[Persistent Eosinophilia--differential diagnosis and work-up]

The differential diagnosis of eosinophilia is broad and constitutes a major challenge for both, the general practitioner and the hematologist. Whereas in developing countries secondary eosinophilia is commonly caused by parasitic infections, in Western and European countries eosinophilia is more often associated with atopic diseases or drug-related. This case-report presents an asymptomatic patient with marked persisting eosinophilia caused by Strongyloidiasis in whom parasitic stool examinations were repeatedly negative and infection could only be established by serologic testing.