Stool Concentrate Testing in Pediatric Parasitic Infection with Eosinophilia
All returning travelers and migrants with eosinophilia should be investigated with concentrated stool microscopy as a fundamental diagnostic test. 1
Essential Role of Concentrated Stool Testing
Concentrated stool microscopy is the cornerstone diagnostic test for identifying intestinal helminths that cause eosinophilia in pediatric patients. 1 The concentration process—using either sucrose flotation or formalin-ethyl acetate methods—significantly increases the sensitivity for detecting parasite ova and larvae that would otherwise be missed in direct examination. 1
Key technical considerations:
- Multiple samples are mandatory: At least 3 stool samples should be submitted because oocyst and egg excretion can be intermittent, meaning parasites may not be detected in every specimen. 1
- Timing matters critically: Eosinophilia may be transient during the tissue migration phase (prepatent period) when stool microscopy will be negative because eggs or larvae are not yet being shed. 1 Eosinophilia often resolves when organisms reach the gut lumen—paradoxically, this is when stool microscopy becomes positive. 1
Diagnostic Limitations and When to Add Serology
Critical pitfall: Concentrated stool microscopy has notably lower sensitivity for Strongyloides species compared to other soil-transmitted helminths. 1 This is particularly important because strongyloidiasis can progress to fatal hyperinfection syndrome in immunocompromised patients.
When stool microscopy is insufficient:
- Add strongyloides serology for all patients with eosinophilia, regardless of stool results. 1
- Add schistosomiasis serology (positive at 4-8 weeks post-exposure) when there is history of freshwater exposure in endemic areas, as stool microscopy has low sensitivity for schistosomiasis. 1
- Consider empirical treatment with albendazole 400 mg plus ivermectin 200 μg/kg for negative stool microscopy in children >24 months to cover prepatent or undetected geohelminth infections. 1
Specific Diagnostic Approach by Clinical Context
For acute presentations (Katayama syndrome, Loeffler's syndrome):
- Stool and urine microscopy may be negative during the acute phase when eosinophilia is highest. 1
- The combination of eosinophilia with fever and rash 2-8 weeks after freshwater swimming justifies empirical treatment even with negative microscopy. 1
For chronic diarrhea (>2 months) with negative stool exams:
- Endoscopy should be considered, as touch preparations can provide rapid diagnosis within 24 hours. 1
- This is particularly relevant for cryptosporidiosis and microsporidiosis in immunocompromised children. 1
Enhanced Diagnostic Techniques
Preferred methods beyond basic concentration:
- Monoclonal antibody-based fluorescein-conjugated stains and enzyme immunoassays are preferred over acid-fast staining for cryptosporidiosis due to enhanced sensitivity and specificity. 1
- Faecal PCR is more sensitive than concentrated stool microscopy for strongyloidiasis and other helminths, though availability is limited. 1
- Modified trichrome stain or Calcofluor white for microsporidia detection in thin smears. 1
Clinical Integration
In a pediatric patient with thrombocytosis and eosinophilia, concentrated stool microscopy serves as the initial high-yield test to identify common intestinal helminths (hookworm, Ascaris, Trichuris). 1 However, negative results do not exclude parasitic infection—particularly strongyloidiasis, schistosomiasis, or infections in the prepatent period. 1 The systematic evaluation must include both stool concentration and appropriate serological testing based on geographic exposure and timing of symptoms. 1, 2
Repeat testing is essential: If initial stool samples are negative but clinical suspicion remains high, repeat concentrated stool microscopy and consider alternative diagnostic methods or empirical treatment. 1, 3, 2