Disseminated histoplasmosis in persons infected with human immunodeficiency virus.

Disseminated histoplasmosis is an AIDS-defining illness that occurs in about 5% of AIDS patients residing in histoplasmosis-endemic areas of the United States (the Mississippi and Ohio river valleys). This disease develops as a result of acute infection and perhaps also as the result of reactivation of latent infection: cases reported from areas such as New York City, where histoplasmosis is not endemic, are most likely due to reactivation of an infection acquired earlier in a histoplasmosis-endemic area, while cases in histoplasmosis-endemic areas are most likely due to acute infection, especially in outbreak settings. Disseminated histoplasmosis in HIV-infected patients is usually associated with advanced immunosuppression, with CD4+ lymphocyte counts of < 75/mm3. Currently, histoplasmin skin testing of HIV-infected patients does not seem to be useful in detecting previous exposure and therefore is not helpful in identifying groups of patients who are at risk for dissemination and who should be targeted for preventive efforts. The current public health recommendation for HIV-infected patients is to avoid exposure to sites likely to harbor high levels of Histoplasma capsulatum, such as chicken coops and bird roosts. The role of chemoprophylaxis is not clear, but an ongoing study by the Mycoses Study Group is evaluating the role of prophylactic itraconazole. If strategies for the prevention of disseminated histoplasmosis in HIV-infected patients are to be improved, studies must better define the risk factors for this opportunistic infection, describe its natural history, and develop more reliable tests to predict its development.