When should Strongyloides (strongyloidiasis) infection be suspected and what diagnostic tests should be used in patients with a history of immunosuppression or recent travel to endemic areas presenting with gastrointestinal symptoms?

When to Suspect and Diagnose Strongyloidiasis

Clinical Suspicion Criteria

Suspect strongyloidiasis in any patient from endemic regions who will receive immunosuppressive therapy, particularly corticosteroids, regardless of symptom presence or eosinophilia status. 1

Geographic Risk Factors Requiring Screening

• Endemic regions include: Most of Africa, Central America, South and Southeast Asia, Middle East, former Soviet Union states, parts of South America, and rural Appalachian regions of the southern United States 1
• Long-term travelers (>1 month) to these areas warrant screening even years after exposure, as the parasite can persist indefinitely in the host through autoinfection 2
• IBD patients returning from endemic areas should be evaluated for strongyloidiasis even in the absence of symptoms or eosinophilia 2

High-Risk Immunosuppression States

• Corticosteroid therapy is the highest risk factor for precipitating fatal hyperinfection syndrome 1, 3
• Other immunosuppressive conditions: Anti-TNF therapy, calcineurin inhibitors, HTLV-1 infection, hematologic malignancies, and chemotherapy 1, 4
• Never initiate corticosteroids without Strongyloides assessment in at-risk patients—this can precipitate potentially fatal hyperinfection syndrome 1, 3

Clinical Presentations

Uncomplicated chronic infection: 1

• Asymptomatic carrier state (most common)
• Non-specific diarrhea and abdominal pain
• Larva currens (pathognomonic serpiginous urticarial rash)
• Löffler's syndrome (pulmonary infiltrates from larval migration)
• Peripheral eosinophilia (may be present but unreliable)

Hyperinfection syndrome: 1, 3

• Gastrointestinal symptoms: severe diarrhea, abdominal pain, gastrointestinal bleeding, malabsorption 5
• Pulmonary involvement: respiratory failure, diffuse infiltrates 4
• CNS involvement in disseminated disease
• Gram-negative bacteremia or sepsis without obvious source (due to larvae carrying enteric bacteria) 6, 5
• Eosinophilia is often absent during hyperinfection—do not rely on this for diagnosis 1, 4

Diagnostic Testing Algorithm

Primary Diagnostic Method: Serology

Serological tests (ELISA, immunoblot) are the primary diagnostic method due to superior sensitivity compared to stool examination. 7, 3

• Serological testing has sensitivity >80% for detecting strongyloidiasis 2
• Avoid ELISA tests with crude antigens due to low sensitivity and specificity 7
• Many experts recommend therapy for seropositive patients despite negative stool examinations 2

Stool Examination

• Single stool examination has low sensitivity for Strongyloides detection 2, 3
• Repeated stool examinations (at least 3 samples) are often needed to identify larvae 2
• Use concentration techniques (such as Baermann apparatus) as larval burden may be very low 8
• Microscopy sensitivity generally exceeds 80% for ova, cysts, and parasites overall, but is significantly lower for Strongyloides specifically 2

Additional Diagnostic Tests

• Complete blood count to identify eosinophilia (common in uncomplicated infection but may be absent in hyperinfection) 2, 7
• Endoscopic duodenal/jejunal biopsy can identify larvae when other methods fail, particularly in symptomatic patients 5
• Sputum or bronchoalveolar lavage may show larvae in pulmonary strongyloidiasis, though rare 7

Post-Treatment Monitoring

• At least three stool examinations over 3 months following treatment to ensure eradication, as recrudescence can occur up to 106 days post-treatment 8
• Use concentration techniques for follow-up stool examinations 8

Critical Clinical Pitfalls

• Never start corticosteroids without excluding or treating strongyloidiasis in at-risk patients—this is the most common precipitant of fatal hyperinfection 1, 3, 8
• Do not rely on eosinophilia for diagnosis or exclusion, as it may be absent during hyperinfection when diagnosis is most critical 1, 4
• Consider atypical presentations: unexplained Gram-negative bacteremia, aseptic meningitis, or recurrent enterobacterial sepsis in immunosuppressed patients from endemic areas 1, 5
• Empiric treatment should be considered for patients from endemic areas requiring urgent immunosuppression when timely testing is unavailable 1
• Strongyloidiasis in Europe may be more difficult to diagnose in travel-related infections than in immigrants 2