Diagnosis of cat scratch disease is usually confirmed when 3 of the following 4 findings are present: history of contact with an animal, usually a cat, and presence of a primary dermal or eye lesion; aspiration of a sterile pus from an involved lymph node or laboratory tests that exclude other causes of adenopathy; a positive delayed-hypersensitivity reaction in the skin to cat scratch antigen; and a node biopsy revealing characteristic histopathologic changes, especially if organisms can be identified with Warthin-Starry silver stain.