A study of the complement fixation reaction in histoplasmosis.

Abstract A complement fixation test for histoplasmosis employing a whole yeast cell preparation as antigen was performed on sera from 2,000 individuals. Seven patients with culturally proved histoplasmosis were encountered. Sera from each of these patients reacted in the test, five at serum dilutions greater than 1:40, and the remaining two at 1:20 dilutions. Only two other reactions above 1:40 were found. These were in two sons of a proved case where there was strong epidemiologic evidence of active Histoplasma infection. Of the forty-nine persons suspected of having active Histoplasma infections on the basis of recent histoplasmin skin test conversion or pulmonary infiltrates along with positive histoplasmin and negative tuberculin skin tests, 50 per cent reacted in the complement fixation test. Conversely, among 300 persons in whom active Histoplasma infections seemed unlikely on the basis of negative histoplasmin skin tests, only one reaction occurred and that at the lowest (1:5) dilution employed. It was concluded that the complement fixation reaction has a definite usefulness in diagnostic studies for histoplasmosis. Some of the advantages and the limitations of the test are discussed.