1
• Consider upper endoscopy with duodenal biopsies if parasitic testing remains negative, to evaluate for tropical sprue or celiac disease 5

Management Approach

Immediate Management:

1. Assess and correct hydration status:

   • Evaluate for dehydration (altered mental status, decreased urine output, orthostatic hypotension, dry mucous membranes) 7
   • The numerous urinary leukocytes may represent concentrated urine from dehydration rather than infection
   • Oral rehydration therapy is the mainstay 7

2. Empiric antibiotic therapy while awaiting test results:

   • Given one-month duration with vomiting requiring admission, empiric antibiotics should be used to treat severe travelers' diarrhea 1
   • Azithromycin is preferred to treat severe travelers' diarrhea 1
   • Azithromycin 500 mg daily for 3 days covers most bacterial pathogens and has some activity against parasites
   • Fluoroquinolones may be used but caution is advised due to emerging resistance, particularly in Southeast Asia 1

3. If Giardia is confirmed or highly suspected:

   • Metronidazole 250 mg three times daily for 5-7 days, or
   • Tinidazole 2 g single dose (preferred for compliance)

4. If tropical sprue is suspected (persistent symptoms despite negative parasitology):

   • Tetracycline and folic acid are effective treatments for tropical sprue 4, 6
   • Tetracycline 250 mg four times daily for 3-6 months plus folic acid 5 mg daily
   • Some patients respond to folic acid alone 4

Follow-up and Monitoring:

• If diarrhea persists ≥14 days despite treatment, pursue more extensive evaluation including upper endoscopy with duodenal biopsies 1, 7
• Monitor nutritional status and consider vitamin supplementation (B12, folate, fat-soluble vitamins) given malabsorption 3
• In patients with diarrhea lasting ≥30 days, testing for HIV may be appropriate 2

Critical Pitfalls to Avoid

1. Do not rely on a single negative ova and parasite exam – sensitivity is inadequate and specific testing for Giardia, Cryptosporidium, and Cyclospora must be requested 1, 2

2. Do not forget tropical sprue – this diagnosis is often missed in returning travelers and should be considered when parasitic testing is negative but malabsorption persists 4, 5

3. Do not assume all steatorrhea is parasitic – consider celiac disease, chronic pancreatitis, and bile acid malabsorption in the differential 1, 3

4. Do not overlook strongyloidiasis – serologic testing is essential as this can cause life-threatening hyperinfection if immunosuppression is later required 1

5. Do not delay empiric treatment – given the severity (vomiting requiring admission) and duration (one month), empiric azithromycin is justified while awaiting comprehensive testing 1