Evaluation of a western blot test in an outbreak of acute pulmonary histoplasmosis

A western blot (WB) test was evaluated for detection of antibodies against native glycosylated and chemically deglycosylated M and H antigens of Histo plasma capsulatum in serum obtained from patients during the acute phase of pulmonary histoplasmosis that occurred during an outbreak. Of 275 serum sa mples tested by immunodiffusion and complement fixation (CF) samples from 4 0 patients affected during this outbreak: and from 37 negative controls wer e tested by WB test. A group of patients whose sera were negative for CF an tibodies and precipitins early in the acute stage of histoplasmosis but who all seroconverted during convalescence 6 weeks later were tested with the WB test. Antibodies against untreated H and M antigens were detected at a 1 :100 dilution by WE test in 45% of the 20 acute-phase serum samples and in all 20 of the convalescent-phase specimens. The WE test's sensitivity for a cute-phase specimens increased to 90% (18 of 20 specimens) when H and M ant igens were treated by periodate oxidation to inactivate susceptible carbohy drate epitopes, When native glycosylated antigens were used in the WE test, positive reactions were observed in negative control serum specimens (3 of 37 specimens; 8%) and in serum specimens obtained from asymptomatic person s screened as part of the outbreak investigation (13 of 20 specimens; 65%), These positive reactions were also attributed to glycosidic epitopes since the specificity of the WE test increased from 78 to 100% when periodate tr eated H and M antigens were used. WE test with deglycosylated H and M antig ens of histoplasmin provides a rapid, sensitive, and specific test to diagn ose acute pulmonary histoplasmosis before precipitins can be detected.