Toxoplasma gondii and the compromised host. Antibody response in the absence of clinical manifestations of disease.

Toxoplasmosis is a well-described opportunistic infection in immunocompromised hosts. Meningoencephalitis, myocarditis, and pneumonitis are the most frequent clinical manifestations of disease. Because of difficulties both with isolation of the organism and with its identification in tissue, most laboratories rely on serological techniques for diagnosis of acute disease. The most widely available and commonly employed serological method is the indirect fluorescent antibody test (IFA). We recently encountered an immunocompromised patient with an undefined hematologic malignant neoplasm who had an IFA titer greater than 1:100,000 without clinical evidence of active toxoplasmosis. Although his dye test titer and direct agglutination titer were also elevated, he had negative double-sandwich-IgM enzyme-linked immunosorbent assay titers. Immunoperoxidase staining of the tissues failed to demonstrate trophozoites. This case demonstrates that elevated toxoplasma IFA titers may occur in patients at high risk for opportunistic infection but who do not manifest overt clinical toxoplasmosis.