Peripheral blood eosinophilia as a clue to the diagnosis of an occult Coccidioides infection.

A marked peripheral blood eosinophilia is an uncommon finding in a complete blood count (CBC). According to Wardlaw and Kay (Eosinophils and Their Disorders. In: Beutler E, Lichtman MA, Coller BS, Kipps TJ, Seligsohn U, editors. Williams Hematology. 6(th) ed. New York: McGraw-Hill, 2001. p. 790-93), the most common causes are infection by helminthic parasites, atopic disease, and, less commonly, primary hypereosinophilic syndromes. Therefore, when eosinophilia is seen in a CBC, it can provide an important clue to the correct diagnosis. We present a case of a patient with a finding of pulmonary nodules in the setting of cancer and a CBC finding of profound peripheral blood eosinophilia. As a result of the high level of clinical suspicion for Coccidioides infection due in part to the eosinophilia, adequate steps were taken in the clinical laboratory not only to correctly diagnosis the patient, but also to protect the laboratory staff from work-related exposure to this easily aerosolizable infectious agent.