What is the initial approach to managing a patient with fever and eosinophilia?

Initial Management of Fever and Eosinophilia

All patients presenting with fever and eosinophilia should undergo concentrated stool microscopy on three separate samples and receive empirical treatment with albendazole 400 mg twice daily for 3 days when investigations are negative, while simultaneously pursuing a detailed travel and exposure history to guide targeted therapy. 1, 2

Immediate Clinical Assessment

Critical History Elements

• Document exact countries visited, duration of stay, and timing of symptom onset relative to travel (incubation periods range from 1-2 weeks for Loeffler's syndrome to 2-9 weeks for Katayama syndrome). 1, 2

• Identify specific high-risk exposures:

  • Freshwater swimming in African lakes/rivers 2-9 weeks prior suggests acute schistosomiasis (Katayama syndrome). 1
  • Barefoot walking or soil contact indicates hookworm or strongyloides. 2
  • Raw meat consumption raises concern for toxocara. 1

• Review all medications started within the past 3 months, particularly NSAIDs, beta-lactam antibiotics, and nitrofurantoin, as drug reactions are common causes. 2

• Screen for organ involvement symptoms: dry cough, wheeze, urticarial rash, abdominal pain, diarrhea, or neurological symptoms, as these indicate specific syndromes requiring urgent treatment. 1

Initial Laboratory Workup

Essential First-Line Tests

• Calculate absolute eosinophil count (AEC) from CBC with differential to determine severity: mild (500-1500/μL), moderate (1500-5000/μL), or severe (>5000/μL). 2, 3

• Obtain concentrated stool microscopy on three samples collected on separate days, as this has high diagnostic yield for intestinal helminths. 1, 2

• Order comprehensive metabolic panel with liver function tests, LDH, and uric acid to assess for organ damage. 2

• Perform peripheral blood smear review to evaluate for dysplasia, monocytosis, or circulating blasts that would suggest myeloproliferative disease. 2

Syndrome-Specific Management

Katayama Syndrome (Acute Schistosomiasis)

If the patient has fever, eosinophilia >5000/μL, urticarial rash, and freshwater exposure in Africa 2-9 weeks prior, initiate empirical treatment immediately without waiting for confirmatory testing. 1, 2

• Treatment regimen: Praziquantel 40 mg/kg as a single dose, repeated at 6-8 weeks (eggs and immature schistosomules are relatively resistant to single-dose therapy). 1

• Add prednisone 20 mg daily for 5 days, as case series evidence demonstrates steroids reduce symptom duration. 1

• Note: Serology and stool/urine microscopy have low sensitivity during acute infection, so clinical diagnosis justifies empirical treatment. 1

Loeffler's Syndrome (Larval Migration)

For patients with fever, urticaria, wheeze, dry cough, and pulmonary infiltrates on chest X-ray occurring 1-2 weeks after potential exposure, diagnose clinically as symptoms occur during the prepatent period. 1

• Initiate empirical albendazole 400 mg twice daily for 3 days when investigations are negative, as this covers Ascaris, hookworm, and Strongyloides. 1

• Obtain chest radiograph to look for migratory pulmonary infiltrates that support the diagnosis. 1

Tropical Pulmonary Eosinophilia

Consider this rare hypersensitivity reaction to lymphatic filarial worms (W. bancrofti, B. malayi) in patients with fever, dry cough, wheeze, and breathlessness who are often initially misdiagnosed with asthma. 1

• This presentation is more common in visitors to endemic regions than long-term inhabitants. 1

Risk Stratification

When to Escalate Workup

Hypereosinophilia (AEC ≥1500/μL) is never explained by allergy alone and always requires further investigation to exclude secondary causes including parasites, drugs, and myeloproliferative disorders. 2, 3

• Measure serum tryptase and vitamin B12 levels if hypereosinophilia is present, as elevated levels are characteristic of PDGFRA/PDGFRB rearrangements that show exquisite responsiveness to imatinib. 2

• Values >20,000/μL are highly suggestive of myeloproliferative disorders and warrant urgent hematology consultation. 4

Watch-and-Wait Criteria

For mild eosinophilia (<1500/μL) without symptoms or signs of organ involvement, close follow-up with repeat testing may be acceptable after excluding parasitic causes. 2, 5, 6

Common Pitfalls to Avoid

• Do not rely on single stool sample: Sensitivity improves significantly with three samples on separate days. 1, 2

• Do not delay empirical treatment for Katayama syndrome: The clinical presentation (fever, rash, eosinophilia, freshwater exposure) justifies treatment before serologic confirmation. 1

• Do not assume allergy explains hypereosinophilia: AEC ≥1500/μL requires systematic evaluation for secondary and primary causes. 2, 3

• Do not miss medication-induced eosinophilia: Review all medications started within 3 months, as drug reactions are easily reversible causes. 2