Anthrax indirect microhemagglutination test.

A new application of the indirect microhemagglutination (IMH) test has been developed for anthrax. The antigen was prepared by DEAE cellulose, Dowex 1-X1, and Sephadex G-50 column chromatography of a culture filtrate of the avirulent, non-proteolytic, non-encapsulated Vollum strain of Bacillus anthracis grown anaerobically in a chemically defined liquid medium. Tanned, sensitized sheep red blood cells (SRBC) were tested with complement-inactivated SRBC-absorbed serum samples from 72 anthrax patients, 91 persons who had been vaccinated against anthrax, and 103 controls. The IMH test detected antibodies in 93% of patients, 98% of vaccinees, and none of the controls. Run-to-run reproducibility was 76% within one twofold dilution, and 93% within two twofold dilutions. The IMH test proved more sensitive and less time-consuming than the currently used agar-gel precipitation inhibition (AGPI) test.